Observational Study of Surface O3, NO , CH4 and Total ...A CH4 buildup was observed during early...

Aerosol and Air Quality Research, 14: 1074–1088, 2014 Copyright © Taiwan Association for Aerosol Research ISSN: 1680-8584 print / 2071-1409 online doi: 10.4209/aaqr.2012.11.0323

Observational Study of Surface O3, NOx, CH4 and Total NMHCs at Kannur, India T. Nishanth1*, K.M. Praseed2, M.K. Satheesh Kumar3, K.T. Valsaraj4

1 Department of Physics, Sree Krishna College Guruvayur, Kerala, 680102, India 2 Department of Physics, Sir Syed College, Taliparamba. Kannur, Kerala, India 3 Department of Physics, Govt. Brennen College, Thalassery, Kerala, India 4 Cain Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA 70803, USA ABSTRACT

This paper presents the results of measurements of the surface ozone (O3), oxides of nitrogen (NOx), methane (CH4) and

total non-methane hydrocarbons (TNMHCs) in a rural coastal location at Kannur (11.9°N, 75.4°E, 5 m asl), India from November 2009 to December 2011. The diurnal cycle for surface O3 had a peak in the afternoon and declined during nighttime. The maximum and minimum mixing ratio of surface O3 was observed in winter and monsoon seasons respectively. NOx concentration was high during mid-night to early morning and low during noontime. The diurnal variations of mixing ratios for NOx and O3 were anti-correlated. Monthly average maximum (2.26 ± 0.44 ppmv) and minimum (0.43 ± 0.19 ppmv) CH4 concentrations were observed in December and August respectively. The diurnal variations of CH4 were similar to that of NOx. A CH4 buildup was observed during early morning hours throughout the observational period. On an annual basis, the maximum, minimum and average total NMHCs were (25.45 ± 6.58 ppbv), (13.84 ± 4.31 ppbv), and (19.23 ± 5.56 ppbv) respectively at the observational site. Analysis of O3, NO, NO2, CH4 and NMHC have been carried out and the correlation between O3 and its precursors is discussed detailed. Further, the diurnal variation of O3 over a free tropospheric region at Ooty, a hill station lying in the Western Ghats region of south India on clear sky days in February 2011 is also reported for a comparison. Keywords: Air pollution; Surface ozone; Photochemical production; Hydrocarbons; Seasonal variations. INTRODUCTION

The concentrations of trace gases are low in the atmosphere, but they play a vital role in determining the ambient air quality over a location. Besides, trace gas chemistry can modulate radiative transfer by which it can affect the climate. In addition, the secondary species produced from pollutant trace gases impart environmental impacts. Ozone (O3) produced on the surface level is such a secondary species which serves as an ideal tracer to investigate the chemistry of trace gases. Moreover, (O3), produced on the ground is a secondary pollutant that influences human health and agricultural crop yield to a larger extent. O3 is produced in the troposphere when methane (CH4), non-methane hydrocarbons (NMHCs) and carbon monoxide (CO) are photo-chemically oxidized in the presence of nitrogen oxides (NOx). The diurnal cycle of O3 formation and destruction is driven by NOx and Volatile Organic Compounds (VOC) * Corresponding author.

Tel.: 91-09895415281 E-mail address: [email protected]

emissions (Peleg et al., 1997; Ryerson et al., 2001) and solar radiation. To retrieve O3 chemistry, it is necessary to estimate the concentration and reactivity of the different VOCs involved in O3 formation. Since surface O3 is produced by the dissociation of NO2 in the presence of sun light, the ratio of NO2/NO concentrations in the atmosphere is an indicator of O3 production. However, the abundance of VOC further modifies O3 chemistry more complex. Thus the O3 production efficiency depends on the concentration of VOC and NOx in a locality. Subsequently, the ratio of organic compounds like NMHC and NOx indicates the influence of VOC on O3 production at a site (Saito et al., 2002).

Now a day, satellite based observations are available for atmospheric trace gases monitoring all over the globe. However, ground based observations are highly significant to validate these space based measurements to study the chemistry, transport and modeling of these green house gases (Wang et al., 2009). Surface O3 in the atmosphere has been monitored at various sites around the globe for the past several decades (Oltmans, 1981; Volz and Kley, 1988). Many studies have been carried out on the photochemical characteristics of O3 and its precursor gases in the United States (Aneja et al., 1991; Qin et al., 2004; Alvarez et al., 2008; Yarwood et al., 2008), Europe (Zerefos et al., 2002;

Nishanth et al., Aerosol and Air Quality Research, 14: 1074–1088, 2014 1075

Mazzeo et al., 2005; Bossioli et al., 2007; Ordóñez et al., 2007; Solberg et al., 2008), and Asia (Pudasainee et al., 2006; Zhu et al., 2006; Bonasoni et al., 2008; Shan et al., 2008; Moore and Semple, 2009; Yin et al., 2010; Han et al., 2011). In the free troposphere region over Northern Hemisphere, increasing ozone concentration has been recently reported based on aircraft and ozonesonde data (Proberaj et al., 2009).

In the Indian sub-continent, various groups have carried out long-term measurements of surface O3 and precursors (Ghude et al., 2008; Kumar et al., 2010; Reddy et al., 2010; Singla et al., 2011; Mahapatra et al., 2012; Ojha et al., 2012; Sharma et al., 2013; Swamy et al., 2013) and the results were quite promising. Available observations and modeling studies in India show higher O3 levels during winter and summer seasons extending until May. Such variations are due to high precursor concentrations and the availability of ample solar radiation. Nair et al., (2002) found that sea breeze and land breeze have a pronounced influence on the production and transport of O3 at Thumba, a tropical coastal site in the south Indian city of Trivandrum. Measurements of surface O3, NOx and meteorological parameters at Kannur, another coastal city in south India by Nishanth et al. (2012b) reported that O3 and NOx showed distinct diurnal and seasonal variabilities. The observations conducted during 2009 to 2010 revealed that O3 production at Kannur is quite sensitive to the organic emissions. This study presents an account of the variability of surface O3 and its prominent precursor NOx in the wake of measured concentrations of methane and total non-methane hydrocarbons at this site. Location of the Study Area and General Meteorology

Kannur district in the State of Kerala, India lies between latitudes 11°40' to 12°48' North and longitudes74°52' to

76°07' east and covers an area of 2,996 km². Kannur can be geographically divided into highland, midland and lowland regions. Highlands are the mountainous region forming part of the Western Ghats and are covered by rainforests and plantations. The midland region comprises of undulating hills and valleys and the lowland is the narrow stretch containing rivers, deltas and the coastal region. The observations were carried out at the Kannur University Campus (KUC) (11.9°N, 75.4°E), situated 15 km north from Kannur town along the coastal belt of the Arabian Sea. This site is close to a National Highway (NH 17) and the Arabian Sea and is at a height of 5 m above mean sea level. Geographical location of observational site situated at Kannur University Campus, and the land use pattern of Kannur and its surroundings is shown in the Fig. 1.

In Kannur, the four major seasons are winter (December–February), summer (March–May), monsoon (June–August) and post-monsoon (September–November). The meteorological parameters such as wind speed, relative humidity, temperature and total rainfall experienced in the observational site were retrieved from the local automatic weather station operated by the Meteorological and Oceanographic Satellite Data Archival Centre (MOSDAC), established by the Indian Space Research Organization (ISRO). The total solar radiation was measured using a pyranometer installed at the local weather station of MOSDAC and the data were taken at 30 min time intervals. Fig. 2 shows the monthly average variations of meteorological parameters like wind speed, relative humidity, solar radiation, temperature and rainfall in Kannur. Generally, the wind speed is quite high during the period from June to September and low from December to April. The maximum and minimum humidity was observed during monsoon months and winter months respectively. Solar radiation is lower

Fig. 1. Geographical location of observational site situated at Kannur University Campus (black spot), and the land use pattern of Kannur and its surroundings.


