厦门地区气溶胶液态水含量特征及其对硝酸根生成的影响

Characteristics of Aerosol Liquid Water Content in Xiamen and Its Effect on Nitrate Production

环境气溶胶中包含大量吸湿性组分,其可吸收液态水,进而改变气溶胶的尺度及环境、气候效应,因此,需要对气溶胶液态水(ALW)开展研究。厦门地区环境空气中的水汽丰富,ALW在气溶胶中占比较大,但关于其特征和影响因素,目前仍缺乏相关报道。利用ISORROPIAⅡ热动力学平衡模型,对厦门地区PM_(2.5)中主要吸湿性物质的含量和特征,以及气溶胶液态水含量(ALWC)的季节和日变化规律进行了分析,并研究了影响ALWC的主要因素及其影响程度。研究结果显示,厦门地区二次离子对气溶胶吸湿性的贡献最大,冬季浓度最高。春梅雨季ALWC的平均值最高,达到了113.5μg/m^(3)。各季节ALWC占气溶胶总质量浓度的比例为37.1%~86.6%。厦门地区能见度和ALWC呈现负相关,ALWC水平决定了大气能见度整体状况。通过敏感性分析发现:硫酸根浓度对ALWC的影响显著,二者呈线性关系;硝酸根在低浓度的时候与ALWC也呈现线性相关,而当其浓度上升到一定水平后,对ALWC的影响不明显;温度变化对于ALWC几乎没有影响;相对湿度对ALWC的影响呈现指数变化。ALW对硝酸根的生成有明显的促进作用。通过分析硝酸根生成速率和ALWC的比值发现,在单位质量浓度条件下,白天ALW对硝酸根的生成的促进能力比夜间更强。此外,从季节角度,秋季单位浓度ALW对硝酸根的生成的促进能力最强。

Ambient aerosols contain a large number of hygroscopic components,which can absorb liquid water,and then change the size of aerosols and their environmental and climate effects.Therefore,it is necessary to study the aerosol liquid water(ALW)content(ALWC).The ambient air in Xiamen is rich in water vapor,and ALWC accounts for a large proportion in aerosols,and its characteristics and driving factors are lack of relevant reports.In this paper,the content and characteristics of main hygroscopic substances in PM_(2.5),as well as the seasonal and diurnal variations of ALWC in Xiamen were analyzed by using the ISORROPIAⅡthermodynamic equilibrium model.The main factors affecting ALWC and degree of influence were also studied.The contribution of secondary ions to aerosol hygroscopicity was the largest in Xiamen,and its concentration was the highest in winter.The average level of ALWC in Xiamen was the highest in rainy season,reaching 113.5μg/m^(3).The average proportion of ALWC in the total mass concentration of PM_(2.5)was 37.1%-86.6%.There was a negative correlation between visibility and ALWC in Xiamen.The concentration level of ALWC determined the overall situation of atmospheric visibility.Using sensitivity analysis method,it was found that sulfate had a significant effect on ALWC,and their concentration was linear.When nitrate concentration was low,it also had a linear correlation with ALWC,but when its concentration reached a certain level,it had no obvious effect on ALWC.In Xiamen,temperature change had little effect on ALWC,while RH had an exponential effect on ALWC.ALW had a significant promotion effect on the formation of nitrate.The analysis of the ratio of nitrate formation rate and ALWC revealed that the promotion ability of ALW on the formation of nitrate was stronger during the daytime.In addition,the strongest promotion ability of unit concentration of ALW for the formation of nitrate was observed in autumn.