上海市秋季典型大气高污染过程中颗粒物的化学组成变化特征

于2010年10月1日至11月30日在上海市城区对大气中颗粒物质量浓度及细粒子化学组分进行了在线连续观测,获得了秋季大气灰霾和沙尘等典型污染过程中颗粒物质量浓度和化学组成的变化特性.观测结果显示,在大气灰霾污染过程中PM₁₀和PM_2.5的日均最高浓度分别达到216~293 μg·m^-3和130~204 μg·m^-3,PM_2.5/PM₁₀的比值在65%以上,总的可溶性无机离子(TWSII)占PM_2.5质量浓度的50%以上,有机碳(OC)和元素碳(EC)的总和占25%~30%.二次可溶性离子(SO₄^2-, NO₃^-, NH₄⁺)占TWSII的83.3%~87.5%,OC/EC的比值在5左右,表明在灰霾污染过程中二次组分对PM_2.5的贡献较大;沙尘天气以粗粒子污染为主,TWSII、OC和EC分别仅占PM_2.5质量浓度的27.2%、13.4%和2.0%,二次可溶性离子(SO₄^2-, NO₃^-, NH₄⁺)占TWSII的55.7%,Ca²⁺、Mg²⁺等地壳组分的比例较灰霾天气明显升高.研究结果还显示,SO₄^2-和NO₃^-等二次离子组分的生成与颗粒物中硫与氮的氧化速率有关,在大气灰霾过程中硫转化率(SOR)和氮转化率(NOR)值较高,分别为0.24±0.10和0.15±0.06,说明SO₂通过二次反应生成SO₄^2-的能力较强,在污染的环境下高浓度的NO₂更有利于向NO₃^-转化.

Chemical characteristics of particulate matters during air pollution episodes in autumn of Shanghai, China

Continuous measurements were conducted in the urban area of Shanghai from October to November,2010.The mass concentrations and chemical characteristics of PM2.5 during different pollution episodes,including haze and sand storm episodes,were obtained.The maximum daily mass concentrations of PM10 and PM2.5 were 216～293 μg·m-3 and 130～204 μg·m-3,respectively.During the haze episode,the ratio of PM2.5 to PM10 was over 65%,the total water soluble inorganic ions(TWSII) accounted for more than 50% of the mass concentration of PM2.5,and the carbonaceous particle(OC and EC) contributed 25%～30% to the PM2.5 mass concentration.Meanwhile,secondary water soluble ions(SO2-4,NO-3,NH+4) contributed 83.3%～87.5% to TWSII,and the ratio of OC/EC was around 5,suggesting the large contribution from secondary formation to PM2.5 during the haze episode.Different from the haze episode,the coarse particle has larger contribution to PM2.5 during the sand storm episode,with TWSII,OC and EC accounting only for 27.2%,13.4%,2.0%,and secondary water soluble ions contributing 55.7% to the TWSII.In addition,larger proportion of crust ions(Ca2+,Mg2+) in PM2.5 was found during the sand storm episode than that during the haze episode.High concentrations of secondary ions in haze days may be resulted from the strong oxidation of sulfur and nitrogen.During the haze episode,the oxidation ratios of sulfur and nitrogen reached 0.24±0.10 and 0.15±0.06,suggesting the strong transformation potentials of NO2 and SO2 to NO-3 and SO2-4.