成都市冬季相对湿度对颗粒物浓度和大气能见度的影响

Effect of Relative Humidity on Particulate Matter Concentration and Visibility During Winter in Chengdu

利用成都市城区2015年12月的连续在线观测数据,如相对湿度(RH)、能见度、颗粒物(PM_(10)、PM_(2.5)和PM1)浓度、气态污染物(SO_2和NO_2)浓度以及PM_(2.5)中SO_4^(2-)和NO_3^-浓度,探讨RH对颗粒物浓度和大气能见度的影响.结果表明,高颗粒物浓度和高RH协同作用导致低能见度事件.观测阶段,PM_(2.5)在PM_(10)中的平均比重为64%,表明成都市冬季细颗粒物污染严重;随着RH增加,PM_(2.5)/PM_(10)显著增加,表明高RH会加重细颗粒物污染.随着PM_(2.5)浓度增加,能见度呈幂指数下降;在相同PM_(2.5)浓度下,RH越高,能见度越低.当颗粒物浓度较低时,RH对能见度的影响作用较强;当颗粒物浓度较高时,大气消光主要由PM_(2.5)浓度控制,RH对能见度的影响减弱.当RH大于70%时,硫氧化率(SOR)和氮氧化率(NOR)的均值分别从0.27和0.11(RH小于40%)增长至0.40和0.19,表明较高RH对二次硫酸盐和硝酸盐的生成有显著的促进作用,二次硫酸盐和硝酸盐单独或协同影响空气质量.

The effect of relative humidity（ RH） on particulate matter concentrations and atmosphere visibility were investigated using the continuous on-line observed data of Chengdu city during December 2015,including RH,visibility,the concentrations of particulate matters（ PM10,PM2.5 and PM1） and gaseous pollutants（ SO2 and NO2）,and the concentrations of SO4^2- and NO3^- in PM2.5. The results showed that the haze process occurred because of the synergistic effects of higher particulate matter concentrations and RH,leading to the reduction of visibility. The average ratio of PM2.5 to PM10 was 64% and it significantly increased with the increase of RH during observation period,which indicated that the pollution of fine particles during winter in Chengdu was serious,and high RH aggravated the pollution caused by fine particles. Visibility decreased exponentially with the increase of particulate matter concentrations. When RH was higher,visibility was lower at the same concentrations of particulate matter. RH had a strong effect on visibility at lower particle concentrations,while the effect of RH on the visibility decreased,and atmospheric extinction was controlled by PM2.5 concentrations at higher particle concentrations. With RH increasing from less than 40% to more than 70%,the average sulfur oxidation ratio（ SOR） and nitrogen oxidation ratio（ NOR） increased from 0. 27 and 0. 11 to 0. 40 and 0. 19,respectively,indicating that higher RH significantly promoted the formation of secondary sulfate and nitrate. Secondary sulfate and nitrate separately or coordinatively influenced the air quality.