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

Lead Research Organisation: University of York
Department Name: Chemistry


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.

Planned Impact

Chinese mega cities frequently exceed recommended exposure guidelines for particles less than 2.5 microns in diameter (PM2.5). This project will address a key uncertainty arising from the measurement of organic material in Beijing's particulate matter during winter haze events. Much greater levels of nitrophenols were observed than in most previous studies in urban locations. These compounds may have significant effects on humans, due to their potential cancer risk from exposure, and are harmful to plant life. However, the source of this material in Beijing is unclear; the two most likely sources are from reaction of local traffic emissions or regional biomass burning emissions. This project aims to determine the main source of nitrophenols in Beijing and extend this to a second Chinese megacity, Guangzhou. Guangzhou is the largest city in the Pearl River Delta (PRD) conurbation in south China. In 2015 it had an estimated population of over 13 million inhabitants. The PRD is the most populous metropolitan area in China, with over 40 million inhabitants.

There will be a wide range of beneficiaries of this research. Policy makers in the Chinese Department of Environmental Protection and the municipal/provincial Bureaus of Environment Protection are responsible for improving air quality in China. The will benefit from this research in a number of ways. Improvements to the description of aromatic and phenolic compounds in the Master Chemical Mechanism (MCM) will allow more accurate modelling of ozone and secondary processes such as particle formation. This is particularly important for China, where poor transport fuel quality leads to very high levels of aromatic compounds to the atmosphere. We will also impact policy makers through the connections of Prof Wang (coI) at the Guangzhou Institute of Geochemistry. Prof Wang is a member of the Advisory Committee on Air Pollution Control of Guandong Province, a member of the Consulting Board on Environment and Resources Trials of the High Court of Guangdong Province. He is also a member of Advisory Committee on Environmental Protection in many cities in the Pearl River Delta region. He will feed the results of this project to these groups to ensure maximum impact from the research. Improvements in air quality can lead to large economic benefits through improved health of the population and thus greater productivity and lower health care costs. Businesses will benefit, particularly those that are directly or indirectly affected by air pollution control measures. The general public in China have a strong interest in air pollution, particularly particulate matter. Improvements in air quality will directly benefit them through improvements in health outcomes and reduced disease rates.

By transferring knowledge to the Chinese partner institute, we will also achieve impact that long outlasts the project and aligns with ODA activities. Europe hosts some of the most advanced atmospheric simulation chambers in the World and the EUROCHAMP2020 projects aims to create a world leading infrastructure of partner institutes across Europe. This project will provide a link between EUROCHAMP2020 and Prof Wangs group, who have built the largest simulation chamber in China. The group will have early access to the procedures and protocols being developed in EUROCHAMP2020. In addition, a 12 week knowledge exchange placement for a staff member of GIG in York, providing training on the MCM and how to produce auxillary chamber mechanisms (that describe the background chemistry in the chamber), will allow accurate modelling of the chemistry within the GIG chamber. This is essential to ensure that the findings from the chamber can be extended to atmospheric conditions.


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Description Due to COVID restrictions and the difficulty of obtaining data from Chinese collaborators (due to lockdown in Jan-May 2020) and analysing filters in York (lab shutdown March - Sept 2020), the focus of the project changed slightly to concentrate on both nitrophenols and organosulfates (OS) and nitroxyorganosulfates (NOS) - a series of molecules that provide important information about anthropogenic-biogenic interactions in cities.

The observations show strong diurnal variations of monoterpene derived OSs and NOSs, which peaked during the night, with concentrations increasing from the early evening, highlighting the role of nitrate radical oxidation chemistry. Isoprene derived OSs/NOSs showed strong seasonal profiles, with summer and winter average concentrations of 181.8 and 69.5 ng m-3, respectively, with exponential increases observed at temperatures above 30 °C. Low-NO formation pathways, more typical of remote forested atmospheres, were dominant in the summer, while high-NO pathways became more important in the winter. Isoprene OS formation was strongly dependent on the availability of particulate sulfate, suggesting an extensive heterogeneous chemistry of oxidized isoprene species. As the earth warms, and net zero policies globally lead to increased urba greening and reduction in anthropogenic emissions, the rolw of biogenic-anthropogenic interactions in fomring pollutant aerosols will increase. This work highlights that both temperature and the degree of NOx pollution, both play important roles in deteremining how much aerosol formas from this source.
Exploitation Route The methodologies developed have been iuncluded in upcoming funded projects. The data has been used extensively by a PhD student and Masters Students. The archive of filters will be a useful resource for future projects.
Sectors Environment