沙尘表面非均相吸附系数不确定性及其影响的数值模式研究

A Model Study of the Impact of Uncertainty in the Heterogeneous Uptake Coefficients on Dust Aerosol Surface

本文从实验气溶胶样品、实验技术和分析方法三个方面对以往的实验室研究结果进行综合分析,归纳总结出适合东亚地区沙尘气溶胶的非均相吸附系数γ的参考值,并利用区域大气化学模式,模拟研究了非均相吸附系数γ的不确定性对东亚地区沙尘气溶胶非均相化学过程的影响。为了研究非均相反应对γ的敏感性,针对其中四种物质(HNO3、N2O5、O3和SO2)的γ上限值和下限值,分别进行了T-up(上限值)和T-low(下限值)两个敏感实验;针对相对湿度对HNO3和N2O5非均相吸附系数的影响进行了T-rh敏感实验。模拟结果与观测资料进行了对比分析,结果表明模式可以比较好地反映气态物质、气溶胶浓度的演变过程和非均相反应过程。考虑非均相反应后模拟的硫酸盐和硝酸盐浓度与观测值更接近一些。采用γ参考值的模拟结果总体上比采用γ上限值和γ下限值更合理,把γ系数作为相对湿度的函数来处理比作为常数处理更合理。沙尘气溶胶通过非均相化学反应,可以使模拟区域内SO2、NOx和O3的平均浓度下降,使硫酸盐和硝酸盐颗粒物浓度增加,采用γ参考值计算得到3 km以下的上述物质的变化率分别为-3.44%、-5.92%、-1.75%、5.22%和23.25%,显示沙尘表面非均相化学反应对大气化学成分特别是气溶胶有较大的影响;不同γ取值对上述物质变化率有一定影响,其中对硝酸盐和臭氧的影响较大,T-up和T-low模拟结果之间可以相差13.4%和10.1%。

The heterogeneous uptake coefficients（γ） taken from recent laboratory studies are analyzed in terms of aerosol sample,experiment method,and analysis method.The reference γ which are theoretically more suitable for Asian dust aerosol are derived and applied in a regional air quality model to represent heterogeneous reactions of dust aerosol in East Asia.In order to explore the sensitivity of model results to γ values,two sensitivity experiments,namely T-up（upper limit） and T-low（lower limit）,are conducted based on the upper and lower limits of γ values for four gaseous species（HNO3,N2O5,O3,and SO2）.T-rh experiment is also conducted to investigate the influence of relative humidity on γ values for HNO3 and N2O5.Model results using reference γ values are generally better than those using upper and lower limits of γ values in comparison with observations.This study also shows that it would be more reasonable to take γ as a function of relative humidity than to take it as a constant.Through heterogeneous reactions,dust aerosol can make the average concentrations of SO2,NOx,and O3 decrease by 3.44%,5.92%,and 1.75%,respectively,while those of sulfate and nitrate increase by 5.22% and 23.25% below 3 km within the model domain,showing heterogeneous reactions exert more influence on aerosols than gases.The percentages could be changed when using different γ values,especially ozone and nitrate.The model results of ozone and nitrate can differ by 13.4% and 10.1% between T-up and T-low.