Sensitivity of photolysis rates and ozone production in the troposphere to aerosol properties

Abstract

Aerosol impacts on NO2 photolysis rates and ozone production in the troposphere are studied by applying a modern sensitivity analysis technique “ADIFOR” on a coupled transport/chemistry/radiative transfer model. Four representative types of tropospheric aerosol (rural, urban, maritime, and desert) are evaluated in terms of loading strength and radiative characteristics. The effects of relative humidity (RH), aerosol vertical loading profile, and NOx (NO + NO2) emission are also studied. The presence of absorbing aerosols in the boundary layer is found to inhibit near‐ground ozone formation and to reduce ground level ozone by up to 70% in polluted environments. The presence of strongly scattering aerosols may increase ozone concentration in the lower boundary layer, but their effects vary with season, NOx, nonmethane hydrocarbon emission (NMHC), and temperature. Ozone production in the upper troposphere can be either enhanced or weakened, depending on the scattering and absorbing ability of aerosol particles and availability of NOx. In the lower troposphere, NO2 photolysis and ozone production rates are most sensitive to urban aerosol, followed by rural, then desert, and finally, maritime aerosol. As expected, NMHC, and NOx emissions also are found to have a large influence on O3 formation.