J F M A M J J A S O N D

Win

d sp

eed (m

/sec

)

0

1

2

3

4

5

6

Tem

pera

ture

(OC

)

0

10

20

30

40

50

Relative hum

idity (%)

0

20

40

60

80

100

Wind speed

Temperature

Relative humidity

Month

Solar radiation (K

Wh/m

2/day)

0

2

4

6

8

10Solar radiation

J F M A M J J A S O N D

Rainfall (m

m)

0

100

200

300

400

500

600

700

800Rainfall

(a)

(b)

Fig. 2. Monthly average variations of (a) wind speed, relative humidity, solar radiation (b) temperature, rainfall during the period of study at KUC.

during monsoon season and is most intense during late winter and summer season. Influx of monsoon causes cloudy sky conditions over Kannur, leading to drastic reduction in solar radiation during June, July and August coinciding with the maximum rainfall. The temperature is high in the months March to May and is low during June through August. The highest rainfall was recorded during monsoon, while the lowest amount was observed in winter season. The most prominent meteorological feature at this location is the monsoon rainfall occurring in two spells in a year. The southwest monsoon is quite active during the months of June through August. About 80% of the total rainfall occurs from June to August, which constitutes the monsoon season. The region experiences easterly winds during winter months and westerly winds during summer months. During the first phase of the monsoon season (June–August), winds are stronger and the circulation is SSW (from ocean to land). The SSW wind gets weakened by September and northeasterly wind starts in November. The wind direction remains northeasterly until February, when the airflow is mostly from the continent. The months from December to February experience scanty rain and relatively low humidity which constitute the winter season at this site, while months from March to May is summer marked by high convective movement due to intense solar radiation. The period from

December to March records the maximum sunshine hours of more than 9.1 hours/day due to the clear sky and the minimum from June–August due to cloudy sky conditions.

Measurement Techniques

The concentrations of O3 and NOx were started to monitor from November 2009 and CH4 and total NMHCs were started to measure from October 2010 at Kannur University Campus (KUC) with the aid of ground-based gas analyzers obtained from Environment SA, France. Earlier, using this observational setup we studied the influence of solar eclipse on surface ozone (Nishanth et al., 2011) and air pollution due to fire cracking episode following festivals (Nishanth et al., 2012a) over this location and the results were quite promising. O3 present in the ambient air is measured by the analyzer (O342M), which is working on the principle of strong absorption of UV radiation at 253.7 nm by O3 molecules. The analyzer incorporates corrections due to changes in temperature, pressure in the absorption cell and drift in the intensity of the UV lamp. Calibration of the analyzer is performed using built-in O3 generator. The lowest detection limit of the analyzer is 0.4 ppbv with minimum response time of 30 s. The analyzer is provided with a built-in correction facility for temperature and pressure variations as well as the intensity fluctuation of the UV lamp.


The NOx analyzer (AC32M) is working on the principle of chemiluminescence effect produced by the oxidation of NO by O3 molecules, which peaks at 630 nm radiation. In the present study NO2 is measured by converting it into NO using the thermal conversion method using a heated molybdenum converter. The molybdenum converter is found to have higher sensitivity and 100% conversion efficiency (Winer et al., 1974; Finlayson-Pitts and Pitts, 1986). It has been realized that molybdenum converter also converts other species such as Peroxy Acetyl Nitrate (PAN), Nitric acid (HNO3) etc; however PAN is thermally unstable at temperature above 30–35°C and its concentration is may be very small at the surface level (Naja and Lal, 2002; Nishanth et al., 2012b). Since NOx analyzer does not have a blue light converter to distinguish between NO2 present in the ambient air and NO2 produced in the molybdenum converter by the oxidation of PAN, HNO3 etc.; NOx represents the total NOx measured at this site. The analyzers have been calibrated by using sample gases on a regular basis. Calibration procedure is based on the photometric assay of O3 concentration in a dynamic flow system. The concentration of O3 in the absorption cell of the analyzer is determined from the estimation of the intensity of 253.7 nm radiation absorbed by the sample. In practice, a stable O3 generator is used to produce O3 concentrations over the required range. Calibration of NOx analyzers is performed by using permeation tube oven. In this gas analyzer, the flow volume is controlled at the specified level so that the pressure in the reaction chamber is maintained at a constant value. Generally, a standard gas of NO2 is commonly used to check the performance of the converter efficiency as described by Rehme (1976).

CH4 and total NMHCs were measured using HC51M analyzer from Environment SA, France. Flame Ionization Detection is used as a versatile tool for monitoring hydrocarbons present in the ambient air. Hydrocarbon analyzer works on the principle of Flame Ionization Detection (FID) scheme by igniting hydrogen gas with ambient air to reveal the signature of organic species. Its great sensitivity, wide scope of linearity makes it an ideal detector for the measurement of hydrocarbons. Facilities like auto calibration, auto zeroing, automatic adjustment of change in meteorological parameter and data acquisition are built-in in the instrument. The analyzer has been calibrated by using sample gases on a regular basis. Further, for measuring the concentrations of C2-C5 hydrocarbons present in the ambient air, samples were collected in evacuated borosil glass flasks of 0.5 L capacity which are fitted with needle valves both its ends. The air samples were collected at a height of 2 m above the ground level from different locations in Kannur by using a battery operated pump for a period of 15 minutes.

RESULTS AND DISCUSSION Diurnal Variation and Rate of Change of O3 during Different Seasons

During the day, surface O3 concentration starts to increase gradually after sun rise, attains maximum value throughout noontime and then decreases to low value

during night and early morning hours. The daytime increase in O3 concentration is due to active photochemistry in the presence of intense sun light. Variation in O3 concentration is also influenced by boundary layer processes, regional emission, long range transport and meteorology. Generally, the boundary layer height increases after sunrise, reaching a maximum during noontime and descends after sunset (Mahalakshmi et al., 2011). During the day, O3 are characterized by high concentration (16–49 ppbv) in the noontime and low mixing ratio (3–15 ppbv) in the late evening and early morning hours. The minimum O3 mixing ratio of about (4.1 ± 1.2 ppbv) is noticed during the early morning around 06:00–07:00 h in all months of the year. Table 1 depicts the annual surface O3 variation, monthly average daytime, nighttime O3 mixing ratios and the observed maximum-minimum values at KUC from November 2009 to December 2011. From this table, it is evident that the highest (49.83 ppbv) O3 mixing ratio was observed in December while lowest (16.41 ppbv) mixing ratio was observed in July. The daytime (08:00–20:00 h) average high O3 mixing ratio observed in December (33.71 ± 5.29 ppbv) may due to the shallow boundary layer, low relative humidity and clear sky days that usually occurred in winter. Devara and Raj (1993), Praveena and Kunhikrishnan (2004) have observed that the Atmospheric Boundary Layer (ABL) height is low during monsoon and winter period over the Indian subcontinent. In monsoon, the strong prevailing winds disperse the pollutants quickly and get them washed out by precipitation. In contrast to this, both winds and ABL depth are low over Indian subcontinent by which the pollutants get trapped during winter (Alappattu et al., 2009). The daytime average low O3 mixing ratio (10.81 ± 3.84 ppbv) observed in July was mainly due to the intense south-west monsoon which washes out pollution over this location.

Fig. 3(a) shows the diurnal variations of mean O3 with 1σ standard deviation during different seasons and this reveals that O3 is high in winter and low during monsoon seasons. During winter, maximum (44.20 ± 5.70 ppbv) and minimum (4.75 ± 1.75 ppbv) concentrations of O3 were observed at 15:00 h and at 07:00 h respectively. During summer, maximum (33.77 ± 6.29 ppbv) mixing ratio of O3 was observed at 15:30 h and minimum (4.73 ± 1.78 ppbv) was at 06:30 h. During monsoon season, the highest O3 mixing ratio (18.49 ± 4.98 ppbv) was observed at 14:00 h and the lowest observed (2.74 ± 1.56 ppbv) at 07:30 h. In monsoon season, peroxy radicals (HO2 and RO2) are washed away by wet deposition limiting the gas phase photochemistry of O3 (Seinfeld and Pandis, 2006). During post monsoon season, the maximum O3 mixing ratio (29.32 ± 5.54 ppbv) was observed at 15:00 h and minimum of (3.71 ± 1.67 ppbv) at 07:00 h. During winter, the northeasterly wind brings dirty continental air from the northeast parts of Kannur and this could lead to the buildup of O3 precursors over this location during winter. On the other hand, at all seasons except in winter months, air mass comes over the Arabian Sea brings clean marine air over this coastal site. The seasonal pattern showed O3 concentrations starts decreasing from December to June; this could be due to (i) active rainfall occurs from June (SW monsoon) at this site and (ii) change in the wind


Table 1. Monthly daytime and night average, observed maximum and minimum O3, and the total days of observations

from 2009 November to 2011 December.

