Heterogeneous Uptake and Production from Submicron Aerosols
Atmospheric aerosols (airborne particles) represent the largest uncertainty in estimates of global radiative forcing. They have a direct effect on global climate by reflecting incoming solar radiation, and an indirect effect through the promotion of cloud formation. Compared to gas-phase atmospheric chemistry, relatively little is known about the chemistry of aerosols.
Uptake and Production of HO2
Gas-phase only box models will often over predict concentrations of HO2 in comparison to field measurements. This can, in part be explained by the exclusion of a heterogeneous uptake of HO2 by aerosols.
Heterogeneous uptake is represented by the reaction uptake probability coefficient (probability of reaction given a collision with the aerosol surface). By coupling and aerosol flow tube to a FAGE cell we are able to calculate uptake coefficients for a variety of aerosols and experimental conditions.
Production of Nitrous Acid (HONO)
Daytime concentrations of HONO are currently under-predicted by models indicating an unknown daytime source. In order to investigate what role aerosols may have on the production of HONO, we have set up a flow tube to measure production rates from aerosols under illuminated conditions.
Measurements are made using Photo-Fragmentation Laser Induced Fluorescence (PF-LIF) where the HONO molecule is fragmented into OH and NO, followed by a measurement of the OH fragment using the FAGE technique. This is a fairly new experiment however some production has been observed from TiO2 aerosols.