Trends in sunshine duration and atmospheric visibility in the Yunnan-Guizhou Plateau,1961-2005

Using the observed data from 184 stations over the Yunnan-Guizhou Plateau （YGP） from 1961 to 2005, the long-term trends in sunshine duration, cloud amount, dry visibility （Vd）, dry extinction, and water vapor over the YGP are analyzed. The results show that 85% of the stations recorded shortening annual sunshine duration, with the decrease rates between -12.2 and -173.7 h/10yr. Results of Mann-Kendall tests indicate that, among the stations with decreasing sunshine duration, 63.7% of them experienced an abrupt change that started in the 1970s and peaked in the 1980s. This decreasing trend has reversed in the early years of the 21st century. The cloud cover and water vapor content in the mid and lower levels over the YGP had no obvious changes during the study period. The annual averages of Vd declined from 34 km in the 1960s to 27 km at present. The annual mean dry extinction coefficient trended upward, from 0.176 to 0.190, on the YGP from 1980 to 2005. Analyses of cloud cover, water vapor, atmospheric visibility, and dry extinction coefficient revealed that emitted tropospheric aerosols （including air pollutants） resulting from increased energy consumption over the YGP could be a major Factor influencing the reductions of sunshine duration and atmospheric visibility.

Modeling heterogeneous chemical processes on aerosol surface

To explore the possible impact of heterogeneous chemical processes on atmospheric trace components, a coupled box model including gas-phase chemical processes, aerosol thermodynamic equilibrium processes, and heterogeneous chemical processes on the surface of dust, black carbon （BC） and sea salt is set up to simulate the effects of heterogeneous chemistry on the aerosol surface, and analyze the primary factors affecting the heterogeneous processes. Results indicate that heterogeneous chemical processes on the aerosol surface in the atmosphere will affect the concentrations of trace gases such as H2O2, HO2, O3, NO2, NO3, HNO3 and SO2, and aerosols such as SO42-, NO3- and NH4＋. Sensitivity tests suggest that the magnitude of the impact of heterogeneous processes strongly depends on aerosol concentration and the surface uptake coefficients used in the box model. However, the impact of temperature on heterogeneous chemical processes is considerably less. The ＂renoxification＂ of HNO3 will affect the components of the troPosPhere such as nitrogen oxide and ozone.