Month Average O3 (ppbv) Observed O3 (ppbv)

Total observational daysDay time

(08:00–20:00 h) Night time

(20:00–08:00 h) maximum minimum

January 30.06 ± 4.92 6.01 ± 1.59 45.65 4.56 46 February 26.44 ± 4.94 5.94 ± 1.64 40.99 4.13 45

March 22.49 ± 4.95 5.98 ± 1.69 36.93 4.18 51 April 20.44 ± 5.08 5.8 ± 1.74 32.99 4.75 47 May 21.38 ± 4.72 6.05 ± 1.69 31.46 4.83 49 June 13.13 ± 3.84 4.46 ± 1.55 44.07 3.11 36 July 10.81 ± 3.84 3.61 ± 1.38 16.41 2.34 33

August 11.18 ± 3.76 4.36 ± 1.46 18.53 2.57 41 September 14.05 ± 3.96 4.62 ± 1.58 23.37 2.83 43

October 16.06 ± 3.83 5.72 ± 1.46 28.24 3.79 47 November 25.71 ± 4.69 6.54 ± 1.97 39.12 3.89 71 December 33.71 ± 5.29 6.63 ± 1.69 49.83 5.33 74

Time (IST)

2 4 6 8 10 12 14 16 18 20 22 24

Ozo

ne (

ppbv

)

0

10

20

30

40

50

60

(b)

0 2 4 6 8 10 12 14 16 18 20 22 24

[dO

3]/d

t (pp

bv/h

r)

-15

-10

-5

0

5

10

15

(a)

Winter Summer

Monsson Post monsson

Winter Summer

Monsoon Post monsoon

Fig. 3. Diurnal variation of (a) surface O3 in different season (b) rate of change of O3 in different season from November 2009 to December 2011.

direction from northeasterly to southwesterly. The rate of change of O3 with respect to time, [d(O3)/dt]

for various seasons is shown in Fig. 3(b). It is clear that the rate of change observed was high during winter and its magnitude was of the order of 9.5 ppbv/hr at 10:00 h and 10.5 ppbv/hr at 11:00 h. The lower boundary layer heights during winter time may trigger higher pollutant concentrations in the presence of cloud free sky conditions and low

relative humidity may enhance a maximum change in the O3 concentration (Reddy et al., 2012). The rate of decrease of O3 was high during evening and was 11.6 ppbv/hr and 12.3 ppbv/hr at 18:00 h and 19:00 h respectively in winter months. The maximum [d(O3)/dt] in summer was 7.1 ppbv/hr at 11.00 h. The [d(O3)/dt] was almost zero at 14:00 h both winter and summer season and increased to 1.8 ppbv/hr for winter and 1.6 ppbv/hr for summer after which it became negative. The lapse rate [d(O3)/dt] showed sharp changes during 18:00 to 19:00 h which can be attributed to the faster O3 titration during this time. During midnight [d(O3)/dt] was found to be almost steady. During midnight, O3 chemistry becomes less intensive and surface deposition likely becomes the main process for O3 loss. A large fraction of O3 loss by surface deposition occurs through direct uptake by vegetation through the stomatal pores (Wesely, 1989; Wesely and Hicks, 2000). Environmental factors such as temperature, humidity and solar flux are known to have important impacts in regulating stomatal uptake; however, they also play a role in non-stomatal uptake as well. Surface wetness also appears to play a crucial role in O3 deposition (Altimir et al., 2006); however, this effect can be variable depending on the ecosystem. During monsoon and post monsoon seasons [d (O3)/dt] showed very little change of 5.2 ppbv/hr and 5.5 ppbv/hr at 11:00 and 12:00 h respectively, which was the lowest of all the seasons. There was also a negative rate of change during late evening and it was found to be steady over night hours. This is due to the absence of photochemical processes and the possibility of washout effect.

Rate of change of O3 during morning and evening at KUC and other observational sites in India are shown in Table 2 for comparison. The value of average rate of production of O3 during morning as well as in evening hours was observed high at KUC than other rural, semi arid-rural, coastal and sub urban locations in India. Rate of change of O3

during morning (08:00–11:00 h) was 4.9, 4.5, 4.6, 3.1

ppbv/hr at KUC, Joharapur, Gadanki and Tranquebar which are considered to be rural sites in south India. The annual average rates of change of O3 during the evening hours (17:00 to 19:00 h) at KUC was estimated to be –6.4 ppbv/hr


Table 2. Rate of change of O3 concentration at KUC and other sites in India.

Observation site Type of location Rate of change of O3 (ppbv/hr)

References 08:00–11:00 h 17:00–19:00 h

Kannur Rural coastal 4.9 –6.4 Present study Mohal Semi-urban 7.3 –5.9 Sharma et al., 2013

Pantnagar Semi-urban 5.6 –8.5 Ojha et al., 2012 Dayalbag Suburban site 2.2 –2.3 Singla et al., 2011 Anantapur Semi-arid rural 4.6 –2.5 Reddy et al., 2010 Joharapur Tropical rural 4.5 –3.3 Debaje et al., 2006 Thumba Tropical coastal 5.5 –1.4 Debaje et al., 2006

Tranquebar Rural coastal 3.1 –2.8 Debaje et al., 2003 Ahmedabad Urban 5.9 –6.4 Naja and Lal, 2002

Pune Urban 4.8 2.6 Naja and Lal, 2002 Delhi Urban 4.5 –5.3 Naja and Lal, 2002

Gadanki Rural 4.6 –2.6 Naja and Lal, 2002

which is higher than other rural sites Joharapur (–3.3 ppbv/hr), Gadanki (–2.6 ppbv/hr) and Tranquebar (–2.8 ppbv/hr), which indicating KUC is more polluted than these two sites. Thumba, a tropical coastal site in south India showed a higher production rate in the morning than KUC. The average rates of production of O3 during morning hours and lapse rate during evening hours are quite higher in the Indo Gangetic region (Pantnagar and Mohal). This suggests that the NOx emissions could be higher over Indo Gangetic region compared with other observational sites in India (Ojha et al., 2012). The rates of change of O3 during the evening hours at urban sites Delhi and Ahmadabad were higher than the morning hours, which are attributed to the higher NOx concentration from commuter vehicular emissions, responsible for fast titration of O3 in the evening. Usually, NO levels are observed to be lower at rural sites than at urban sites, which lead to slower ozone titration by NO during evening hours at a rural site (Naja and Lal, 2002).

Diurnal Variations of Oxides of Nitrogen

NO is a primary air pollutant whereas NO2 is a secondary pollutant produced through a set of complex reactions, which determines ambient O3 concentrations (Jenkin and Clemitshaw, 2000; Seinfeld and Pandis, 2006). Monthly average NO, NO2, and NOx concentrations measured from 2009 to 2011 with one sigma standard deviation are shown in Fig. 4(a). NO concentration was found to be low in day time, high at night and early morning hours during most of the observational period. The maximum and minimum concentrations of NO observed at KUC were (2.65 ± 0.46 ppbv) and (0.85 ± 0.24 ppbv) in the month of February. Similar to NO, diurnal variations of NO2 showed minimum concentrations during noontime and it peaked during late night and early morning hours. Maximum (2.75 ± 0.48 ppbv) and minimum (0.72 ± 0.21 ppbv) concentrations of NO2 were observed in December and August respectively. During nighttime and daytime, the variations in NO were quite similar to that of NO2.

Diurnal variation of NOx for different seasons at KUC is shown in Fig. 4(b). NOx

mixing ratios were generally higher during early morning and night time throughout all seasons. During the entire period of observations, NOx concentration

Month

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Ave

rage

conc

ent

ratio

n (pp

bv)

0

1

2

3

4

5

(b)

Time (IST)

2 4 6 8 10 12 14 16 18 20 22 240

1

2

3

4

5

6

(a)

Ave

rage

NO

x (p

pbv)

NO NO2 NOx

Winter SummerMonsoon Post monsoon

Fig. 4. (a) Monthly average variations of NO, NO2, NOx (b) Diurnal variation of NOx for different seasons at KUC from November 2009 to December 2011.

was high during late night hours and early morning and low during noontime. Seasonal average maximum NOx concentration was observed in winter and minimum in monsoon. Average NOx concentration in winter, summer, monsoon and in post monsoon were (3.36 ± 0.50 ppbv), (3.16 ± 0.4 ppbv), (2.9 ± 0.36 ppbv), (3.02 ± 0.44 ppbv) respectively. The concentration of NOx did not show significant variation during the period of observation at this site but only had a small seasonal variation. During the period of observation, the maximum (4.65 ± 0.76 ppbv) and


minimum (1.83 ± 0.28 ppbv) concentrations of NOx mixing ratios were observed in January and February respectively.

