Abstract
The characteristics of pollutants and the boundary-layer structure during two haze events in the summer and autumn of 2014 in Shenyang, Northeast China, were comparatively analyzed by using measurements of the mass concentrations of PM10, PM2.5, O3, NO2, SO2, and CO; vertical profiles of meteorological parameters from a 100-m high tower; and radiosonde data. The results showed that PM concentrations increased rapidly during the two haze events, resulting in visibility that decreased to 1400 and 405 m, respectively. The weak haze event on 16 June was characterized by high O3 but low NO2 mainly due to the photochemical reaction, while all the pollutants increased during the severe haze event on 31 October, which was affected by pollutant emissions and meteorological conditions. The PM2.5 concentration had a good correlation with friction velocity (u*) but did not have an obvious relationship with , which means that the haze events were largely affected by the dynamic effect of turbulence and less so by its thermal effect. According to the radiosonde data, a single inversion layer with an inversion intensity of 1.6°C/100 m existed during the weak haze event, whereas double inversions and even more occurred during the severe haze event, with the inversion intensity larger than 2–4°C/100 m. Such stable atmospheric conditions favored the accumulation of pollutants. Backward trajectory analyses showed that the weak haze event was probably caused by pollutant transport from North China, whereas the severe haze event was generated mostly by local pollutants.
Highlights
Haze is a phenomenon that usually occurs in the nearsurface layer and consists of fine airborne aerosols, including sulfate, nitrate, ammonium, particulate organic matter, and black carbon, as well as other chemical species (Liu et al, 2013)
A severe haze event lasted from 12:00 Local Time (LT) on October to 08:00 LT on 1 November 2014 and reached the upper limit of air quality index (AQI) (= 500) for ambient air quality standards in China on October; it was the most severe haze pollution event in Shenyang in 2014
The characteristics of air pollutants (PM10, PM2.5, SO2, NO2, O3, and CO) and the near-surface layer structure during a weak summer haze event and a severe autumn haze event in 2014 were comparatively analyzed based on the measurements of mass concentrations of pollutants from eleven air-quality monitoring stations and the profiles of wind speed, air temperature, and relative humidity observed from a 100 m-high meteorological tower in Shenyang, an urban city in Northeast China
Summary
Haze is a phenomenon that usually occurs in the nearsurface layer and consists of fine airborne aerosols, including sulfate, nitrate, ammonium, particulate organic matter, and black carbon, as well as other chemical species (Liu et al, 2013). Their results indicated that high concentrations of particles in the residual layer can lead to severe pollution the morning through convective transport of particles to the surface Such studies have rarely been conducted in Northeast China, mainly due to a lack of simultaneous measurements of pollutant concentrations and vertical distributions of meteorological parameters in the nearsurface layer (Wang et al, 2010; Fang et al, 2017). This work comparatively study the characteristics and evolution of air pollutants and the near-surface layer structure during a summer weak haze event and an autumn severe haze event in 2014 in Shenyang, mainly using the air quality monitoring data, the vertical distributions of meteorological parameters obtained from a 100-m tower, and radiosonde data.
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