Ri. Smith et al., Regional estimation of pollutant gas dry deposition in the UK: model description, sensitivity analyses and outputs, ATMOS ENVIR, 34(22), 2000, pp. 3757-3777
A "big-leaf" resistance analogy model for dry deposition of sulphur dioxide
, nitrogen dioxide, ammonia and nitric acid is described with a stomatal co
mpensation point included to allow bi-directional exchange of ammonia. The
model derivation is constrained by measurement data and it is parameterized
for UK conditions. Monthly average dry deposition estimates are provided a
t the 5 km x 5 km spatial scale. The model uses data available nationally a
t the appropriate spatial and temporal scales, such as gas concentration, l
and use, wind speed, temperature, rainfall and vapour pressure. A method is
presented to overcome the lack of suitable solar radiation data. The effec
t of uncertainty in model inputs and in model parameterization is explored
using sensitivity analyses. SO2 deposition is sensitive to variation in gas
concentration, wind speed and wet surface uptake parameters. NO2 depositio
n is sensitive to parameters and inputs regulating stomatal behaviour, incl
uding solar radiation and temperature, as well as to gas concentration. The
use of monthly or annual average NO2 concentrations may underestimate depo
sition substantially in some areas. HNO3 dry deposition is sensitive to win
d speed and concentration. NH3 dry deposition to moorland and forest land u
ses, where the majority of deposition occurs, is sensitive to concentration
, wind speed and choice of canopy resistance parameters. For arable and gra
ssland areas, with both deposition and emission of NH3, the model is sensit
ive to all the model inputs and parameter choices. A full uncertainty analy
sis requires further work on the reliability of input variables and model p
arameter choices but these results quantitatively focus on the important ar
eas of the model for each gas. Estimated dry deposition to the UK (excludin
g Northern Ireland) of SO2 is 135 GE S yr (-1) for 1996, for NH3 is 97 Gg N
yr(-1), for NO2 is 26 Gg N yr(-1) and the preliminary estimate for HNO3 is
42 Gg N yr(-1). For sulphur and reduced nitrogen, estimated dry deposition
accounts for 40% of total deposition, including wet and cloud droplet depo
sition. NO2 dry deposition only accounts for 15% of total oxidised nitrogen
deposition, but another 25% may come from the dry deposition of HNO3, givi
ng a similar 40% overall by dry deposition. The sensitivity of the model to
parameter values and the comparisons of modelled output with measurements
show that parameter choices may be valid only at the scale of European coun
tries rather than the whole continent. (C) 2000 Elsevier Science Ltd. All r
ights reserved.