Final Report California Regional PM10/PM2.5 Air Quality Study ...
Influence of Sea Breeze_BC, PM2.5, PM10
Transcript of Influence of Sea Breeze_BC, PM2.5, PM10
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Influence of sea breeze circulation and road traffic emissions on therelationship between particle number, black carbon, PM1, PM2.5 andPM2.510 concentrations in a coastal city
Sergio Rodrguez a,b,*, Emilio Cuevas a, Yenny Gonzalez a, Ramon Ramos a,Pedro Miguel Romero a, Noem Perez c, Xavier Querol c, Andres Alastuey c
a Izana Atmospheric Research Centre, AEMet, Associated Unit to CSIC Studies on Atmospheric Pollution, C/ La Marina, 20,
6a Planta, E38001 Santa Cruz de Tenerife, Canary Islands, Spainb Department of Geology, University of Huelva, Associated Unit to CSIC on Air Pollution, Campus El Carmen, E21071 Huelva, Spainc Institute of Earth Science Jaume Almera, CSIC, Lluis Sole i Sabaris S/N, E08028 Barcelona, Spain
a r t i c l e i n f o
Article history:
Received 19 February 2008
Received in revised form 26 March 2008
Accepted 2 April 2008
Keywords:
Ultrafine particles
New particle formation
Black carbonSoot
Vehicle exhausts
a b s t r a c t
The physical characterisation of metrics representative of ambient air particle concentra-
tion is becoming a topic of great interest for urban air quality monitoring and human ex-
posure assessment. In this article, the influence of sea breeze circulation and primary road
traffic emissions on the relationship between the urban aerosol number (N3, particles
>3 nm), black carbon
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aerodynamic diameter, respectively) with an increased risk
to sufferers of respiratory and cardiovascular diseases
(Dockery and Pope, 1996). As a result of this, PM10 and
PM2.5 are currently used as urban air quality reference
metrics. More recent research has highlighted the high
potential toxicity of some PM components. For example, ul-
trafine particles (
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2. Methodology
2.1. Study city
This study was performed in Santa Cruz de Tenerife (Ca-
nary Islands; 28280N, 16150W; Fig. 1). This is a 221,500
inhabitant city (distributed over 150 km2) located at the
bottom of the southern slope of the Anaga ridge and the
eastern slope of the SW to NE ridge crossing the Island.
This topographic setting protects the city from the Trade
winds (NNE) that blow over the ocean (see details on the
meteorology in Guerra et al., 2004). The main sources of an-
thropogenic aerosols in the cityare: (1) road traffic (the two
main city roads are highlighted in Fig.1A), (2) a crude oil re-
finery (COR) located on the SE shore of the city (see COR in
Fig. 1C), and (3) ship emissions in the harbour. Natural
Saharan dust and sea salt may significantly contribute to
the daily aerosol load (>100 mgPM10 m3 during dust
events; Viana et al., 2002).
2.2. Measurements
Measurements of PM were performed simultaneously
(mid-March to mid-April 2006) at three sites in the city
of Santa Cruz de Tenerife (Fig. 1C): (1) Santa Cruz Observa-
tory (SCO), (2) Tome Cano (TC) and (3) Gladiolos (GL).
(A) Santa Cruz Observatory (SCO; Fig.1C) is a coastal urban
background site located on the roof of an 8-floor build-
ing at 52 m above sea level, at about 45 m above
ground. Measurements of meteorological parameters
(wind speed and direction, temperature, relative
humidity, pressure and global radiation), trace gases
(CO, SO2 and O3) and particles at SCO are performed
by the staff of Izana GAW Observatory in the frame-
work of the GURME (GAW) program. The site is on
the NE edge of the city, close to the shore and on the
western side of Anaga Avenue (a 4-lane road running
along the shore). The main data set used in this study
was collected at this site, where the following mea-
surements were performed:B PMx mass concentrations. One-minute concentrations of
PM1, PM2.5 and PM10 have been obtained at this site
since 2002 by multiplying the aerosol volume concen-
trations (monitored with an Optical Particle Counter
OPC GRIMM) by experimentally determined vol-
ume-to-mass conversion factors. These factors were
determined by cross correlating the aerosol (PM10 and
PM2.5) mass (determined by 24-h filter sampling with
high volume samplers) versus the volume (
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(B) Gladiolos and Tome Cano are city centre sites located to
the NWof the industrial area of the city (crude oil refin-
ery) and to the NW of the motorway (which links the
city to the northern side of the island; Fig. 1C). At these
sites measurements of PM10, PM2.5, gaseous pollut-
ants (CO, NOx, SO2 and O3) and meteorology (wind
speed and direction, temperature, relative humidity
and pressure) are continuously performed by following
standard procedures in air quality networks. Measure-
ments of PM10 and PM2.5 were performed with beta
and TEOM instruments, respectively. PM2.5 was not
monitored at the Tome Cano site.