Near to the observational site, traffic starts to buildup during morning hours, which causes a peak pollutant level around 06:00 to 09:00 h. During these hours, NOx concentrations started to increase due to hydrocarbons from vehicles and their reactions to produce ozone. Variations in NOx are caused by variations in boundary layer mixing processes, chemistry, anthropogenic emissions and local surface wind patterns (Rao et al., 2002; Mazzeo et al., 2005; Shan et al., 2009). During noontime, the higher boundary layer provided a larger mixing region and hence diluted the pollutants. On the other hand, during evening hours, pollutant emissions from vehicles get trapped in the descending boundary layer. Moreover the boundary layer remains low during winter season (Beig et al., 2007). The maximum rate of change of O3 occurred in December, where observed NOx concentration was high and the minimum rate of change of O3 was in July, during which NOx concentration was the lowest. During winter season, the convective activities and turbulent mixing were weak which lead to a lower boundary layer height (Ramana et al., 2004). As a result, the concentration of pollutants near the surface increases. In addition to this, biomass burning on the eastern side of the observation site was quite intense during winter season causing transport of NO, NO2, CO, NMHC over to this location.

Relationship between Surface O3 and Oxides of Nitrogen

During the entire period of observations, we found that the diurnal variations of NOx mixing ratios showed opposite cycles to that of O3 and thus these two are anti-correlated. Several studies have revealed that morning production and evening-nighttime lapse rates of O3 are proportional to the NOx concentration (David and Nair, 2011; Song et al., 2011). Photochemical production of O3 takes place during daytime initiated by oxidation of its precursors. As has been discussed, the NOx plays a critical role in the photochemical formation of O3 and has been found to be a limiting factor in the atmosphere at rural and remote locations (Finlayson-Pitts and Pitts, 2000). O3 production during day time is driven by the photochemical reaction between hydroxyl radicals (OH), organic peroxy radicals and NO, while it is removed at night by dry deposition and destruction by alkenes and NO. The conversion of NO to NO2 by O3 during the night is the primary reaction that increases NO2 at night, with the reverse occurring during the day to increase O3 and decrease NO2 (Mazzeo et al., 2005). In addition, the relatively low air temperature near the ground at night could prevent the vertical dispersion of NOx, contributing to its accumulation and resulting in higher night-time concentrations. Surface O3 is formed and destroyed in a series of reactions involving NO and NO2. The O3 and NOx concentrations show inverse relationship due to titration of O3 during the daytime. This is similar to what is observed in most other parts of the world (Chameides and walker, 1973; Stephens et al., 2008; Song et al., 2011; Sun et al., 2011).

Fig. 5(a) represents the variation of O3 concentration with

NO mixing ratio within a sample interval of 15 minutes. It is evident that O3 concentration diminishes as NO mixing ratio increases, which may be due to the removal of O3 by titration with NO. The most appropriate fit between O3 and NO levels observed in two years time is exponential and similar to our earlier observation (Nishanth et al., 2012c) and the empirical relation is [O3] = 75.96 exp (–1.50[NO]) (1)

A fast decay in O3 concentration was observed at high NO mixing ratios from late evening to early morning. The daytime variation between O3 and NO2 observed on clear sky days available during winter mornings is shown in Fig 5(b). A linear fit with excellent correlation with a significance level (p < 0.01) that occurs on clear sky days in winter season reveals the active photochemistry of O3 production, which starts early morning.

The empirical relationship observed between [O3] and [NO2] is [O3] = 2.72[NO2] + 4.32 (2)

O3 and NOx shows a very strong inverse correlation during the period of observations suggesting the possible

(a)

NO (ppbv)

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50

Ozo

ne

(ppb

v)

0

10

20

30

40

50

60

(b)

NO2 (ppbv)0.8 1.0 1.2 1.4 1.6 1.8 2.0

Ozo

ne

(ppb

v)

6.5

7.0

7.5

8.0

8.5

9.0

9.5

10.0

Correlation coefficient (r) = -0.81[O3]=75.96 exp {-1.50[NO]}

Correlation coefficient (r) = 0.89[O3]=2.72 [NO2] + 4.32

Fig. 5. Scatter plot showing the variation of O3 concentration with NO (b) correlation between O3 and NO2 in winter morning.


VOC sensitive characteristics of the study location as described by Seinfeld and Pandis (2006) and Song et al., (2011).

To reveal the photochemical production of O3 from NO2, a correlation between variations of [NO2]/[NO] and O3 is made and is presented in Fig. 6. A higher cluster of low O3 values were found at lower values of [NO2]/[NO] and only few data points representing higher O3 values were found at higher values of [NO2]/[NO]. A logarithmic fit represents this behavior and an empirical relationship was obtained and this can be used to project the O3 concentration at this site during daytime as [O3] = 11.89 ln([NO2]/[NO]) + 18.30 (3)

Based on the two year data, a good correlation of 0.77

between O3 and [NO2]/[NO] is found and the correlation coefficient has a significance level of p = 0.01. O3 has a tendency to stabilize beyond 44 ppbv mixing ratio and this shows that at higher levels of [NO2]/[NO], O3 concentration is close to reaching a photostationary state (Shao et al., 2009). Interestingly, at KUC, where there are small local emissions of NOx, its ambient concentrations are generally much lower than other suburban sites in India. Similar analyses were carried out with one year data from 2009 to 2010 between O3 and NOx for KUC (Nishanth et al., 2012b) and it was found that the correlation pattern remained unchanged even after projecting their variations with two year data which confirmed the variations of O3 and NOx at this site. Diurnal Variation of CH4 at KUC

One year observation of O3 and NOx realized that organic compounds present in the ambient air over Kannur have a significant impact on the production of ground level O3 at Kannur (Nishanth et al., 2012b). Realizing the crucial roles in photochemical production of O3 and their large local emission sources, measurements of CH4 and total NMHCs at KUC have been carried out since October 2010. Monthly 0.19) ppmv CH4 concentrations were observed in December average maximum (2.26 ± 0.44) ppmv and minimum (0.43 ± and in August. The diurnal variations of CH4 were similar

[NO2]/]NO]

0 1 2 3 4 5 6 7 8

Ozo

ne (

ppbv

)

0

10

20

30

40

50

60Correlation coefficient (r) = 0.77[O3]= 11.89 ln [NO2]/[NO]+ 18.30

Fig. 6. Day time variation of O3 with [NO2]/[NO].

to that of NOx and we found that CH4 showed a buildup during early morning hours from the nearby wet lands, paddy fields and river basin. CH4 was observed to be very low during noon time and thereafter started to increase during evening hours for all months. During evening hours, increase in the emission of hydrocarbons from the vehicles and trapping in the boundary layer caused an increase in NMHC. CH4 concentrations were low during the southwest monsoon seasons (June–August) during which the observational site experienced the highest rainfall of the year. Thus, there was also the possibility of wet deposition removal of organic pollutants. This scenario continued in post monsoon season as well.

Diurnal variation of CH4 for seasonal average basis at KUC is shown in Fig. 7(a). On a seasonal basis, maximum CH4 concentration was observed in winter and minimum in monsoon. The rate of change of CH4 was found to be high during winter and minimum during the monsoon season and late evening and night hours for all seasons. After attaining a higher value in the morning, there was a decrease in the rate of change in noon time in all seasons. There are many anthropogenic sources which account for high CH4 levels observed in winter and summer seasons at KUC such as swampy habitats, shallow ditches and puddles including low lying rice cultivation areas along the bank of Valapattanam River, near the observational site. Both biological and physical processes control the exchange of CH4 between rice paddy fields and the atmosphere. This may be one of the major reasons for the enhanced CH4 observed during winter seasons.

Non-methane hydrocarbons (NMHCs) play an important role in the chemistry of the troposphere as precursors of O3 and PAN. In polluted environments, the photo-oxidation of NMHCs in the presence of NOx lead to the formation of O3. The importance of NMHCs as O3 precursor depends largely on their reactivities and ambient concentrations. Measurements of biogenically emitted VOCs such as isoprene suggest that these compounds contribute to high O3 concentrations in urban areas. Major urban sources of NMHCs are releases from chemical industries, refinery operations, solvent evaporation and vehicular exhaust (Pandit et al., 1990; Liu et al., 2008). Seasonal variations in NMHCs concentrations are mainly influenced by the photochemical removal, source strengths, dilution due to atmospheric mixing of air parcels and transport from source regions to the sampling site (Klonecki et al., 2003).

