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. The Newton Fund builds research and innovation partnerships with developing countries across the world to promote the economic development and social welfare of the partner countries.