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”.

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

Heig

ht, m

Zp

c1

downwind

NH3 conc., µg N m-3

Heig

ht, m

c1

upwind

Wind speed, m sec-1

Heig

ht, m

c1

“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

htx

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

Heig

ht

x

x

x

x

x

x

x

x

x

x

Horizontal fluxHe

ight

downwind mast upwind mast

“To compute the net vertical flux, ammonia flux at the upwind mast position is subtracted from the downwind mast position”.

Net vertical NH3(g) calculation

Horizontal flux

Heig

ht

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.

Shuttle design is critical and needs to.…

..mimic the design of Leuning et al. (1985).

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

Continuous measurements

shuttles on mast exchanged weekly with recharged shuttles

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

Heig

ht 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