Finally, measurements of road traffic intensity (number
of vehicles h1) were also performed in several parts of the
city by city council staff. In this article we will only show the
road traffic intensity at the coastal Anaga Avenue (where
the SCO site is located).
3. Results and discussion
During the intensive field measurement campaign,
mean concentrations of 24 mg m3 of PM10, 14 mg m3 of
PM2.5, 9 mg m3 of PM1, 1.9 mg m3 of BC and 26305
cm3 of N3 were recorded at the urban background SCO
site (Santa Cruz Observatory), 46 mg m3 of PM10 at TC
(Tome Cano) and 43 mg m3 of PM10 and 13 mg m3 of
PM2.5 at GL (Gladiolos) were recorded at the city centre
sites. These mean PMx concentrations are slightly lower
than the annual mean PMx concentrations typically
recorded in this city because Saharan dust events (the
main cause of high PMx concentrations in this city; Viana
et al., 2002) did not occur during our campaign. Thesemean PMx concentrations are within the range of those
typically observed in mid European cities (Harrison and
Jones, 2005; Puustinen et al., 2007; Rodrguez et al.,
2007; Ruuskanen et al., 2001).
3.1. Mean daily evolution of aerosols
The urban scale transport of air pollutants in Santa Cruz
de Tenerife is mainly driven by breeze circulation (Fig. 1B
and C). This breeze is characterised by inland (westward)
airflows during daylight (34 m s1) and a slight seaward
(eastward) airflowat night (w1 m s1). Inland breeze blow-
ing started at 08:00 and was characterised by an abrupt
shift in wind direction. Fig. 2 displays the regular daily evo-
lution of the road traffic intensity and the particle and some
gaseous pollutant concentrations at the SCO coastal
(Fig. 2AF), TC and GL city centre (Fig. 2GI) sites.
At the SCO coastal site, particle (PMx, BC and N3)and CO
concentrations exhibited a maximum during the morning
rush hours of working days, and a subsequent decrease
(09:0019:00) associated with the easterly entry of marine
air (Fig. 2AF). At night, a smooth increase in the PMx con-
centrations, associated with slight westerly winds bringing
air masses from the city centre, was observed at SCO.
At the TC and GL city centre sites, after the maximum in
the NO and PMx concentrations recorded during the
morning rush hours, a decrease in the PMx concentrations
such as that described above at SCO (09:0019:00) was not
observed (Fig. 2GI). However, PM10 and PM2.5 at TC and
GL showed an increasing trend until 21:00 (local time).
This contrasting behaviour between the PMx concentra-
tions at the coastal (SCO) and city centre (TC and GL) sites
is a consequence of the easterly inland breeze blowing dur-
ing daylight, which prompts the entry of clean marine air
masses along the coast and favours the inland transport of
the pollutants (emitted in the eastern part of the city) to the
city centre. This is one of the reasons because PM10 con-
centrations are much lower at SCO coastal than at TC and
GL city centre sites. In fact, this daylight breeze results in
the inland transport of the (refinery) SO2 plumes, giving
rise to higher SO2 concentrations during daylight than at
night at the TC and GL city centre sites (Fig. 2GI).
