Size-resolved aerosol water-soluble ionic compositions in the summer of Beijing: implication of regional secondary formation

Abstract

Abstract. To characterize aerosol pollution in Beijing, size-resolved aerosols were collected by MOUDIs during CAREBEIJING-2006 field campaign at Peking University (urban site) and Yufa (upwind rural site). Fine particle concentrations (PM1.8 by MOUDI) were 99.8±77.4 μg/m3 and 78.2±58.4 μg/m3, with PM1.8/PM10 ratios of 0.64±0.08 and 0.76±0.08 at PKU and Yufa, respectively, and secondary compounds accounted for more than 50% in fine particles. PMF model analysis was used to resolve the particle modes. Three modes were resolved at Yufa, representing condensation, droplet and coarse mode. However, one more droplet mode with bigger size was resolved, which was considered probably from regional transport. Condensation mode accounted for 10%–60% of the total mass at both sites, indicating that the gas-to-particle condensation process was important in summer. The formation of sulfate was mainly attributed to in-cloud or aerosol droplet process (PKU 80%, Yufa 70%) and gas condensation process (PKU 14%, Yufa 22%). According to the thermodynamic instability of NH4NO3, size distributions of nitrate were classified as three categories by RH. The existence of Ca(NO3)2 in droplet mode indicated the reaction of HNO3 with crustal particles was also important in fine particles. A rough estimation was given that 69% of the PM10 and 87% of the PM1.8 in Beijing urban were regional contributions. Sulfate, ammonium and oxalate were formed regionally, with the regional contributions of 90%, 87% and 95% to PM1.8. Nitrate formation was local dominant. In summary regional secondary formation led to aerosol pollution in the summer of Beijing.

Secondary Formation of Sulfate and Nitrate during a Haze Episode in Megacity Beijing, China

“…As illustrated in Fig. 11, the theoretical equilibrium constant Ke' followed the function of temperature in both haze and non-haze episodes, which was in accordance with previous studies (Guo et al, 2010;Ianniello et al, 2011); while nearly a quarter of points in haze episode did not follow the function with sharply smaller Ke'. These points were mainly distributed in RH higher than 66%, where deliquescent particles existed and the NH 4 NO 3 ion strength fraction Y was used in Ke' calculation.…”

“…Both laboratory experiments and in situ observations suggest that the aqueous oxidation of SO 2 is attributed to catalysis by metals, such as iron and manganese (Turšič et al, 2003;Li et al, 2011;Wang et al, 2012). The formation pathway of nitrates, however, is less well known compared to the formation of sulfate, and it is influenced by the emission load of the precursors, the concentrations of oxidants in both the gas and the liquid phase, the characteristics of pre-existing particles and meteorological conditions (Seinfeld and Pandis, 2006;Pathak et al, 2009;Guo et al, 2010;Ye et al, 2011;He et al, 2012). Generally, fine nitrate is more concentrated in homogeneous gas-phase reactions between ammonia and nitric acid in ammoniumrich conditions and is attributed to heterogeneous hydrolysis of N 2 O 5 on the surface of humid and acidic pre-existing particles under ammonium-poor conditions (Seinfeld and Pandis, 2006;Pathak et al, 2009).…”

Comparison of Secondary Organic Aerosol Estimation Methods

“…而且我 国的大气污染日益表现出以强氧化性和高细颗粒物浓 度为特征的区域大气复合污染 [20,21] , 其中高浓度的 SOA 就是大气复合污染的重要表征 [11,14] . 因此有必要对我国 的 SOA 进行深入研究, 并且综合比较不同的估算方法, 探讨这些方法的不确定性以及在我国的适用性.…”

“…敏感性分析是通过 输入 4 种不同的生物质燃烧源谱, 分析源解析结果的稳 定性, 这 4 种源谱包括一种开放式燃烧 [39] 、两种火炉燃 烧 [25,29] 和一种壁炉燃烧 [40] . [6,20] . 北大点 (39°59′21″N, 116°18′25″E) [20,42,43] ; 第二、三、四通道使 用石英膜, 从第二通道的石英膜上切割 1 cm×1.45 cm 的面积用作 ECOC 的分析, 第二通道剩余膜部分和第 三、四通道的石英膜用作颗粒有机物的分析.…”

“…[6,20] . 北大点 (39°59′21″N, 116°18′25″E) [20,42,43] ; 第二、三、四通道使 用石英膜, 从第二通道的石英膜上切割 1 cm×1.45 cm 的面积用作 ECOC 的分析, 第二通道剩余膜部分和第 三、四通道的石英膜用作颗粒有机物的分析.…”