基于高分辨质谱在线观测的2011深圳大运会前后PM_1化学组成与粒径分布

On-line measurement of PM_1 chemical composition and size distribution using a high-resolution aerosol mass spectrometer during 2011 Shenzhen Universiade

本文利用先进的高分辨飞行时间气溶胶质谱仪（HR-ToF-AMS）于2011年深圳世界大学生运动会前后（2011年8月3日~9月22日）对深圳市区大气亚微米细粒子（PM1）化学成分和粒径分布进行了在线测量.结果表明,整个观测期间PM1质量浓度平均为51.1±32.6gm3,其中有机物占颗粒物总质量的37.9%,硫酸盐为37.1%,铵盐11.9%,黑碳6.6%（由一台单颗粒黑碳光度计（SP2）单独测量）,硝酸盐5.8%,氯化物0.6%.观测期间各成分（除黑碳外）的粒径分布峰值位于真空动力学粒径550nm附近,而有机物在较小粒径范围（100~200nm）仍有较多质量分布,显示出本地一次源的明显贡献.基于高分辨有机质谱计算得到的有机气溶胶的平均元素组成为：碳34.0%、氢53.2%、氧12.0%和氮0.8%（原子个数百分比）,对应的OM/OC（有机物与有机碳质量比）平均值为1.66±0.16.采用正矩阵因子解析（PMF）模型对有机气溶胶高分辨质谱进行因子解析,得到三类有机气溶胶：HOA（还原态有机气溶胶）,SV-OOA（半挥发氧化态有机气溶胶）和LV-OOA（低挥发氧化态有机气溶胶）,分别占有机物总量的31.3%,39.8%和28.9%,说明二次有机气溶胶（以SV-OOA和LV-OOA之和代表）是有机气溶胶的主体部分.结合气团来源分析不同时段PM1化学组成和粒径分布特征表明,大运会召开期间PM1质量浓度水平比整个观测期间的平均值低60.7%,是气团来自洋面等有利气象条件和黄标车限行等污染源控制措施的综合作用结果.

On-line measurement of the chemical composition and size distribution of submicron aerosol particles （PM0 was conducted in urban Shenzhen, China, using a state-of-the-art high-resolution time-of-flight aerosol mass spectrometer （HR-ToF-AMS） during the 2011 Shenzhen Universiade （August 3-September 22, 2011）. The mean PM1 mass concentration measured was 51.1±32.6 μg m-3 during the campaign, with organic aerosol （OA） accounting for 37.9% of the total mass, followed by sulfate （37.1%）, ammonium （11.9%）, black carbon （6.6%, measured by a single particle soot photometer, SP2）, nitrate （5.8%） and chloride （0.6%）. The average size distributions of the species （except black carbon） all had a peak at -550 nm in vacuum aerodynamic diameter. The size distribution pattern of OA was broader at smaller sizes （100-200 nm）, indicating an obvious contribution from local primary sources. Calculations based on high-resolution organic mass spectrum showed that, C, H, O, and N on average contributed 34.0, 53.2, 12.0, and 0.8% to the total atomic numbers of OA, respectively, which corresponded to an OM/OC ratio （the ratio of organic mass over organic carbon mass） of 1.66±0.16. Three components of OA were identified by positive matrix factorization （PMF） analysis on the high-resolution organic mass spectral dataset, including a hydrocarbon-like （HOA）, a semi-volatile oxygenated （SV-OOA） and a low-volatility oxygenated （LV-OOA） organic aerosol, which on average accounted for 31.3, 39.8, and 28.9% of the total organic mass, respectively. This indicated that OA was dominated by secondary organic aerosol （represented by the sum of SV-OOA and LV-OOA）. Analysis on the PM1 chemical compositions and size distributions in different episodes according to air mass sources showed that, the mean PM1 mass concentration during the Universiade game days was 60.7% lower than that during the whole observation period. This was a combined result of a favorable meteorological condition with air masses coming from the sea and the emission control measures like the restriction of high-emission old vehicles.