“The mass balance IHF method equates the vertical flux of NH 3 from a treated area of limited...
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Transcript of “The mass balance IHF method equates the vertical flux of NH 3 from a treated area of limited...
Mass balance integrated horizontal flux method for quantifying NH3(g) loss
“The mass balance IHF method equates the vertical flux of NH3 from a treated area of limited upwind extent with the net integrated horizontal flux at a known downwind distance (Wilson et al., 1983). “
Hypothetical field situation
wind
-unfertilized area
masts with ammonia traps& anemometers
x x
+ urea
“Try to imagine we have applied urea to a small area (green shaded) inside a larger unfertilized field. Assume the wind is blowing from right to left”.
“Try to imagine we have applied urea to a small area (green shaded) inside a larger unfertilized field. Assume the wind is blowing from right to left”.
NH3(g)
wind direction
urea prills
diffusion & turbulence
convection
NH3(g) NH3(g)
downwind upwind
Zp, height of gas profile development
NH(3) traps
anemometer
x x
“The following diagram is modified from Ryden et al. (1984) and illustrates ammonia production from the soil surface (treated with urea). Ammonia moves upward as a
result of diffusion and turbulence, and moves laterally due to convection. Masts with NH3 traps and anemometers to measure wind speed are placed at upwind and
downwind boundaries”
NH3 conc., µg N m-3
Hei
ght,
m
Zp
c1
downwind
NH3 conc., µg N m-3
Hei
ght,
m
c1
upwind
Wind speed, m sec-1
Hei
ght,
mc1
“These figures illustrate typically profiles of ammonia concentration in the air at downwind and upwind positions, and wind speed. Source: Ryden et al.,1984”.
Horizontal NH3(g)flux calculation
c = concentration, μg/m3
u = wind speed, m/sec
”Horizontal flux, or the product of wind speed x concentration, is calculated for each of the five planes (i)”
i=5
i=3
i=2
i=1
i=4
Vertical NH3(g) flux calculation (Fv)
fetch distance, m
“To calculate Fv a plot of height vs. horizontal flux is made at each of the five planes. The horizontal flux is then integrated over the height intervals and divided by the fetch distance”.
Horizontal flux
Heig
ht
x
x
x
x
x
“Fetch is the distance between downwind and upwind boundaries”.
Fetch distance
NH3(g)
wind direction
urea prills
NH3(g) NH3(g)
downwind upwind
x x
Vertical NH3(g)flux correction for background emissions
Horizontal flux
Hei
ght
x
x
x
x
x
x
x
x
x
x
Horizontal fluxH
eigh
t
downwind mast upwind mast
“To compute the net vertical flux, ammonia flux at the upwind mast position is subtracted from the downwind mast position”.
developed in Australia by Leuning et. al (1985)
eliminates the need for wind speed measurements with anemometers
horizontal flux (NH3 concentration x wind speed) is calculated from the equation!
M = mass of ammonia (µg) collected T = time A = effective cross-section sampling area the shuttle
Passive samplers or shuttles
‘Effective sampling area’ was defined in wind tunnel tests with shuttles
Wind speed (m s-1)
Flow
rate
(10-5
m3 s-1
)
2 4 6 1080
25
20
15
10
5
0
Slope = 2.42 x 10-5 m2
A = effective sampling area
Source: Leuning et al. (1985)Atmospheric Environ.
Mast and shuttles
Shuttles rotate on a pivot and point into wind0.25 m
0.50 m
1.00 m
1.50 m
2.75 m
“Five shuttles are placed on all masts in a gradient spacing with the top shuttle being situated at the approximate Zp height”.
Circular plots (40 m dia.)
+ urea (90 lbs N/a)
background
200 m
urea + Agrotain• known fetch distance (radius = 20 m)• large unfertilized buffer areas
necessary around plots
IHF method requires
Ammonia loss calculationammonia trapped in shuttles is eluted in the lab and elutants run on a Timberline ammonia analyzer
calculations of ammonia are done in Excel spreadsheets
(μg N m-2 sec-1) x time period
losses expressed as a fraction of urea-N applied
M/AT
Hei
ght 4
3
2
5
1
Summary – hopefully more clear
“The mass balance IHF method equates the vertical flux of NH3 from a treated area of limited upwind extent with the net integrated horizontal flux at a known downwind distance (Wilson et al., 1983). “
Key pointsminimal disturbance to site and provides time-
integrated measurement; widely recognized