At the SCO coastal site, N3 and BC concentrations also
exhibited well defined daily cycles (Fig. 2AC). During
working days, N3 and BC presented a maximum during
the morning rush hours. The morning maximum in the
vehicles h1/wind speed ratio indicates that the morning
maximum in the particle concentration is favoured by the
coupled effects of an increase in the road traffic intensity
and low wind speed in the morning (owing to the fact
that the inland breeze has not yet started blowing). Observe
that the daily evolution of N3 and BC during weekdays is
different from that recorded at weekends because of the
change in road traffic patterns. This daily evolution in num-
ber concentration is similar to that typically observed in
other cities (e.g.Wehner and Wiedensohler, 2003; Charron
and Harrison, 2003; Rodrguez et al., 2007). In Helsinki and
Liepzig, a similar daily evolution in the black carbon mass
and soot number concentrations has been observed,
respectively (Pakkanen et al., 2000; Rose et al., 2006).
3.2. Processes af fecting urban coastal aerosol concentrations
The relationship between road traffic intensity,
meteorology and particle concentration at SCO (coastal
urban background site) was examined using Principal
Component Analysis (PCA) followed by a varimax rota-
tion. This analysis was performed at several times of
the day: morning (07:0009:00), central daylight
(11:0017:00) and night (00:0005:00). Three principal
components, accounting for 81, 66 and 72% of the total
variance for the three daytime periods selected, were
found (Table 1):
B principal component 1 is positively correlated with PMx
and BC and negatively correlated with wind speed.
The fact that this component does not exhibit a signifi-
cant correlation with road traffic intensity (number of
vehicles h1) indicates that fresh road traffic emissions
do not exhibit a major influence on PMx variance. The
significant negative factor loading of wind speed indi-
cates that this component accounts for the influence
on the aerosol mass (BC and PMx), of the dilution and
the air mass renovation prompted by wind blowing
over the study city. The negative association of the N3/
BC ratio in this component will be discussed later.
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B principal component 2 is positively correlated with road
traffic intensity, BC and N3. This component represents
the influence of fresh vehicle exhaust emissions on the
particle concentration.
B principal component 3 is present during daylight (i.e.
morning rush hours 07:0009:00 and central daylight
period 11:0017:00). The positive correlation of the
N3/BC ratio and solar radiation intensity suggests that
nucleation of photo-oxidized vapours contributes to in-
creasing the above ratio by enhancing new particle for-
mation in ambient air. Further details are provided
below.
3.3. Influence of wind speed
The results of the PCA shown above indicate that wind
speed exerts: (1) a major influence on PMx, (2) a moderate
influence on BC and (3) a relatively low influence on N3. In
fact, wind speed exhibited Pearsons correlation coefficients
(r) of0.50, 0.44, 0.41, 0.33 and 0.0 with PM2.510,
PM2.5, PM1, BC and N3, respectively (values calculated using
3092 10-min observations). These results are corroborated
when analysing the particle concentration versus wind
speed plots shown in Fig. 3. The fact that high N3 concentra-
tions (>45103 cm3) may still be recorded under high
wind speed conditions (>5 m s1) may be accounted for by
new particle formation processes. At a roadside site in Lon-
don, Charron and Harrison (2003) found that increases in
wind speed produced much higher decreases in the concen-
tration of accumulation mode particles (0.11 mm) than in
the concentration of nucleation mode particles (
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This behaviour is not observed for PM2.5 and PM1 (Fig. 4C1
and D1). During the morning, the PM2.510 concentrations
also tend to increase when road traffic intensity increases,
this being most probably due to road dust re-suspension
(Fig. 4E1).
The much lower direct influence of the road traffic
emissions in PM2.5 and PM1 (Fig. 4C1 and D1) than in N3
and BC (Fig. 4A1 and B1) may be accounted for by the com-
ing into force of the European Standards EURO 14 (pro-
gressively since 1992) for vehicle exhaust emissions.
Because these standards are established in terms of parti-
cle mass (g km1), they have decreased the emissions of
accumulation (0.11 mm) and coarse (>1 mm) mode parti-
cles, which are the main contributors to PMx. In contrast,
N3 and BC tend to increase when the road traffic intensity
increases. This is due to the fact that vehicle exhaust mostly
emits ultrafine and soot particles and these are the main
contributors to N3 and BC (Burtscher, 2005; Harris and
Maricq, 2001; Rose et al., 2006).
Although BC concentrations tend to increase when road
traffic intensity increases, different BC concentrations are
observed for a given number of vehicles h1 bin at different
times of the day (Fig. 4A1). For example, a road traffic inten-
sity within the range of 11001200 vehicles h1 is associ-
ated with 3.7 mgBC m3 during the 07:0009:00 period
and with 1.5 mgBC m3 during the 11:0017:00 period.
