天津市夏季灰霾与非灰霾天气下颗粒物污染特征与来源解析

年6—8月在天津市区进行的连续灰霾观测发现,灰霾发生的天数占观测时段的1/3. 灰霾日与非灰霾日颗粒物质量浓度存在显著差异,灰霾日ρ(PM_2.5)与ρ(PM₁₀)的平均值分别是非灰霾日的1.64和1.55倍. 灰霾日S含量高于非灰霾日近50%；灰霾日ρ(SO₄2-)和ρ(NO₃-)明显高于非灰霾日,其中灰霾日ρ(NO₃-)增幅最高可达251.02%；灰霾日PM_2.5和PM₁₀中的ρ(OC)、ρ(EC)均是非灰霾日的1.25倍以上. 灰霾日与非灰霾日的气象条件相近,表明此次观测期间天津市区夏季灰霾天气发生与气象条件的关系不大. 使用CMB模型(化学质量平衡模型)对PM_2.5来源进行的解析表明,二次硝酸盐和二次硫酸盐对灰霾日ρ(PM_2.5)的贡献率分别是非灰霾日的2.17和1.34倍,而其他源类在灰霾日和非灰霾日的贡献差异不明显,说明二次离子可能是造成天津市区夏季灰霾最主要的颗粒物源类. 

Characteristics and Sources of Particulate Matter during Hazy and Non-Hazy Episodes in Tianjin City in Summer

Continuous observation of haze episodes in downtown Tianjin was conducted from June to August in 2011. The results showed that one-third of the period were hazy days. There was a significant difference in the mass concentrations of the particles during the hazy and non-hazy days. PM2.5 and PM₁₀ concentrations on the hazy days were 1.64 and 1.55 times higher than those on non-hazy days. When the haze occurred, the elemental percentage of S was about 1.5 times higher than that during the normal days. ρ(SO₄2-) and ρ(NO₃-) in the hazy days were clearly higher than those in the non-hazy days, and the largest increase of ρ(NO₃-) during the hazy days was up to 251.02%. Both OC and EC in PM2.5 and PM₁₀ during the hazy days were 1.25 times more than those in the non-hazy days. Similar weather conditions in the hazy and non-hazy days suggested that the weather conditions did not play a great role in the occurrence of haze during the observation period. Analysis of the sources of PM2.5 by the chemical mass balance (CMB) receptor model showed that contributions of the secondary nitrate and sulfate on the hazy days were 2.17 and 1.34 times higher than on the non-hazy days, while the contributions of the other sources were not significant. These results demonstrated that secondary particles may be the primary source of summer haze.