影响大气汞化学过程的敏感因子分析

为了分析汞在大气中的化学行为,在一个化学模式中加入汞的气相、气液平衡和液相反应,模拟大气汞及其化合物的演变规律,并分析了气象因子(云、光解率、温度)和化学因子(气态O3、H2O2、HO2、OH和气态零价汞Hg0(g))的初始体积分数对各形态汞及其化合物浓度和Hg0(g)转化率的影响.模拟结果表明,在中等大气污染条件下,Hg0(g)的每小时平均转化率为2.91%.敏感性试验结果表明,云量、光解率、温度、O3和Hg0(g)的初始体积分数对不同形态汞的影响较为显著.云量的增加、光解率的增加、臭氧初始体积分数的升高,各形态汞的平衡时间缩短,除气态氧化汞和一价汞离子外,其他形态汞的平衡浓度均会降低,Hg0(g)的转化率增加.温度增加将抑制Hg0(g)的转化.Hg0(g)的初始体积分数增加,各形态汞的浓度升高,但其平均转化率没有显著变化.不同因子对汞化学过程的相对作用对区域或全球大气汞的环境模拟具有指导意义.

Sensitivity analysis of factors affecting atmospheric mercury chemistry

To analyze the chemical behavior of atmospheric mercury, the gaseous, aqueous and gas-liquid equilibrium processes associated with mercury chemistry were incorporated into a chemistry box model. This modified box-model was used to simulate the evolution of element mercury (Hg0) and speciated reactive mercury. We performed sensitivity analysis to assess the effects of meteorological factors (e.g., clouds, photolytic rate constants, and temperature) and chemical factors (e.g., the initial volume fraction of gaseous ozone (O3(g)), hydrogen peroxide (H2O2(g)), hydroperoxyl radical (HO2(g)), hydroxyl radical (OH(g)) and gaseous elemental mercury (Hg0(g)) on Hg0 and speciated reactive mercury, as well as the average conversion rate of Hg0(g). The average conversion rate of Hg0(g) was 2.91% per hour under conditions of moderate air pollution (base case). The results of sensitivity analysis indicate that cloudiness, photolysis rate, temperature, initial volume fraction of O3(g) and Hg0(g) play important roles in determining concentrations of Hg0 and speciated reactive mercury. The greater the amount of cloud, rate of photolysis or initial concentration of O3(g), the shorter the time that is needed for Hg0 and speciated reactive mercury to reach steady state and low equilibrium concentrations, except for gaseous HgO and Hg+. Under these conditions, the highest average conversion rates of Hg0(g) were found. The conversion of Hg0(g) could be inhibited by increasing temperature. The initial volume fraction of Hg0(g) mainly affects the equilibrium concentrations, with no significant effect on its average conversion rate. This finding can be significant for regional or global simulations of mercury depending on the relative importance of these factors.