Abstract
This work reports the day-night differences of a suite of chemical species including elemental carbon (EC), organic carbon (OC), water-soluble organic carbon (WSOC), water-soluble organic nitrogen (WSON), selected polycyclic aromatic hydrocarbons (PAHs), and secondary inorganic ions (NO3−, SO42−, NH4+) in ambient fine particles (PM2.5) collected from 23 July to 23 August 2016 in Changzhou, China. Mass concentrations of PM2.5 and SO42− show a 10–20% increase during daytime, while NO3− concentration decreases by a factor of three from nighttime to daytime due to its semi-volatile nature. PAHs, EC, and WSON show higher mass concentration in the night too. Mass ratios of WSOC to OC are high in both day and night, indicating that secondary organic aerosol (SOA) formation could occur throughout the day, while the slightly higher ratio during daytime suggests a more significant contribution from daytime photochemical oxidation. Strong positive correlations between HULIS-C and WSOC, and HULIS-C with O3 both in day and night, imply that HULIS-C, similar to WSOC, is mainly composed of secondary species. HULIS-C accounted for a large fraction of WSOC, with an average of ~60%. Moreover, the average WSON concentrations are 1.08 and 1.46 µg/m3, constituting ~16% and ~18% of water-soluble total nitrogen in day and night, respectively. Correlation analyses suggest that WSON is also predominantly produced from secondary processes. PAHs concentrations are found to be very low in summer aerosols. Overall, our findings highlight the dominant contribution of secondary processes to the major aerosol components in Changzhou, suggesting proper measures to effectively reduce gaseous precursors are also important to improve air quality.
Highlights
Atmospheric fine aerosols (PM2.5 ), derived from natural and anthropogenic sources, can significantly affect air quality, visibility, human health and the earth’s climate
Daytime photochemical reactions facilitate the oxidation of volatile organic compounds (VOCs) to form secondary organic aerosols (SOA), which increases the water-soluble organic carbon (WSOC) and secondary OC (SOC), as well as the WSOC/OC ratios [11]
This study presents results on OC, elemental carbon (EC), WSOC, Humic-like substances (HULIS)-C, water-soluble organic nitrogen (WSON), polycyclic aromatic hydrocarbons (PAHs), and other major inorganic constituents in Changzhou PM2.5 using samples collected during day and night in summer, respectively
Summary
Atmospheric fine aerosols (PM2.5 ), derived from natural and anthropogenic sources, can significantly affect air quality, visibility, human health and the earth’s climate. As a significant fine aerosol component, OA contributes to the formation and evolution of atmospheric haze [3]. Meteorological conditions and anthropogenic activities in urban areas can vary significantly from day to night [8], especially summer has strong solar radiation during the day, which in turn affects the formation and evolution of atmospheric aerosols. Investigations on day-to-night variation [9,10] are not fully clarified. Investigations on the day-night variation of PM2.5 and its components are valuable to better understand the origin, formation, and chemical transformation of airborne particulate matter
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