Diurnal variation of CH4 and total NMHCs as annual hourly average are shown in Fig. 7(b). Clear seasonal variabilities were identified for CH4 and total NMHCS with distinct maxima during winter season and minima in monsoon season. On an annual basis, maximum, minimum and average CH4 were (1.35 ± 0.39 ppmv), (0.83 ± 0.23 ppmv), (1.12 ± 0.29 ppmv) and total NMHCs were (25.45 ± 6.58 ppbv), (13.84 ± 4.31 ppbv), (19.23 ± 5.56 ppbv) respectively. Backward air mass trajectory analysis using HYSPLIT model (Nishanth et al., 2012b) and CGER-METEX reanalysis data (Nishanth et al., 2012c) during the period of observation revealed that the movement of air mass during winter months appear to originate from the


Time (IST)

2 4 6 8 10 12 14 16 18 20 22 24

Ave

rage

met

hane

(pp

mv)

0.0

0.5

1.0

1.5

2.0

2.5Winter Summer

Monsoon Post monsoon

(b)

2 4 6 8 10 12 14 16 18 20 22 24

C H

4 (p

pmv)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Methane

TN

MH

Cs (ppbv)

5

10

15

20

25

30

35

Total nonmerthane hydrocarbons

(a)

Fig. 7. (a) Seasonal average diurnal variations of CH4 (b) Annual average diurnal variations of CH4 and total NMHCs at KUC.

east of this observational site (continental air) that brought pollutants nearby industrialized region to the observational site. Low mixing ratios of CH4 and total NMHCs observed during monsoon season were mainly due to the reduction in atmospheric hydrocarbons because of the reduced photochemical reactions and the substantial reduction in solar intensity. Jobson et al., (1994) reported that alkane and acetylene hydrocarbons in total NMHCs displayed a winter maximum and summer minimum at a remote site in Canada. Hydrocarbon abundance was fairly well mixed over the winter time when NMHCs mixing ratios were much higher than during summer (Hakola et al., 2006). Seasonal variation in strong hydrocarbon source, differences in atmospheric behavior such as increased convection, vertical mixing in the summer and differences in air mass climatology with season, also play a vital role in the seasonal variation of hydrocarbon (Jobson et al., 1994). Hov et al. (1991) found a seasonal trend for ethene and propene with a late January maxima and minima during July-August. A recent study conducted in Ahmedabad (Lal et al., 2008) and Delhi (Pandit et al., 2011) revealed that total NMHC has a significant seasonal variation; with maximum concentrations in winter and low in late summer and in monsoon seasons. C2-C5 Hydrocarbons Measured in the Ambient Air

In order to retrieve the concentrations of C2-C5

hydrocarbons in ambient air, air samples were collected at five different locations in Kannur so as to represent different characteristics, such as rural/semi urban, paddy field, forest area, riverbank and traffic junctions. Table 3 summarizes the concentrations of prominent NMHCs measured at five different sites including KUC in Kannur during January and March 2012. Measured C2-C5 NMHC species were Acetylene/Ethyne (C2H2), Ethylene/ Ethene (C2H4), Ethane (C2H6), Propylene/propene (C3H6), Propane (C3H8), Butanes (C4H10) and Pentanes (C5H12).

Acetylene (C2H2) has common sources from combustion with mean lifetimes of about two weeks and it is removed from the atmosphere by reaction with the OH radicals. The air samples collected from KUC contained higher concentration of acetylene (139.84 ppbv) and that collected from the nearby river basin had a lower concentration of acetylene (4.08 ppbv). Surprisingly, air samples collected from all other locations did not exhibit the presence of acetylene. The enhanced concentration of acetylene observed during early morning at KUC is mainly due to its emission from the adjacent ceramic powder production unit which employs a high temperature furnace in which acetylene is used as gas to process the solid ceramic into its powder form. The furnace usually operates in the nighttime to get uninterrupted electric power in the unit. In the early morning, they used to flush out the gas for safety. But at the river basin,


Table 3. Concentrations of non-methane hydrocarbon in the ambient air at KUC and other locations in Kannur.

Compound

Locations and the concentration of NMHC in ppbv KUC Paddy field

Forest area 12 pm

River side 2 pm

Traffic Junction

5 pm 7 am 12 pm 7 pm 8 pm 11 am 5 pm

Acetylene 139.84 - - - - - - 4.08 - Ethylene - - 55.39 - 3.31 186.78 - - 4.31 Ethane - - - - 87.27 - - - 110.49

Propylene - - - - 2.51 - - - - Propane - - - - 9.54 - - - 17.30 i-Butane - - - - - 3.94 - - - n-Butane 2.49 - 41.71 1.77 6.13 48.84 - - 5.60 i-Pentane 20.78 18.0 78.74 28.11 36.85 71.50 - 32.55 36.77 n-Pentane 65.24 106.66 152.38 172.51 8.53 130.10 242.26

acetylene is present in the organic emission from the wet lands and nearby paddy fields. Further, acetylene is mostly from industrial or automobile sources and it reacts fairly rapidly during daytime. Ethylene (C2H4) is emitted into the atmosphere from a number of natural and anthropogenic sources. It is a potent regulator of plant growth and development and may have substantial effects at low concentrations in ambient air. Ethylene was abundant at KUC and nearby paddy field in the late afternoon at 17:00 h.

Ethane (C2H6) was the second most abundant organic trace gas in the background troposphere and it plays a crucial role in the chemistry of the lower atmosphere, chiefly through reactions with the OH radical. Ethane is primarily emitted to the atmosphere during mining, processing, transport and consumption of fossil fuels, during use of biofuels and during biomass burning. Further, it is mainly emitted from paddy fields where organic fertilizers are commonly used and has a seasonally varying lifetime (Blake and Rowland, 1986; Rudolph, 1995). In this analysis, the concentrations of ethane in the ambient air collected at traffic junctions (110.49 ppbv) and paddy field (87.27 ppbv) and were below the detectable limit in the other air samples. The enhanced emission at traffic junction is due to the intense vehicular activities during the peak hour at 5 pm.

Presence of propylene (C3H6) in the ambient air was found only at paddy field with a concentration of 2.5 ppbv in morning and propane (C3H8) concentrations was observed merely at paddy field (9.54 ppbv), traffic junctions (17.30 ppbv) and the existence of i-Butane was limited to paddy field alone in this investigation. N-Butane was found high (48.84 ppbv) in the paddy field at 17:00 h and minimum (2.49 ppbv) in KUC at 07:00 h. I-Pentane and n-Pentane were observed in all the air samples collected in different locations and it was found that concentration of i-pentane was found to be maximum (78.74 ppbv) at KUC and n-pentane was maximum (172.51 ppbv) in the paddy field. The quantification of these prominent organic species validates the abundance of VOCs that induce the production of surface O3 in the presence of NO2. Correlation between O3, CH4, NMHC and NMHC/NOx

A precise characterization of O3 and its precursors are useful for the analysis of O3 chemistry. The burning of

agricultural crop waste emits precursor gases such CH4, NO2, CO and hydrocarbons in this location. Fig. 8(a) represents the variation of O3 concentration with CH4 mixing ratio during the morning periods of winter season at the observational site. An excellent linear fit (p < 0.01) revealed the active photochemistry of O3 production associated with CH4. The empirical relationship is

[O3] = 3.28 + 0.002 [CH4] (4)

However, by noontime, with the active presence of sea

breeze influencing the site from the Arabian Sea, major part of CH4 is lost through reaction with OH as CH4 + OH CH3 + H2O (5)

Non-methane hydrocarbons (NMHCs) are abundant in

smoke resulting from biomass burning and have short atmospheric lifetimes. Total Nonmethane hydrocarbons (TNMHCs) in the atmosphere influence the climate through their production of organic aerosols and their involvement in O3 photochemistry. Mean concentrations of TNMHCs were relatively higher in winter than summer and monsoon. Though there was not much seasonal variability in emission sources, the variation in TNMHCs concentration during different seasons can be attributed to the OH radical chemistry in the atmosphere. TNMHC/NOx ratio was higher during daytime hours, which was mainly due to the increased emissions of hydrocarbons at the site. Oxidation of hydrocarbons in the atmosphere by OH leads to alkyl peroxy radicals and hydroperoxy radicals. The impact on O3 production is dependent not only ambient NOx, but more so on hydrocarbon to NOx ratio (TNMHC/NOx).

From the Fig. 8 (b), it is clear that surface O3 and [TNMHC]/[NOx] during daytime was linearly correlated with a correlation coefficient of 0.82. Non-methane hydrocarbons do not have secondary sources in the atmosphere; the atmospheric sources of these species are linked to the emission processes near the source regions. The correlation between CH4 and NMHCs are useful for unfolding their chemistry. Fig 8(c) shows the linear correlation plot of TNMHCs and CH4 with a correlation coefficient of 0.71 (p < 0.01) during winter season. This high correlation coefficient


(a)

(b)

[O3]= 3.28 +0.002 [CH4]

Correlation coefficient (r)= 0.86

[O3]= 2.56 +2.7 [TNMHC]/[NOx]

Correlation coefficient (r)= 0.82

[CH4]= 511 +79.93 [TNMHC]

Correlation coefficient (r)= 0.71(c)

Methane (ppbv)

1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8

Ozo

ne (

ppbv

)

6

7

8

9

10

[TNMHC]/[NOx]0 2 4 6 8 10 12 14 16 18 20

Ozo

ne (

ppbv

)

0

10

20

30

40

50

TNMHC (ppbv)

10 15 20 25 30 35

Met

hane

(pp

mv)

1

2

3

4

Fig. 8. Scatter plots showing the correlation between (a) ozone and methane (b) O3 and [NMHC]/[NOx] (c) NMHCs and CH4 over Kannur during winter season.

proposes that locally emitted TNMHCs and CH4 at KUC has a major role in active photochemistry during winter season.

