Yuanqin Yang

Interdecadal changes of summer aerosol pollution in the Yangtze River Basin of China, the relative influence of meteorological conditions and the relation to climate change

Winter is a season of much concern for aerosol pollution in China, but less concern for pollution in the summertime. There are even less concern and larger uncertainty about interdecadal changes in summer aerosol pollution, relative influence of meteorological conditions, and their links to climate change. Here we try to reveal the relation among interdecadal changes in summers most important circulation system affecting China (East Asian Summer Monsoon-EASM), an index of meteorological conditions (called PLAM, Parameter Linking Air Quality and Meteorological Elements, which is almost linearly related with aerosol pollution), and aerosol optical depth (AOD) in the middle and lower reaches of the Yangtze River (M-LYR) in central eastern China during summertime since the 1960s. During the weak monsoon years, the aerosol pollution load was heavier in the M-LYR and opposite in the strong monsoon years mainly influenced by EASM and associated maintenance position of the anti-Hadley cell around 115°E. The interdecadal changes in meteorological conditions and their associated aerosol pollution in the context of such climate change have experienced four periods since the 1960s, which were a relatively large decreased period from 1961 to 1980, a large rise between 1980 and 1999, a period of slow rise or maintenance from 1999 to 2006, and a relatively rapid rise between 2006 and 2014. Among later three pollution increased periods, about 51%, 25% and 60% of the aerosol pollution change respectively come from the contribution of worsening weather conditions, which are found to be greatly affected by changes in EASM.

Influence of meteorological conditions on explosive increase in O3 concentration in troposphere

Ozone (O3) pollution in the troposphere, especially at the surface layer, has become a focus of attention in recent years. High O3 concentration events tend to occur frequently in north China, Yangtze, the Pearl River Delta, and the Sichuan Basin, among others. Studies on the meteorological contribution to O3 in the troposphere have become a new direction for the scientific community. This research intends to explore how meteorological conditions contribute to O3 pollution in all seasons on the basis of further studies of the PLAM index. Our findings are as follows. (1) In pollution-sensitive areas, following a height uplift in the pollution mixing layer (H_PML), NO2 concentration decreases initially, followed by an explosive increase (EI) in O3 concentration after sunrise. (2) This process varies significantly by season and area. (3) According to an analysis of the meteorological conditions causing rises in O3 concentration within a few hours after sunrise, the initial decrease-subsequent increase in NO2 versus O3 concentration satisfies the law of exponent power rule, according to which seasonal and regional differences in coastal and inland areas depend on coefficients α and β. The explosive increase in O3 concentration, decrease in NO2 concentration, and characteristics of their diurnal cycles are also discussed. (4) Under the meteorological condition of static stability, below the static and stable cover, the H_PML of the polluted mixed layer consistently indicates the reciprocating cycle of day uplift and night pressure. The effect of air pump suction on the pollutant is an important mechanism of large-scale pollution in the study area under the condition of static and stable cover. (5) The influencing mechanism of meteorological conditions in the diurnal H_PML cycle aids in improving the understanding of O3 concentration increases in the troposphere.