沿海城市PM10和PM2.5自动监测过程中质量浓度“倒挂”现象分析与成因探讨

2020年2—3月,位于福建沿海地区中部的莆田市在环境空气质量自动监测过程中出现了严重的PM_(10)和PM_(2.5)质量浓度"倒挂"现象,小时值"倒挂"率为19.86%,日均值"倒挂"率为16.67%。在高相对湿度和低风速气象条件下,颗粒物会出现严重的"倒挂"现象,"倒挂"过程中常伴随着颗粒物和气态污染物(SO_2、NO_2和CO)质量浓度的增加。因此,于2020年2月16日—3月26日开展了颗粒物自动监测和手工监测比对,并结合气象参数、气态污染物质量浓度,以及PM_(10)和PM_(2.5)中水溶性离子和液态水的含量特征,进一步探讨了莆田市颗粒物质量浓度"倒挂"的主要成因。研究表明,PM_(10)和PM_(2.5)自动监测仪器检测原理的差异是导致颗粒物质量浓度"倒挂"的重要原因之一,而气象条件(相对湿度、气温和风速等)、颗粒物质量浓度、颗粒物中主要吸湿组分(NO_3~-、SO_4~(2-)和NH_4~+)和液态水的含量也是颗粒物质量浓度"倒挂"的主要影响因素。莆田市2020年2—3月出现高频率"倒挂"现象是多重因素共同作用的结果,解决该问题需要同时考虑监测仪器检测原理、气象参数、颗粒物质量浓度和吸湿组分等的影响。

The Phenomenon and Formation Causes of Mass Concentration Reversal of PM10 and PM2.5 During Automatic Monitoring in a Coastal City

There was a serious mass concentration reversal of PM₁₀ and PM_2.5 during automatic monitoring from February to March, 2020 in Putian City, located in the central part of the coastal area of Fujian Province. The hourly mass concentration reversal rate of PM₁₀ and PM_2.5 was 19.86% and the daily reversal rate was 16.67%. Under the meteorological conditions of high relative humidity and low wind speed, the mass concentration of PM₁₀ and PM_2.5 appeared to be reversal, which was often accompanied with increased concentrations of particulate matters and gaseous pollutants (SO₂, NO₂ and CO). In order to study the formation causes of mass concentration reversal of PM₁₀ and PM_2.5, comparative study of manual and automatic monitoring of PM₁₀ and PM_2.5, combing with meteorological parameters, the mass concentration of gaseous pollutants, and the characteristics of water soluble ions and liquid water content, were conducted from February 16 to March 26, 2020. The results showed that the differences in monitoring principles between PM₁₀ and PM_2.5 automatic monitors were the main internal factor for the reversal, while the meteorological conditions (relative humidity, temperature and wind speed), the hygroscopic components (NO₃^-, SO₄^2- and NH₄⁺) and liquid water content were the external factors. The high reversal rate of PM₁₀ and PM_2.5 in Putian City from February to March, 2020 was caused by multiple factors, therefore, to solve this problem, the instrument monitoring principle, meteorological conditions, particulate matter concentrations and hygroscopic components, etc. should be taken into considered at the same time.