Comparitive Obervations of Surface O3 at Ooty, a Free Tropospheric Region in Western Ghats

An attempt was made to study the diurnal variation of O3 in a free tropospheric region at Ooty lying in the Western Ghats region on clear sky days in February 2011 in order to get a glimpse of O3 variation along the east of Kannur. The location of observation site at Ooty is in the Nilagiris,

the queen of hills at 11.3°N latitude, 74.4°E longitude and at an altitude of 2240 m above mean sea level which is the same latitude of Kannur. Ooty is located along east of Kannur with an air distance of 140 km. The geography of Ooty is quite unique owing to its location nestled amidst the district of the Nilgiris mountain range which is home to Doddabetta peak, considered as the highest peak in south India. Being a hillock region, nighttime is typically chilly in the months of January and February. Temperatures are relatively consistent throughout the year; with average high temperatures ranging from about 17–20°C and average low temperatures in the range 5–12°C with annual average precipitation of 1250 mm. Measurements of surface O3 concentration at Doddabetta peak in Ooty were carried out on a few clear sky days in February 2011 and the diurnal variations of O3 is shown in Fig. 9. Lower O3 concentrations are observed during early morning and mid day time and they gradually increase to a maximum concentration till late evening and midnight hours. The minimum mixing ratio of O3 is 26.92 ppbv and maximum of 64.06 ppbv O3 concentrations are observed at 08:50 h and 19:00 h respectively. The average O3 concentration during day time (08:00 to 17:00 h) is 48.12 ppbv and night time (1700–0800 h) is 52.35 ppbv. Since Ooty is situated at a higher altitude, the height of the boundary layer plays a significant role on the mixing and transport of O3. After the sun rise, solar heating warms the air in the valley producing warm upslope winds. Hence, air reaching the mountain top may have had a long path of travel and thereby O3 loss can occur due to surface deposition.

After sunset, radiative cooling of the mountain surface cools the air adjacent to the surface, resulting in cold down slope winds. These winds bring air rich in O3 from aloft. Hence O3 concentrations gradually build up during late evening and mid night hours. The other tropical high altitude site Mt Abu (1680 m asl) also reported the strong effects of mountain induced wind flow patterns on the diurnal variations of O3 (Naja et al., 2003). Another high altitude site at Mauna Loa (3397 m asl) also reported the same outline (Oltmans and Kohhyr, 1986). Recent observations

Time (IST)

2 4 6 8 10 12 14 16 18 20 22 24

Ozo

ne (

ppbv)

0

10

20

30

40

50

60

70

80

Fig. 9. Diurnal variation of surface O3 at Ooty observed on clear sky days.


near Mount Everest by Moore and Semple (2009) reveal the presence of high levels of O3 at elevations from 5000-9000 m. They suggest that this mounting level of O3 is due to the descent of O3 rich stratospheric air as well as the long range transport of tropospheric pollutants from Southeast Asia. There may be a possibility of O3 transport from the regions of Western Ghats to the coastal locations in winter months because of the north easterly winds found to prevail over Kannur during the winter season.

CONCLUSION

There have been several studies of surface O3 and its precursors for different regions around the world and there is good evidence for an increase in the global surface level of O3 in the past century. This work was focused on the study of variability of surface O3 and its precursors (NOx, CH4 and total NMHC) that influenced the air quality over Kannur a tropical site confined between the coastal belt of Arabian Sea and Western Ghats. Diurnal variations of surface O3 and its precursor NOx were investigated since November 2009. Significant seasonal variations for O3 and NOx mixing ratios were observed at this site. The daily average diurnal variation of O3 showed a maximum mixing ratio in the late afternoon during all seasons due to its enhanced production by the photolysis of NO2 and minimum during early morning over a period of two years from November 2009 to December 2011. The average seasonal variations of O3 were observed to be maximum during winter and minimum during the monsoon period. During winter, both winds and atmospheric boundary layer depth are low and pollution hazards occurring during this season may contribute the observed high O3 mixing ratios at this location. However, during summer, in spite of higher solar flux, O3 concentration was low at this site. This may be due to cloud cover and the higher humidity near the Arabian Sea. The rate of production of O3 during morning was found to be higher in December and minimum in July. The rate of decrease of O3 during evening was found to be maximum in December and minimum in June. A good correlation was found between O3, NO and NO2 which revealed the chemistry of O3 production from NO2 and titration with NO at this location. The net effect of NOx on O3 concentrations was negative with a decaying exponential correlation indicating a possible VOC sensitive location, which showed the prominent role of abundant biogenic VOCs on the production of O3 even at lower levels of NO2. These observations were valuable in understanding the ambient air quality at a location with a high population density but in an industrially weak area. There is a need for a detailed chemistry transport model for understanding various physical, chemical and dynamical processes. The results of this study are preliminary and need confirmation with more detailed, continuous and systematic measurements of ozone and its precursors over this region to explore the O3 chemistry to improve the understanding of the chemical and dynamical processes and transport over this location. This will be further ascertained through a precise analysis of both indoor and outdoor air quality in this area.

ACKNOWLEDGEMENTS

The observations are carried out under the consistent financial support from ISRO-GBP through AT-CTM program. Authors are grateful to Professor Shyam Lal, Physical Research Laboratory Ahmadabad and Professor PPN Rao, ISRO, Bangalore for their keen interest in this programme. One of the authors, Nishanth expresses his gratitude to Indian Space Research Organization for awarding SRF under ISRO-GBP (AT-CTM) programme. The authors wish to thank professor Udayasooryan and his associates of TNAU for their support received at Ooty for ozone monitoring. Thanks are also due to Dr. Y.V. Swamy and his associates of IICT, Hyderabad for valuable help received in connection with the analysis of air samples. REFERENCES Alappattu, D.P., Kunhikrishnan, P.K., Aloysius, M. and

Mohan, M. (2009). A Case Study of Atmospheric Boundary Layer Features during Winter over a Tropical Inland Station -Kharagpur (22.32°N, 87.32°E). J. Earth Syst. Sci. 118: 281–293

Altimir, N., Kolari, P., Tuovinen, J.P., Vesala, T., Bäck, J., Suni, T., Kulmala, M. and Hari, P. (2006). Foliage Surface Ozone Deposition: A Role for Surface Moisture? Biogeosciences 3: 209–228

Alvarez, R., Weilenmann, M. and Favez, J.Y. (2008). Evidence of Increased Mass Fraction of NO2 within Real World NOx Emissions of Modern Light Vehicles Derived from a Reliable Online Measuring Method. Atmos. Environ. 42: 4699–4707.

Aneja, V.P., Businger, S., Li, Z., Ciaiborn, C.S. and Murthy, A. (1991). Ozone Climatology at High Elevations in the Southern Appalachians. J. Geophys. Res. 96: 1007–1021.

Beig, G., Gunthe, S. and Jadhav, D.B. (2007). Simultaneous Measurements of Ozone and Its Precursors on a Diurnal Scale at a Semi Urban Site in India. J. Atmos. Chem. 57: 239–253.

Blake, D.R. and Rowland, S.F. (1986). Global Atmospheric Concentrations and Source Strength of Ethane. Nature 321: 231–233.

Bonasoni, P., Laj, P., Angelini, F., Arduini, J., Bonafè, U., Calzolari, F., Cristofanelli, P. and Decesari, S. (2008). The ABC-Pyramid Atmospheric Research Observatory in Himalaya for Aerosol, O3 and Halocarbon Measurements. Sci. Total Environ. 391: 252–261.

Bossioli, E., Tombrou, M., Dandou, A. and Soulakellis, N. (2007). Simulation of the Effects of Critical Factors on O3 Formation and Accumulation in the Greater Athens Area. J. Geophys. Res. 112: D02309, doi: 10.1029/2006 JD007185.