The lower BC concentrations during the 11:0017:00 pe-
riod are a consequence of the higher wind speeds during
that period of daylight (because of the inland breeze blow-
ing). For this reason we have normalized the road traffic in-
tensity data by dividing them by wind speed (Fig. 4A3).
Observe how BC concentrations tend to increase in
a more regular way (monotonic growth) when increasing
the vehicles h1/wind speed ratio than when increasing
the vehicles h1 ratio (Fig. 4A1 and A3). The results show
how increases in 200 vehicles h1 m1 s1 are associated
with BC increases of about 0.50 0.29 mgBC m3 (on aver-
age) at any time of the day.
This analysis of particle concentration versus vehi-
cles h1/windspeed was also applied tothe PMx andN3con-
centrations (Fig. 4A3F3). The most important results are:
(1) N3 also exhibits an increasing trend with the vehi-
cles h1/wind speed ratio of about 3250 2395 cm3
every 200 vehicles h1 m.s1 during the 07:0009:00
period and of about 65231437 cm3 every 200 vehi-
cles h1 m.s1 in the 11:0017:00 period. These higher
values in the 11:0017:00 period in comparison with
the 07:0009:00 period suggest an enhancement in
the particle formation processes at noon and during
the afternoon. This interpretation is supported by the
results shown in the following section.
(2) PM2.5 and PM1 do not exhibit a strong association with
the vehicles h1/wind speed ratio (as that described for
BC and N3).
(3) PM2.510 exhibits a clearly increasing trend of about
1.20 0.90 mgPM2.510 m3 every 200 vehicles h1
m.s1 during the morning rush hours (07:0009:00),
most probably due to road dust re-suspension. The
weaker association observed during the 11:0017:00
period (Fig. 4E3) is probably due to the influence of
sea salt transported inland during daylight.
3.5. The numbertoblack carbon ratios
The relationship between N3 and BC concentrations at
the SCO site has been used to identify periods of enhance-
ment in the new particle formation rates, which would lead
to an increase in the N3/BC ratio. At SCO, N3 and BC
exhibited a significant correlation because of the vehicle
exhaust emissions: r0.70 during the whole measure-
ments campaign (based on 3092 10-min averages data).
When plotting the N3 versus BC data, it can clearly be ob-
served that all points are comprised between two well
defined borders with slopes (S) Smin 4.8 106 parti-
cles ngBC1 and Smax 47106 particles ngBC1, repre-
senting the minimum and maximum N3/BC ratios
observed in ambient air at the SCO site, respectively
(Fig. 5). The fact that the N3 versus BC data are comprised
between these two slopes is observed at any time of the
day. For the periods 00:0005:00, 07:0009:00 and
11:0017:00, Smin and Smax exhibit values of 4.5, 4.9 and
8.1106 particles ngBC1 and 48, 43 and 57 parti-
cles ngBC1, respectively (plots not shown for the sake of
brevity). The fact that the slope Smin is much higher during
the central part of daylight, indicates that: (1) the slope Sminis strongly related to the minimum contribution of the ve-
hicle exhaust emissions to the particle number
Table 1
Factor loading of the Principal Components Analysis performed with data from selected periods
Morning rush hours (07:0 009:0 0) Central daylight (11:0 017:0 0) Night (0 0:0 005:0 0)
PC 1 PC 2 PC 3 PC 1 PC 2 PC 3 PC 1 PC 2
Vehicles h1 0.11 0.89 0.14 0.29 0.51 0.04 0.01 0.85
BC 0.56 0.70 0.33 0.39 0.82 0.22 0.75 0.59
N3 0.17 0.90 0.07 0.32 0.81 0.28 0.30 0.80
N3/BC 0.50 0.05 0.61 0.23 0.18 0.77 0.77 0.04
PM1 0.95 0.06 0.07 0.86 0.27 0.08 0.86 0.36PM2.5 0.96 0.04 0.08 0.89 0.21 0.05 0.86 0.37
PM2.510 0.88 0.16 0.08 0.52 0.16 0.55 0.85 0.46
Wind speed 0.42 0.15 0.81 0.63 0.07 0.12 0.49 0.09
Radiation 0.24 0.03 0.73 0.08 0.20 0.72
Explained variance 38% 24% 19% 29% 20% 17% 46% 26%
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concentration (minimum amount of particles emitted and
formed during the dilution and cooling of exhaust per
nanogram of BC emitted by the vehicle exhaust), and (2)
there is an enhancement in the new particle formation
rates during daylight resulting in a higher N3/BC ratio
(4.9106 particles ngBC1 during the 07:0009:00 period
and 8.1106 particles ngBC1 during the 11:0017:00 pe-
riod on average; Fig. 6). Observe in Fig. 6 how the N3/BC
ratio exhibits a daily evolution with a maximum during
daylight. Previous studies have shown that enhancements
in the new particle formation rates during the dilution
and cooling of the vehicle exhaust are favoured by low am-
bient air temperature (e.g. Olivares et al., 2007) and/or low
wind speed leading to less dilution (Casati et al., 2007).
