广州城区夏季大气颗粒物数浓度谱分布特征

于2013年6月2日—7月15日,利用扫描迁移性粒谱仪(SMPS)对广州城区大气17～800 nm的粒子谱进行了连续观测,同时结合在线小时ρ(PM_2.5)及气象数据,对颗粒物污染特征进行了分析. 结果表明:观测期间,凝结核模态粒子、爱根核模态粒子、积聚模态粒子的数浓度范围分别为68～7 687、1 009～47 724、238～14 781 cm-3.平均数浓度谱及体积谱均呈单峰分布,峰值分别出现在50和300 nm左右. 根据双模态对数正态分布模型对平均数浓度谱拟合的结果可知,爱根核模态粒子和积聚核模态粒子的几何平均粒径分别为48和144 nm. 颗粒物数浓度及其谱分布日变化特征明显,在交通高峰及太阳辐射较强的时间段均出现峰值. 在观测阶段,粒子增长现象频繁发生,推测大气光化学反应引起的气-粒转化是广州城区夏季大气颗粒物的重要来源. 7月12—13日广州城区发生了一次典型的大气污染过程,ρ(PM_2.5)由18 μg/m3增至112 μg/m3,能见度降至8 km. 在该时间段,积聚模态粒子体积分数与ρ(PM_2.5)变化一致,R2(相关系数)达到了0.85. 后向轨迹分析表明,污染气团主要来自于西南方向,在陆地停留时间较长. 

Pollution Characteristics of Atmospheric Particle Size and Number Concentrations during Summer in Urban Area of Guangzhou

Atmospheric particles with size range 17-800 nm were measured in urban area of Guangzhou from June 2 to July 15,3. The particulate matter (PM) pollution characteristics were investigated based on the data of number concentrations and size distributions of PM as well as hourly average concentrations of PM_2.5 and meteorological parameters. During the whole sampling period, the number concentrations of nucleation, aitken and accumulation modes ranged from 68 to 7,7, 1,9 to 47,4 and 238 to 14,1 cm-3 respectively. The average number distribution was fitted with two lognormal distributions with geometric mean diameters at 48 nm and 144 nm. The average number and volume distributions exhibited peaks at ~50 nm and ~300 nm respectively. Particle number size distribution showed clear diurnal variation, with peaks related to traffic and strong solar radiation. Particle growth was frequently observed. Secondary photochemical formation contributed greatly to the PM pollution in Guangzhou. A typical pollution episode occurred from July 12 to July 13, during which the concentration of PM_2.5 sharply rose from 18 μg/m3 to 112 μg/m3, and visibility decreased to 8 km. PM_2.5 concentration was strongly correlated with the number concentrations of particles in accumulation mode. Back trajectory analysis showed that air masses originated from the southwest direction and stayed in the continent for a long time during this pollution episode.