Chameides, W.L. and Walker, J.C.G. (1973). A Photochemical Theory of Tropospheric Ozone. J. Geophys. Res. 78: 8751–8760, doi: 10.1029/JC078i036p08751

David, L.M. and Nair, P.R. (2011). Diurnal and Seasonal Variability of Surface Ozone and NOx at a Tropical Coastal Site: Association with Mesoscale and Synoptic Meteorological Conditions. J. Geophys. Res. 116: D10303,


doi: 10.1029/2010JD015076. Debaje, S.B., Jeyakumar, S.J., Ganesan, K. and Jadhav,

D.B. (2003). Surface O3 Measurements at Tropical Rural Coastal Station Tranquebar, India. Atmos. Environ. 37: 4911–4916.

Debaje, S.B. and Kakade, A.D. (2006). Measurement of Surface O3 in Rural Site of India. Aerosol Air Qual. Res. 6: 444–465.

Devara, P.C.S. and Raj, E.P. (1993). Lidar Measurements of Aerosols in the Tropical Atmosphere. Adv. Atmos. Sci. 10: 365–378.

Finlayson-Pitts, B.J. and Pitts Jr., J.N. (1986). Formation of Sulfuric and Nitric Acids in Acid Rain and Fogs. Atmospheric Chemistry: Fundamental and Experimental Techniques, John Wiley & Sons, New York, p. 702–705.

Ghude, S.D., Jain, S. L., Arya, B. C., Beig, G., Ahammed, Y.N., Kumar, A. and Tyagi, B. (2008). Ozone in Ambient Air at a Tropical Megacity, Delhi: Characteristics, Trends and Cumulative Ozone Exposure Indices. J. Atmos. Chem. 60: 237–252

Hakola, H., Hellen, H. and Laurila, T. (2006). Ten Years of Light Hydrocarbons (C2-C6) Concentration Measurements in Background air in Finland. Atmos. Environ. 40: 3621–3630.

Han, S., Bian, H., Feng, Y., Liu, A., Li, X., Zeng, F. and Zhang, X. (2011). Analysis of the Relationship between O3, NO and NO2 in Tianjin, China. Aerosol Air Qual. Res. 11: 128–139.

Hov, O., Schmidbauer, N. and Oehme, M. (1991). C2-C5 Hydrocarbons in Rural South Norway. Atmos. Environ. 25A: 1981–1999.

Jenkin, M.E. and Clemitshaw, K.C. (2000). Ozone and Other Secondary Photochemical Pollutants Chemical Processes Governing Their Formation in the Planetary Boundary layer. Atmos. Environ. 34: 2499–2527.

Jobson, B.T., Wu, Z. and Niki, H. (1994). Seasonal Trends of Isoprene, C2-C5 Alkanes and Acetylene at a Remote Boreal Site in Canada. J. Geophys. Res. 99: 1589–1599.

Klonecki, A., Hess, P., Emmons, L., Smith, L., Orlando, J. and Blake, D. (2003). Seasonal Changes in the Transport of Pollutants into the Arctic Troposphere-model Study. J. Geophys. Res. 108: 8367, doi: 10.1029/2002JD002199.

Kumar, R., Naja, M., Venkataramani, S. and Wild, O. (2010). Variations in Surface Ozone at Nainital, a High Altitude Site in the Central Himalayas. J. Geophys. Res. 115: D16302, doi: 10.1029/2009JD013715.

Lal, S., Sahu, L.K., Venkataramani, S. Rajesh, T.A. and Modh, K.S. (2008). Distributions of O3, CO and NMHCs over the Rural Sites in central India. J. Atmos. Chem. 61: 73–84.

Liu, Y., Shao, M., Fu, L., Lu, S., Zeng, L. and Tang, D. (2008). Source Profile of Volatile Organic Compounds (VOCs) Measured in China: Part I. Atmos. Environ. 42: 6247–6260.

Mahalakshmi, D.V., Badarinath, K.V.S. and Naidu, C.V. (2011). Influence of Boundary Layer Dynamics on Pollutant Concentrations over Urban Region-A Study Using Ground Based Measurements. Indian J. Radio Space Phys. 40: 147–152

Mahapatra, P.S., Jena, J., Moharana, S., Srichandan, H., Das, T., Roy C.G. and Das S.N. (2012). Surface Ozone Variation at Bhubaneswar and Intra-corelationship Study with Various Parameters. J. Earth Syst. Sci. 121: 1163–1175.

Mazzeo, A.N., Venegas, E.L. and Choren, H. (2005). Analysis of NO, NO2, O3 and NOx Concentrations Measured at a Green Area of Buenos Aires City during Wintertime. Atmos. Environ. 39: 3055–3068.

Moore, G.W.K. and Semple, J.L. (2009). High Concentration of Surface O3 Observed along the Khumbu Valley Nepal April 2007. Geophys. Res. Lett. 36: L14809, doi: 10.1029/2009GL038158

Nair, P.R., Chand, D., Lal, S., Modh, K.S., Naja, M., Parameswaran, K. Ravindran, S. and Venkataramani, S. (2002). Temporal Variations in Surface O3 at Thumba (8.6°N, 77°E) -A Tropical Coastal site in India. Atmos. Environ. 36: 603–610.

Naja, M. and Lal, S. (2002). Surface O3 and Precursor Gases at Gadanki (13.5°N, 79.2°E), a Tropical Rural Site in India. J. Geophys. Res. 107: ACH 8-1–ACH 8-13, doi: 10.1029/2001JD000357.

Naja, M., Lal, S. and Chand, D. (2003). Diurnal and Seasonal Variabilities in Surface O3 at a High Altitude Site Mt Abu (24.6°N, 72.7°E, 1680 m asl) in India. Atmos. Environ. 37: 4205–4215.

Nishanth, T., Ojha, N., Kumar, M.K.S. and Naja, M. (2011). Influence of Solar Eclipse of 15 January 2010 on Surface Ozone. Atmos. Environ. 45: 1752–1758

Nishanth, T., Praseed, K.M., Rathakaran, K., Kumar, M.K.S., Krishna, R.R. and Valsaraj, K.T. (2012a). Atmospheric Pollution in a Semi-urban, Coastal Region in India Following Festival Seasons. Atmos. Environ. 47: 295–306.

Nishanth, T., Kumar, M.K.S., Valsaraj, K.T. (2012b). Variations in Surface Ozone and NOx at Kannur: A Tropical, Coastal Site in India. J. Atmos. Chem. 69:101–126.

Nishanth, T., Praseed, K.M., Kumar, M.K.S. and Valsaraj, K.T. (2012c). Analysis of Ground level O3 and NOx Measured at Kannur, India. J. Earth Sci. Clim. Change 3: 111, doi: 10.4172/2157-7617.1000111.

Ojha, N., Naja, M., Singh, K. P., Sarangi, T., Kumar, R., Lal, S., Lawrence, M.G., Butler, T.M. and Chandola, H.C. (2012). Variabilities in Ozone at a Semi-urban Site in the Indo-Gangetic Plain Region: Association with the Meteorology and Regional Processes. J. Geophys. Res. 117: D20301, doi: 10.1029/2012JD017716.

Oltmans, S.J. (1981). Surface O3 Measurements in Clean Air. J. Geophys. Res. 86: 1174–1180.

Oltmans, S.J. and Komhyr, W.D. (1986). Surface O3 Distributions and Variations from 1973-1984, Measurements at the NOAA Geophysical Monitoring for Climatic Change Baseline Observatories. J. Geophys. Res. 91: 5229–5236.

Ordóñez, C., Brunner, D., Staehelin, J., Hadjinicolaou, P., Pyle, J. A., Jonas, M., Wernli, H. and Prevot, A.S.H. (2007). Strong Influence of Lowermost Stratospheric Ozone on Lower Tropospheric Background Ozone


Changes over Europe. Geophys. Res. Lett. 34: L07805, doi: 10.1029/2006GL029113.

Pandit, G.G. and Mohan Rao, A.M. (1990). Evaluation of Auto Exhaust Contribution to Atmospheric C2-C5 Hydrocarbons at Deonar, Bombay. Atmos. Environ. 24A: 811–813.

Pandit, G.G., Sahu, S.K. and Puranik, V.D. (2011). Distribution and Source Apportionment of Atmospheric Non Methane Hydrocarbons in Mumbai, India. Atmos. Pollut. Res. 2: 231–236.

Peleg, M., Luria, M., Sharf, G., Vanger, A., Kallos, G., Kotroni, V., Lagouvardos, K. and Varinou, M. (1997). Observational Evidence of an Ozone Episode over Greater Athens Area. Atmos. Environ. 31: 3969–3983.

Praveena, K. and Kunhikrishnan, P.K. (2004). Temporal Variations of Ventilation Coefficient at a Tropical Indian Station Using UHF wind Profiler. Curr. Sci. 86: 447–450.