However, these two reasons are not plausible at SCO, where
the highest N3/BC ratios are observed during the period of
highest temperature and wind speed 11:0017:00 (Fig. 6).
At SCO the N3/BC ratio reaches the highest values during
the noon and afternoon period when:
(1) solar radiation intensity reaches the highest values. In
fact, in the PCA discussed above, it was shown how
Principal Component 3 is correlated with the N3/BC ra-
tio and the solar radiation (PC 3 in Table 1),
(2) PM1 and PM2.5 concentrations (where most of the
aerosol surface area is comprised) are minima (Figs. 2
and 6). The fact that the N3/BC ratio exhibited a much
higher anti-correlation with PM1 and PM2.5 than
with PM2.510 during the 11:0017:00 period (plot
not shown), suggests a more active role of the accumu-
lation mode particles (which typically accounts for
most of the aerosol surface area) as condensation sink
for the aerosol gaseous precursors,
(3) it is positively correlated with wind speed for wind
speed values between 0 and 4 m s1 (Figs. 3E and 4F3).
These features suggest that, in additionto thenew particle
formation during the dilution and cooling of the vehicle ex-
haust, there is a non-negligible contribution to N3 concentra-
tions due to new particle formation in ambient air. In fact, the
features described above fit very well with those of the new
particle formation in ambient air described by Boy and Kul-
mala (2002), Rodrguez et al. (2005) and Hamed et al.
(2007). The behaviour observed at the SCO site indicates
that the decrease in PM1 and PM2.5 concentrations, promp-
ted by the increase in wind speed (due to the inland breeze
blowing), resultsin a decrease in theaerosol surface areacon-
centrations. This would favour nucleation, rather than con-
densation onto pre-existing particles, for those aerosol
gaseous precursors formed by photo-oxidation processes.
Observe in Fig. 6 how the daily variation of the N3/BC ratio
is much better modulated by the daily evolution of the in-
verse of PM1 (which typically comprises most of the aerosol
surface) thanby the daily evolution of PM2.5101. Anexam-
ple of one of these events (8th April 2006) is shown in Fig. 7:
observe the correlated increases in the N3/BC ratio and in so-
lar radiation intensity from 10:00 to 16:00. This contribution
to N3 due to nucleationin ambient airduring thecentral part
of the daylight accounts for: (1) the faster decrease in the BC
than in the N3 concentrations after the morning rush hours
(Fig. 2 A), and (2) the higher increase in N3 concentrations
for every 200 vehicles h1 m.s1 bin during the 11:00
17:00 period than during the 07:0009:00 period (described
above; 3250 cm3 during the 07:0009:00 and about
6523 cm3 during the 11:0017:00 periods).
0
40
20
6 8
N3/BC,106,
/ng
0
6
0
20
10
PM2.5-10,g/m3
0
40
20
PM2.5,g/m3
0
90
45
N
3103,cm-3
y = 1.87x-0.38
R2 = 0.120
y = 14.9x-0.21
R2
= 0.323
y = 5.68x-0.59
R2 = 0.524
20 4 10
wind speed, m/s
12
BC,g/m3
A
B
C
D
E
Fig. 3. Concentration of particles (AD) and N3/BC ratio (E) versus wind
speed at the SCO site. Red dots and line in plots D and E represent the
mean N3 and N3/BC values for each 1 m s1 bin.
