Abstract
Tianjin, a city located in North China, is heavily polluted with frequent haze, particularly in winter. In this study, continuous online field observations of the sulfate, nitrate, ammonium, PM2.5, and gaseous pollutant concentrations in addition to the meteorological parameters were conducted in Tianjin during the 2014–2015 winter (December–January–February). The PM2.5 concentrations ranged from 5.6 to 495.6 µg m–3, with an average value of 112.2 ± 96.1 µg m–3. The worst pollution was observed in January, when levels on 10% of the days exceeded 250 µg m–3, qualifying as severely polluted, and four haze episodes, each lasting 5–7 days, occurred in rapid succession (separated by ~1-day intervals). Back-trajectory and chemical composition analysis suggested that elevated levels of secondary ionic aerosol species were a primary cause of these episodes. Regional transport of PM2.5 also played a large role in the formation of haze. CO was selected as an inactive chemical tracer in studying the chemical process of PM2.5 formation. The results indicated that when high concentrations of PM2.5 were present, the formation of secondary PM2.5 increased while the photochemical production of O3 ceased. The sulfur oxidation ratio [SOR = nSO42–/(nSO42– + nSO2); n refers to the molar concentration] and nitrate oxidation ratio [NOR = nNO3–/(nNO3– + nNO2)] increased with the PM2.5 level, and heterogeneous processes on the surfaces of fine particles rather than photochemistry drove the haze events. This research elucidates haze formation mechanisms, which must be understood in order to create effective control policies in Tianjin.
Highlights
Epidemiological studies have reported that exposure to air pollution, especially fine particulate matter (PM2.5), adversely affects human health, including contributing to respiratory and cardiovascular diseases (Peng et al, 2009; Li et al, 2017b)
The results indicated that when high concentrations of PM2.5 were present, the formation of secondary PM2.5 increased while the photochemical production of O3 ceased
A haze episode was observed during the Chinese Spring Festival (January 31–February 7) when large amounts of fireworks were set off, increasing regional PM2.5 pollution levels (Kong et al, 2015)
Summary
Epidemiological studies have reported that exposure to air pollution, especially fine particulate matter (PM2.5), adversely affects human health, including contributing to respiratory and cardiovascular diseases (Peng et al, 2009; Li et al, 2017b). Environmental pollution by PM2.5 has become a serious problem in China, in economically developed regions, such as the Yangtze River Delta region (Shen et al, 2016; Zhang et al, 2016), Pearl River Delta (Tan et al, 2016a; Tan et al, 2016b), and the BeijingTianjin-Hebei region (Ma et al, 2017; Zhang et al, 2018). The city of Tianjin, located in the southeast area of the Beijing-Tianjin-Hebei region, faces severe PM2.5 pollution (Tian et al, 2016; Wang et al, 2016; Zhou et al, 2016a). The current understanding of the sources and formation mechanisms of such pollution haze events is limited. Assessing the PM2.5 pollution in Tianjin is an urgent requirement
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
