Abstract
Abstract. Extremely severe haze weather events occurred in many cities in China, especially in the east part of the country, in January 2013. Comprehensive measurements including hourly concentrations of PM2.5 and its major chemical components (water-soluble inorganic ions, organic carbon (OC), and elemental carbon (EC)) and related gas-phase precursors were conducted via an online monitoring system in Suzhou, a medium-sized city in Jiangsu province, just east of Shanghai. PM2.5 (particulate matter with an aerodynamic diameter of 2.5 µm or less) frequently exceeded 150 µg m−3 on hazy days, with the maximum reaching 324 µg m−3 on 14 January 2013. Unfavorable weather conditions (high relative humidity (RH), and low rainfall, wind speed, and atmospheric pressure) were conducive to haze formation. High concentrations of secondary aerosol species (including SO42−, NO3−, NH4+, and SOC) and gaseous precursors were observed during the first two haze events, while elevated primary carbonaceous species emissions were found during the third haze period, pointing to different haze formation mechanisms. Organic matter (OM), (NH4)2SO4, and NH4NO3 were found to be the major contributors to visibility impairment. High concentrations of sulfate and nitrate might be explained by homogeneous gas-phase reactions under low RH conditions and by heterogeneous processes under relatively high RH conditions. Analysis of air mass trajectory clustering and potential source contribution function showed that aerosol pollution in the studied areas was mainly caused by local activities and surrounding sources transported from nearby cities.
Highlights
Haze is defined as visibility lower than 10 km when relative humidity < 80 %
Some of the volatile particulate matter might be lost at 50 ◦C, but comparisons with collocated filters showed that the loss was less than 10–20 % of the gravimetric mass (Chow et al, 2008)
Excluding the five periods accompanied by precipitation, the other five periods were identified as haze events and all of these events occurred in January 2013
Summary
Haze is defined as visibility lower than 10 km when relative humidity < 80 %. Increased air pollution in China in the past several decades has resulted in frequent occurrences of haze events, which has caused great concern to the scientific community as well as the public (Zhang et al, 2012). Haze events have adverse effects on human health, traffic, climate, and other important aspects (Zhang et al, 2015; Charlson et al, 1987; Ramanathan and Vogelmann, 1997; Tegen et al, 2000; Yu et al, 2002; Tie et al, 2009a, b). Fine particles (PM2.5, particulate matter with an aerodynamic diameter of 2.5 μm or less) are largely responsible for haze formation due to their ability for light extinction including scattering and absorbing solar and infrared radiation (Yu et al, 2014). Water-soluble inorganic ions and carbonaceous species often account for major fractions of PM2.5 and are important contributors to visibility impairment (Tan et al, 2009; Pathak et al, 2009), and have been investigated extensively
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