Poberaj, S.C., Staehelin, J., Brunner, D., Thouret, V., de Backer, H. and Stübi, R. (2009). Long Term Changes in UT/LS Ozone between the Late 1970s and the 1990s Deduced from the GASP and MOZAIC Aircraft Programs and from Ozonesondes. Atmos. Chem. Phys. 9: 5343–5369.

Pudasainee, D., Sapkota, B., Shrestha, M.L., Kaga, A., Kondo, A. and Inoue, Y. (2006). Ground Level O3 Concentrations and Its Association with NOx and Meteorological Parameters in Kathmandu Valley, Nepal. Atmos. Environ. 40: 8081–8087.

Qin, Y., Tonnesen, G.S. and Wang, Z. (2004). One-hour and Eight-hour Average O3 in the California South Coast Air Quality Management District: Trends in Peak Values and Sensitivity to Precursors. Atmos. Environ. 38: 2197–2207.

Ramana, M.V., Praveena, K., and Kunhikrishnan, P.K. (2004). Surface Boundary Layer over a Tropical Inland Region: Seasonal Features. Boundary Layer Meteorol. 111: 153–175.

Rao, T.V.R., Reddy, P.R., Sreenivasulu, R., Peeran, S.G., Murthy, K.V.N., Ahammed, Y.N., Gopal, K.R., Azeem, P.R., Sreedhar, B. and Sunitha, K. (2002). Air Space Pollutants CO and NOx Levels at Anantapur (Semi-arid Zone), Andhra Pradhesh. J. Indian Geophys. Union 3: 151–161.

Reddy, B.S.K., Kumar, R.K., Balakrishnaiah, G., Rama Gopal, K., Reddy, R.R., Ahammed, Y.N., Narasimhulu, K., Reddy, S.S.L. and Lal, S. (2010). Observational Studies on the Variations in Surface O3 Concentration at Anantapur in Southern India. Atmos. Res. 98: 125–139.

Reddy, K.K., Naja, M., Ojha, N., Mahesh, P. and Lal, S. (2012). Influences of the Boundary Layer Evolution on Surface Ozone Variations at a Tropical Rural Site in India. J. Earth Syst. Sci. 121: 911–922.

Rehme, K.A. (1976). Application of Gas Phase Titration in the Calibration of Nitric Oxide, Nitrogen Dioxide and Ozone Analyzers, Calibration in Air Monitoring. ASTM STP 598, American Society for Testing and Materials, p. 198–209.

Rudolph, J. (1995). The Tropospheric Distribution and Budget of Ethane. J. Geophys. Res. 100: 11369–11381.

Ryerson, T.B., Trainer, M., Holloway, J.S., Parrish, D.D.,

Huey, L.G., Sueper, D.T., Frost, G.J., Donnelly, S.G., Schauffler, S., Atlas, E.L., Kuster, W.C., Goldan, P.D., Huebler, G., Meagher, J.F. and Fehsenfeld, F.C. (2001). Observations of Ozone Formation in power Plant Plumes and Implications for Ozone Control Strategies. Science 292: 719–723.

Saito, S., Nagao, I. and Tanaka, H. (2002). Relationship of NOx and NMHC to Photochemical O3 Production in Coastal and Metropolitan Areas of Japan. Atmos. Environ. 36: 1277–1286

Seinfeld, J.H. and Pandis, S.N. (2006). Atmospheric Chemistry and Physics from Air Pollution to Climate Change, John Wiley and Sons, New York.

Shan, W., Yin, Y., Zhang, J. and Ding, Y. (2008). Observational study of Surface O3 at an Urban Site in East China. Atmos. Res. 89: 252–261.

Shan, W., Yin, Y., Zhang, J., Ji, X. and Deng, X. (2009). Surface Ozone and Meteorological Condition in a Single Year at an Urban Site in Central Eastern China. Environ. Monit. Assess. 151: 127–141.

Shao, M., Zhang, Y., Zeng, L., Tang, X., Zhang, J., Zhong, L. and Wang, B. (2009). Ground Level Ozone in the Pearl River Delta and the Roles of VOC and NOx in Its Production. J. Environ. Manage. 90: 512–518.

Sharma, P., Kuniyal, J.C., Chand, K., Guleria, R.P., Dhyani, P.P. and Chauhan, C. (2013). Surface Ozone Concentration and Its Behaviour with Aerosols in the Northwestern Himalaya, India. Atmos. Environ. 71: 44–53.

Singla, V., Satsangi, A., Pachauri, T., Lakhani, A. and Kumari, K.M. (2011). O3 Formation and Destruction at a Sub-urban Site in North Central Region of India. Atmos. Res. 101: 373–385.

Solberg, S., Hov, Ø., Søvde, A., Isaksen, I.S.A., Coddeville, P., De Backer, H., Forster, C., Orsolini, Y. and Uhse, K. (2008). European Surface O3 in the Extreme Summer 2003. J. Geophys. Res. 113: D07307, doi: 10.1029/2007 JD009098.

Song, F., Shin, J.Y., Atresino, R.J. and Gao, Y. (2011). Relationships among the Springtime Ground-level NOx, O3 and NO3 in the Vicinity of Highways in the US East Coast. Atmos. Pollut. Res. 2: 374–383.

Stephens, S., Madronich, S., Wu, F., Olson, J.B., Ramos, R., Retama, A. and Muñoz, R. (2008). Weekly Patterns of México City’s Surface Concentrations of CO, NOx, PM10 and O3 during 1986–2007. Atmos. Chem. Phys. 8: 5313–5325.

Sun, Y., Wang, L., Wang, Y., Quan, L. and Zirui, L. (2011). In Situ Measurements of SO2, NOx, NOy, and O3 in Beijing, China during August 2008. Sci. Total Environ. 409: 933–940.

Swamy, Y.V., Nikhil, G.N., Venkanna, R., Chitanya Dhulipala, N.S.K., Sinha, P.R., Srinavasan, S. and Anupoju, G.R. (2013). Role of Nitrogen Oxides, Black Carbon, and Meteorological Parameters on the Variation of Surface Ozone Levels at a Tropical Urban Site-Hyderabad India. Clean-Soil Air Water 41: 215–225.

Volz, A. and Kley, D. (1988). Evaluation of the Montsouris Series of O3 Measurements Made in the Nineteenth Century. Nature 332: 240–242, doi: 10.1038/332240a0.


Wang, T., Wei, X.L., Ding, A.J., Poon, C.N., Lam, K.S., Li, Y.S., Chan, L.Y. and Anson, M. (2009). Increasing Surface Ozone Concentrations in the Background Atmosphere of Southern China, 1994–2007. Atmos. Chem. Phys. 9: 6217–6227.

Wesely, M.L. (1989). Parameterization of Surface Resistances to Gaseous Dry Deposition in Regional-scale Numerical Models. Atmos. Environ. 23: 1293–1304.

Wesely, M.L., Hicks, B.B. (2000). A Review of the Current Status of Knowledge on Dry Deposition. Atmos. Environ. 34: 2261-2282

Winer, A.M., Peters, J.W., Smith, J.P. and Pitts Jr., J.N. (1974). Response of commercial Chemiluminescent NO-NO2 Analyzers to Other Nitrogen Containing Compounds. Environ. Sci. Technol. 8: 1118–1121.

Yarwood, G., Grant, J., Koo, B. and Dunker, A.M. (2008). Modeling Weekday to Weekend Changes in Emissions and O3 in the Los Angeles Basin for 1997 and 2010. Atmos. Environ. 42: 3765–3779.

Yin, Y., Shan, W., Ji, X., Deng, X., Cheng, J. and Li, L. (2010). Analysis of the Surface Ozone during Summer and Autumn at a Coastal Site in East China. Bull. Environ. Contam. Toxicol. 85: 10–14.

Zerefos, C., Kourtidis, K.A., Melas, D., Balis, D., Zanis, P., Katsaros, L., Mantis, H.T., Repapis, C., Isaksen, I., Sundet, J., Herman, J., Bhartia, P.K. and Calpini, B. (2002). Photochemical Activity and Solar Ultraviolet Radiation Modulation Factors (PAUR): An Overview of the Project. J. Geophys. Res. 107: D18, doi: 10.1029/2000 JD000134.

Zhu, T., Lin, W., Song, Y., Cai, X., Zou, H., Kang, L., Zhou, L. and Akimoto, H. (2006). Downward Transport of O3 Rich Air near Mt. Everest. Geophys. Res. Lett. 33: L23809, doi: 10.1029/2006GL027726.

Received for review, November 22, 2012 Accepted, September 3, 2013

Observational Study of Surface O3, NO , CH4 and Total ...A CH4 buildup was observed during early...

Documents

Transcript of Observational Study of Surface O3, NO , CH4 and Total ...A CH4 buildup was observed during early...