Abstract. Quantifying the relative importance of gas uptake on the ground
and aerosol surfaces helps to determine which processes should be included in
atmospheric chemistry models. Gas uptake by aerosols is often characterized
by an effective uptake coefficient (γeff), whereas gas uptake
on the ground is usually described by a deposition velocity (Vd).
For efficient comparison, we introduce an equivalent uptake coefficient
(γeqv) at which the uptake flux of aerosols would equal that
on the ground surface. If γeff is similar to or larger than
γeqv, aerosol uptake is important and should be included in
atmospheric models. In this study, we compare uptake fluxes in the planetary
boundary layer (PBL) for different reactive trace gases (O3,
NO2, SO2, N2O5, HNO3 and H2O2),
aerosol types (mineral dust, soot, organic aerosol and sea salt aerosol),
environments (urban areas, agricultural land, the Amazon forest and water bodies), seasons and mixing heights. For all investigated gases, γeqv ranges from magnitudes of
10−6–10−4 in polluted urban environments to 10−4–10−1
under pristine forest conditions. In urban areas, aerosol uptake is relevant
for all species (γeff≥γeqv) and should be
considered in models. On the contrary, contributions of aerosol uptakes in the Amazon forest are minor compared with the dry deposition. The phase state of
aerosols could be one of the crucial factors influencing the uptake rates.
Current models tend to underestimate the O3 uptake on liquid organic
aerosols which can be important, especially over regions with
γeff≥γeqv. H2O2 uptakes on a variety
of aerosols are yet to be measured under laboratory conditions and evaluated. Given the fact that most models have considered the uptakes of these species on the ground
surface, we suggest also considering the following processes in atmospheric
models: N2O5 uptake by all types of
aerosols, HNO3 and SO2 uptake by mineral dust and sea salt
aerosols, H2O2 uptake by mineral dust, NO2 uptakes by sea
salt aerosols and O3 uptake by liquid organic aerosols.
Results from the DC-8 Inlet Characterization Experiment (DICE): Airborne Versus Surface Sampling of Mineral Dust and Sea Salt Aerosols
