SO2 noontime-peak phenomenon in the North China Plain
Xu, W. Y.
Zhao, C. S.
Lin, W. L.
Xu, X. B.
A phenomenon of frequent noontime SO<sub>2</sub> concentration peaks was
discovered in a detailed analysis of the SO<sub>2</sub> concentrations in the
North China Plain (NCP). The possible causes and their contributions are
analyzed. The impacts of such a phenomenon on the sulphur cycle were studied
and the implications of the phenomenon for atmospheric chemistry, cloud
physics, and climate were discussed. Different from the more common SO<sub>2</sub>
diurnal patterns with high nighttime concentrations, NCP witnessed high
frequencies of noontime SO<sub>2</sub> peaks, with an occurrence frequency of 50
to 72% at four stations. Down mixing of elevated pollution layers, plume
transport processes, mountain-valley winds, and fog/high RH haze events were
the possible causes. The contribution of each process varies from day to day
and from station to station, however, none of those four processes can be
neglected. SO<sub>2</sub> peaks occurring during noontime instead of nighttime
will lead to a 13 to 35% increase in sulphur dry deposition, a 9 to 23%
increase in gas phase oxidation, and an 8 to 33% increase in aqueous phase
conversions, which will increase the hygroscopicity and the light scattering
of aerosols, thus having important impacts on atmospheric chemistry, cloud
physics, and climate.