Investigating the large source of particulate mass from nitrophenols observed in Beijing during winter haze events

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Exposure to poor air quality is the top environmental risk factor of premature mortality globally with an estimated 4 million premature deaths in 2015 from long-term exposure to current levels. By far the most damaging air pollutant to health is particulate matter (PM). The International Agency for Cancer Research has recently classified air pollution as a known carcinogen, with particle pollution being most closely associated with increased cancer rates. Chinese megacities, such as Beijing and Guangzhou, frequently exceed recommended exposure guidelines for particles less than 2.5 microns in diameter (PM2.5). According to official data, the annual mean concentrations of PM2.5 in 2016 in Beijing and Guangzhou were nearly 7 and 4 times higher than World Health Organisation guidelines. A study of 272 Chinese cities found that increases in PM2.5 could be linked to increases in mortality, chronic obstructive pulmonary disease, respiratory diseases, stroke, coronary heart diseases, hypertension and from cardiovascular disease. Therefore the population in Chinese megacities is subjected to damaging levels of particles over extended periods. One of the aims of the recent NERC/MRC funded Air Pollution and Human Health in a Chinese Megacity program was to investigate the sources of PM and develop strategies to reduce exposure to harmful levels of air pollution. Aerosol samples collected during two field deployments in Beijing were analyzed and unusually high levels of nitrophenolic compounds were observed. Nitrophenols can have a range of important atmospheric impacts. Nitro-aromatic compounds, and their atmospheric and biological reaction products, have detrimental effects on human and plant health. For instance, toxic effects in humans after dermal, oral, or respiratory exposure include gastrointestinal, neurological and reproductive disorders, cirrhosis of the liver, hepatitis, cataracts, respiratory and skin irritation, nephrotoxicity, and haematological defects. Some nitrophenols are phytotoxic and may be harmful to plants and aquatic life. The amounts of nitrophenols observed in Beijing were much higher than in previous studies in urban areas and the source of these compounds is unclear. This ambitious project will bring together expertise in chemical mechanism development (Rickard), simulation chamber experiments (Wang) and detailed aerosol composition measurements (Hamilton) to understand the sources and formation processes of nitrophenols and secondary organic aerosol from the atmospheric oxidation of aromatics and phenolic species, under conditions observed in the Beijing urban atmosphere. This project will address key uncertainties arising from the measurements of particle composition during haze events in Beijing and widen the results by applying the methodologies to a different Chinese megacity, Guangzhou. We will improve current representations of phenolic chemistry in the Master Chemical Mechanism (MCM), which is extensively used in a wide variety of air quality science and policy applications. This will be used to design simulation experiments at the Guangzhou Institute of Geochemistry to study the formation of nitrophenols under controlled conditions. We will measure the atmospheric levels of nitrophenols in Guangzhou in summer and winter and combine this with additional data from Beijing to determine the sources and factors that control nitrophenol concentrations.We will also initiate collaboration between the Chinese partner institute and the EUROCHAMP-2020 network, which aims to integrate the most advanced European atmospheric simulation chambers into a world-class infrastructure for research and innovation. Long lasting impact will be achieved through a knowledge exchange placement, where a member of staff from GIG will spend 12 weeks in York to receive training on the MCM and the protocols developed in Europe to model the background chemistry within simulation chambers.