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3.6. Day-to-day particle events
Fig. 8 shows the hourly BC, N3 and PMx concentrations
at the SCO site and the road traffic intensity during a period
of the measurement campaign. Fig. 9 shows the median of
the BC, N3 and PMx concentrations for each wind direction
for the 07:0009:00,11:0017:00 and 00:0005:00 periods
during all the measurement campaigns. These data (Figs. 8
and 9) clearly illustrate how N3, BC and PMx are influenced
in different ways by breeze circulation, vehicle exhaust
emissions and ageing processes given that:
1. high BC and N3 concentrations are recorded during the
morning rush hours due to fresh vehicle exhaust emis-
sions (07:0009:00; Figs. 8A,B and 9A,B), the highest be-
ing BC and N3 concentrations registered when wind
blows from the city centre (Southwest; Fig. 9A1) or
from the coastal Anaga Avenue (East; Fig. 8A1);
2. high N3 concentrations (associated with high N3/BC ra-
tios) during the central part of daylight (11:0017:00)
are associated with easterly winds (inland breeze;
Fig. 9B2) due to the above described new particle forma-
tion in ambient air (Figs. 6 and 9A2,B2). Examples of
wind speed, m/svehiclesh-1 vehiclesh-1/ wind speed, s/m
4
8
0
BC,g/m3
2400
2000
0
10
5
0
20
PM2.5-10,g/m3
10
15
0
PM2.5,g/m3
PM1,g/m3
0-5h
7-9h
11-17h
C2 C3C1
N3/BC,
106/ng
0
10
20
F2 F3F1
A2 A3A1
D2 D3D1
0
30
60
103N3,m-3
B2 B3B1
1200
1600
0
4 6 800 4
00
800
1200
1600
2000
2400
E2 E3E1
10
800
20
Fig. 4. Particle concentration and N3/BC ratio averaged for each 100 vehicles h1 bin (A1F1), for each 1 ms1 bin (A2F2) and for each 200 vehicles h1
bin (A3F3).
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these events occurred during the periods 2224 and 28
31 March 2006, when N3/BC ratios of 1525 106 parti-
cles ngBC1 and 3 nm) and PMx (PM1, PM2.5 and PM2.510) concen-
trations. BC and N3 concentrations are greatly influenced
by fresh vehicle exhaust emissions and exhibit an increas-
ing trend when the road traffic intensity (vehicles h1)/
wind speed ratio increases. In contrast, PMx (specially
PM1 and PM2.5) reaches the highest values at night due
to the seaward transport of aged particulate pollutants to
the shore, and the lowest values during daylight due to
the inland entry of clean marine air. Although N3 and BC
concentrations exhibit a significant correlation throughout
0
20
500
1000
10
30
4 8 12 16 200
globalradiation,w
/m2
time of day
0
N3 / BC, 106/ng
50PM2.5-10-1, m3/g
wind speed, m/s
125PM1-1, m3/g
Fig. 6. Daily mean cycle (hourly averaged values) of the global radiation,
wind speed, the N3/BC ratio, and the inverse of the PM1 (PM1
1
) andPM2.510 (PM2.5101) concentrations.
0
35103
10BC,ng/m3
70103
N3,cm-3
500
0
35103
70103
1000
0
Radiation,w/m2
0
15
30 N3/BC,106/ng
6 12 18
time of day
0
A
B
Fig. 7. 10-min averaged values of the solar radiation, N3/BC ratio, black car-
bon (BC) and number N3 concentrations at the SCO site during 8th April
2006.
120
50103
0
100103
BC, g/m3
N3,cm-3
Smin
Smax
6
Fig. 5. Hourly averaged values of the particle number N3 versus particle
black carbon (BC) concentrations at the SCO site.
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the whole day, the N3/BC ratio experiences a daily evolu-
tion correlated with that of the solar irradiance and wind
speed, in such a way that high N3 concentrations associated
with high N3/BC ratios and high solar irradiance conditions
are recorded during the daylight inland breeze period
due to an enhancement of some new particle formation
processes. The analysis performed indicates that this en-
hancement in the new particle formation processes is
strongly related to the nucleation of photo-oxidized va-pours under the relatively low PMx (and consequently
low aerosol surface area) concentrations prompted by the
inland entry of clean marine air due to the daylight breeze
blowing. The statistical tools used in this study corroborate
the association between BC and N3 with road traffic inten-
sity (fresh emissions), PMx and wind speed1 and N3/
BC ratio and solar radiation (enhancement in the new par-
ticle formation due to photo-oxidation processes).
