Quantifying the effects of a low-ozone event and shallow stratocumulus clouds on ultraviolet erythemal radiation exposure

Meteorological and dosimetric ultraviolet (UV) erythemal radiation (UVER) measurements were performed in Didcot, England, on 6 and 7 April 2017. Both days were characterized by clear-sky conditions in the morning and the afternoon with development of shallow stratocumulus clouds (SSC) around noon. In addition, a low-ozone event occurred on 7 April characterized by a 34 DU (Dobson Unit) drop in total stratospheric ozone content. Compared to 6 April, the ozone mini-hole caused UVER increases of 2.67 standard erythema dose (SED) for diffuse and 4.32 SED for global radiation characterized by radiation amplification factors (RAF) of 1.62 and 1.52, respectively. The total global UVER dose reductions due to SSC coverage amount to 2.33 SED (6 April) and 2.81 SED (7 April). As innovation the RAF is decomposed into two parts, named cloud ozone factor (COF) and radiation amplification factor based on measured data (RAF_m), to quantify the low-ozone event's effect and the SSC influence in independently modifying the UVER doses. Hereby, the weight of each of these two effects acting during the same low-ozone event is expressed by the new COF. In this case, the COF values range between -0.13 and -0.11 for diffuse UVER and -0.03 to -0.07 for the global UV and UV-B parts. A positive COF value (0.18) results for the global UV-A range.

Cross influences of ozone and sulfate precursor emissions changes on air quality and climate

Tropospheric O(3) and sulfate both contribute to air pollution and climate forcing. There is a growing realization that air quality and climate change issues are strongly connected. To date, the importance of the coupling between O(3) and sulfate has not been fully appreciated, and thus regulations treat each pollutant separately. We show that emissions of O(3) precursors can dramatically affect regional sulfate air quality and climate forcing. At 2030 in an A1B future, increased O(3) precursor emissions enhance surface sulfate over India and China by up to 20% because of increased levels of OH and gas-phase SO(2) oxidation rates and add up to 20% to the direct sulfate forcing for that region relative to the present day. Hence, O(3) precursors impose an indirect forcing via sulfate, which is more than twice the direct O(3) forcing itself (compare -0.61 vs. +0.35 W/m(2)). Regulatory policy should consider both air quality and climate and should address O(3) and sulfate simultaneously because of the strong interaction between these species.