广州城区近地面层大气污染物垂直分布特征

为更好地了解广州城区近地面层大气污染物的扩散与输送过程,利用广州塔4层大气污染物垂直梯度观测平台(高度分别为地面、118、168和488 m)于2014年1月—2015年12月对多种大气污染物进行连续观测,分析了广州城区近地面层大气污染物的垂直分布特征.结果表明:①ρ(PM₁₀)、ρ(PM_2.5)、ρ(PM₁)、ρ(NO₂)和ρ(NO)随高度的上升而降低,其中ρ(PM₁₀)、ρ(PM_2.5)和ρ(PM₁)在低层(地面点位)—高层(488 m点位)的递减率分别为35%、30%和26%,ρ(NO₂)和ρ(NO)分别为75%和84%；ρ(O₃)随高度上升而增加,其低层—高层的增长率为135%；ρ(SO₂)和ρ(CO)则随高度上升先增后减.②除ρ(O₃)外,其余污染物浓度均符合“冬强夏弱”的季节特征,ρ(O₃)则在夏秋季较高,春冬季较低.冬季ρ(PM₁₀)、ρ(PM_2.5)、ρ(NO₂)和ρ(NO)高、低层间差异为全年各季最大,分别为38.6、18.5、49.4和31.9 μg/m3.③各污染物小时浓度日变化特征均不同程度地受混合层发展过程的影响,各高度污染物浓度在一天中混合层高度最高的时段(12:00—17:00)最接近,而在其余时段分层较明显.除O₃外,其余污染物质量浓度在中、低层大致呈早晚双峰分布,而在高层大致呈单峰分布.ρ(O₃)则在各层均保持单峰分布,峰值一致出现在14:00.④对一次典型污染过程分析发现,不同高度的ρ(PM_2.5)和ρ(NO₂)最大差值分别可达183.0和148.0 μg/m3,ρ(PM_2.5)显著地受到本地近地面污染源的影响,污染物高浓度区域主要集中在488 m以下. 

Vertical Distribution Characteristics of Air Pollutants in the Near-Surface Atmospheric Layer in Guangzhou Urban District

To further understand diffusion and transport of air pollutants in the near-surface atmospheric layer in Guangzhou urban district, measurements of particulate matter (PM₁₀, PM_2.5 and PM₁) and pollution gases (SO₂, CO, O₃, NO and NO₂) were conducted on the Canton Tower at the height of ground level, 118 m, 168 m and 488 m respectively from January 2014 to December 2015. Vertical distribution characteristics of several air pollutants were analyzed and discussed. The results showed that:1) the concentrations of PM₁₀, PM_2.5, PM₁, NO₂ and NO basically decreased with height, with decreasing rates of 35%, 30%, 26%, 75% and 84%, respectively, from the bottom layer (ground site) to the top layer (488 m site). O₃ showed an opposite tendency with an increasing rate of 135%. The concentrations of SO₂ and CO increased first and decreased afterwards with height. 2) All pollutants except O₃ showed high concentrations in winter and low concentrations in summer, while O₃ showed higher concentrations in summer and autumn than in winter and spring. The concentrations of PM₁₀, PM_2.5, NO₂ and NO showed the largest differences between top layer and bottom layer in winter, with the values of 38.6,8.5,9.4 and 31.9 μg/m3, respectively. 3) Diurnal variations of atmospheric pollutants were influenced by the evolution of the mixing layer. Concentrations of pollutants showed smallest differences between layers from 12:00-17:00, when the height of the mixing layer reached the highest during the whole day, and showed greater differences at the other periods. All pollutants except O₃ roughly showed double peaks in the morning and at night at the middle and the ground layers, while roughly showing a single peak at the top layer. O₃ reached its highest concentration at 14:00 and kept its single peak distribution curve at all layers. 4) Analysis of a typical air pollution episode showed that the greatest differences between each height were 183.0 μg/m3 for PM_2.5 and 148.0 μg/m3 for NO₂. The concentration of PM_2.5 was obviously affected by local near-surface emission sources, and regions of high pollutant concentrations were mostly below 488 m.