Although it is known that new particle formation due to
photo-oxidation of aerosol gaseous precursors may occur
in the urban atmosphere (e.g. Wehner and Wiedensohler,
2003; Kulmala et al., 2004; Qian et al., 2007), most studieson urban ultrafine particles are currently focused mainly
on primary vehicleexhaust emissions. The resultsobtained
here indicate that this contribution due to photo-chemically
22 23 24 25 26 27 121 328 229 3130
AprilMarch
1000
vehicles/h
0
2000 B
0
80103
40103
N3,cm-3
SCO
0
60
30
2000
0
1000
C
g/m3
PM2.5
PM2.5-10
PM10
PM1
1000
0
2000 A
0
10
5
BC,g/m3
Fig. 8. Hourly mean values of road traffic intensity at the coastal Anaga Avenue (vehicles h1) and of the particle BC, N3 and PMx concentrations at the SCO site
from March 21st to April 3rd 2006.
BC
6
12
6
12
0-5h
7-9h
11-17hcentral
daylight
night
morning
N PM2.5 PM2.5-10
10
20
PM1
10
20
20
40
10
20
20
40
20
40
10
20
10
20
10
20
6
12
N3 x103
35
70
35
70
35
70B2
B3
B1
D2
D3
D1
C2
C3
C1
E2
E3
E1
A2
A3
A1
Fig. 9. Hourly mean concentrations of the particle BC, N3 and PMx for each wind direction at several times of the day at the SCO site.
S. Rodrguez et al. / Atmospheric Environment 42 (2008) 652365346532
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11/12
induced nucleation may significantly contribute to the urban
ultrafine particle concentration.
The results of this study show how the strong changes in
daylight to night meteorological conditions (which in-
cludes inland entries of clean air during daylight) exert
a great/major influence on the complex relationship be-
tween the number concentration and other aerosol con-
centration metrics. This, and other processes, not yet well
characterised, may contribute to the large spatial variability
in the particle number concentration as described by Hoek
et al. (2008).
According to Kulmala et al. (2004), new particle forma-
tion rates in a coastal environment as high as those in indus-
trial plumes are frequently recorded. This could, in part, be
due tothefactthat someof the factors which may favournu-
cleation are present in the coastal environment: (i) enough
high relative humidity to favour binary H2OH2SO4 nucle-
ation (Easter and Peter, 1994; Olivares et al., 2007), (ii) rela-
tively clean air conditions (low aerosol surface area
concentration) due to the marine air entries) and (iii) the
mixingof twoair parcels with differenttemperature anddif-
ferent relative humidities (Nilsson and Kulmala, 1998).
Acknowledgements
This study was financed by the Ministry for the Environ-
ment of Spain (Direccion General de Calidad Ambiental;
Project B026/2007/3-10.1: Evaluacion integral del impacto
de las emisiones de partculas de los automoviles en la cal-
idad del aire urbano). The Council of Santa Cruz de Tener-
ife and the Departments of Environmental Health and of
the Environment of the Canary Islands Government also
contributed to this study. Measurements at SCO are per-
formed within the framework of the GURME (GAW) pro-gram. Part of this study was performed into the
framework of the project- GRACCIE (CONSOLIDER
INGENIO; Ministry of Education and Culture of Spain).
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50
0
100
20 400
C PM10
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40
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A PM2.5
g/m3
PMx SCO, g/m3
25
0
50
DPM2.5-10
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r2= 0.54
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TC vs. SCOGL vs. SCO GL vs. SCO
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100GL vs. SCO
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y=1.2x + 17.7
r2= 0.89
y=0.9x + 20.7
r2= 0.82
y=1.0x + 1.0
r2= 0.88
Fig. 10. Daily mean concentrations of PM2.5, PM2.510 and PM10 at city centre sites (GL and TC) versus at SCO coastal urban background.
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