An Observational Study on Physical and Optical Properties of Atmospheric Aerosol in Autumn in Nanjing

Based on observing data of atmospheric aerosol in the north suburban area of Nanjing from September to November in 2007, the number concentration, mass concentration, size distribution and optical properties of atmospheric aerosol particles and the relation to meteorological factors were analyzed, and their concentration and optical properties during hazy and non-hazy days were compared. The results showed that aerosol pollution was serious in autumn in this region; the deterioration of visibility had close correlation to fine particles, that is, the average number concen- tration of aerosol was 17 044.2 cm^-3, in which ultra fine particles accounted for 64.3%; the daily average mass concentration of PM2.5 was 281 μg/m3, and the ratio of PM2.5 to PM10 was 0.74; the accumulation mode particles dominated in number and surface concentration distributions, while the volume concentration distribution presented a main peak at size of 1.0 -2.8 μm; fine particles increased during hazy days compared with non-hazy days; the scatter coefficient closely correlated to the particle size, concentration and atmospheric humidity. It was also indicated that meteorological conditions played a critical role in formation of hazy weather, that is, weak large-scale weather systems, low wind speed, high humidity and strong inversion were favorable conditions for hazy weather in autumn.

Case study of longwave contribution to dust radiative effects over East Asia

In order to evaluate the impacts of LW contribution to aerosol radiative effects over East Asia,a dust longwave radiative parameterization scheme is integrated into the online mesoscale dust forecasting model GRAPES_CUACE/dust.A case modeling study shows that about half at surface and one third at TOA of the dust negative shortwave radiative forcing are cancelled by its positive longwave forcing over the dust affected area.In the dust layer,longwave radiation emitting by dust cools the atmosphere,which counteracts about 17%of shortwave heating of atmosphere during daytime and results in cooling of atmosphere simply during nighttime.At the same time,the atmosphere beyond the dust layer is warmed because of absorbing the LW radiation emitted by dust layer.Dust longwave contribution exerts more evident impact on the air temperature in lower atmosphere and surface.The surface air temperature cooling rate resulting from the dust solar radiation is cancelled about 40%by dust longwave warming at daytime.At nighttime,dust longwave contribution warms land and sea surface.The online calculation of dust LW radiation reduces about 15%relative errors of predicted AOD based on the dust model with only SW radiative feedback.This case study result suggests that dust longwave contribution has important impacts on the earth-atmosphere energy process,especially on the surface and in the lower atmosphere and should not be neglected in the study of dust radiation effects.