EXHALE: EXploiting new understanding of Heterogeneous production of reactive species from AIRPRO: Links to haze and human health Effects

EXHALE will conduct targeted research following on from major findings during the APHH-China phase-1 AIRPRO field campaigns which found that pollutant chemistry is more complex than expected, particularly during the so-called haze events when loadings of particulate matter (PM) were high. Large concentrations of the hydroxyl radical (OH) were observed in both summer and winter, including during haze events, which was unexpected. OH controls the atmospheric lifetime of most trace gases and the formation of secondary pollutants such as ozone and secondary organic aerosols (SOA), and HONO was found to be the dominant OH precursor in Beijing. However, detailed models were unable to fully account for HONO, OH and other radicals, especially during the polluted haze events.

EXHALE will quantify heterogeneous sources of nitrous acid (HONO) and radicals at aerosol surfaces using particulate matter (PM) collected on filters from Beijing ambient aerosol by our Chinese collaborators at Peking University (PKU), including during haze events. The filter samples will be analysed off-line by a variety of analytical methods to determine the composition of the PM, which is known to be highly complex. The filter samples will be sent to Leeds, and the extract from these filters will be used to generate aerosols in the laboratory, and the HONO and radical production rates determined using an illuminated aerosol flow-tube apparatus equipped with a very sensitive detector for HONO, HO2 or RO2 radicals. The production rates will be determined as a function of atmospheric variables and parameterised, and used as input into a box model, constrained to detailed measurements made during the AIRPRO campaigns. The box model will use the detailed Master Chemical Mechanism, and will evaluate the impact of the heterogeneous production processes on radical levels and rates of ozone production, a secondary pollutant harmful to health.

The newly determined production rates will also be used in large-scale regional models, initially for Beijing but then for other Chinese mega-cities, to quantify the impact of heterogeneous production towards regional episodes of ozone and secondary organic aerosol. We will use publically available data from the Chinese air quality monitoring network (>1000 locations), and together with additional data from our Chinese partners, will use regional simulations to scale up implications of these sources, and translate the results across China.

EXHALE consists of a UK-Chinese consortium with complementary expertise and capabilities in both experimental and modelling aspects of atmospheric science. At Leeds there is experimental expertise in the ultra-sensitive measurement of radicals and HONO and aerosol uptake/production of reactive species, and expertise in modelling of gas-phase and aerosol chemical and physical processes on a range of scales using box, regional and global models. At PKU there is expertise in sampling of ambient aerosol and detailed off-line analysis of the composition of Beijing aerosol. The project benefits from collaboration with other Chinese scientists working on urban air pollution in other mega-cities. Towards the end of the EXHALE project, and together with our collaborators at PKU, we will organise a 2-day stakeholder workshop in Beijing to discuss the results from EXHALE and the wider implications for air pollution and its control. In conjunction with our project partners at Shanghai Jiao Tong University we will organise a summer school in 2020 in Shanghai, primarily aimed at PhD students and early career researchers, and to be taught by the EXHALE investigators and our Chinese collaborators and project partners.

Urban air pollution is a severe problem in China, with hazes impacting the lives of ~500 million people. The exposure to pollutant concentrations above World Health Organisation guidelines during these haze events has led to increases in asthma and other respiratory problems, with high PM2.5 levels linked to an increase in risk of cancer and premature death. Large uncertainties still remain relating to the chemistry, transformation and removal rate of pollutants, particularly during haze events, meaning our ability to predict short-term pollution episodes in Beijing and other mega-cities in China, and to understand the longer term impact of mitigation measures is compromised. The wider findings of EXHALE will feed into air quality forecast and control mitigation strategies to improve the lives and health of Chinese citizens, through collaboration with our Chinese partners and by feeding into existing funded projects focussed on providing solutions for mitigating air quality degradation in China.

The results from EXHALE will be communicated to the wider scientific community via publication in high quality journals and presentations at international conferences. As detailed in the Pathways to Impact, we plan a number of engagement/communication events in China, which include a stakeholder workshop in Beijing, a training Summer School in Shanghai, and a policy brief which will be widely disseminated (for example by our Insurance company contact, AIA). Using these activities we will communicate the results of EXHALE and raise awareness to a range of stakeholders in China.

The research will be used by numerical modellers who can exploit the new data on fundamental chemical processes. This will impact sectors in China and elsewhere reliant on accurate representations in models of the fate and impact of emissions (natural and human related) in the atmosphere. These include air quality and climate policy legislators, industry, insurance companies, government advisory bodies, environment and health authorities (local and regional), and pollution forecasters. Outcomes from the modelling activities in EXHALE will inform our ability to robustly assess the health benefits of emission mitigation policies, and provide recommendations for model process improvements. Our Chinese collaborators at PKU, in particular Professor Tong Zhu, who advises the Chinese government on air quality issues, are well placed to ensure that the results and recommendations from EXHALE reach persons in positions of influence.

The PDRA in this project, as well as the visiting PhD student from PKU (Qi Zou) and visiting partner from SJTU (Yue Zhao) will benefit from using a wide range of instrumentation (lasers, optics, vacuum and gas handling, data acquisition, electronics) and modelling tools, and by working with expert investigators will receive advanced technical training and enhance their skills base considerably. The PDRA will have the opportunity to strengthen their presentation skills through communicating their research widely, both locally and to the international research community. The investigators are active within professional societies, for example the Royal Society of Chemistry, and the activities within this project will be publicised by engagement with these professional bodies. The research will also be communicated to the wider public through talks in Schools, Café Scientifique and through the media (investigators have experience and contacts with national newspapers, local media and BBC TV).