Cities in South and Southeast Asia are developing rapidly without routine, up-to-date knowledge of air pollutant precursor emissions. This data deficit can potentially be addressed for nitrogen oxides (NOx) by deriving city NOx emissions from satellite observations of nitrogen dioxide (NO2) sampled under windy conditions. NO2 plumes of isolated cities are aligned along a consistent wind-rotated direction and a best-fit Gaussian is applied to estimate emissions. This approach currently relies on non-standardized selection of the area to sample around the city centre and Gaussian fits often fail or yield non-physical parameters. Here, we automate this approach by defining many (54) sampling areas that we test with TROPOspheric Monitoring Instrument (TROPOMI) NO2 observations for 2019 over 19 cities in South and Southeast Asia. Our approach is efficient, adaptable to many cities, standardizes and eliminates sensitivity of the Gaussian fit to sampling area choice, and increases success of deriving annual emissions from 40-60% with one sampling area to 100% (all 19 cities) with 54. The annual emissions we estimate range from 16±5 mol s-1 for Yangon (Myanmar) and Bangalore (India) to 125±41 mol s-1 for Dhaka (Bangladesh). With the enhanced success of our approach, we find evidence from comparison of our top-down emissions to past studies and to inventory estimates that the wind rotation and EMG fit approach may be biased, as it does not adequately account for spatial and seasonal variability in NOx photochemistry. Further methodological development is needed to enhance its accuracy and to exploit it to derive sub-annual emissions.

The strategies that policymakers take to mitigate climate change will have considerable implications for human exposure to air quality, with air quality co-benefits anticipated from climate change mitigation. Few studies try to model these co-benefits at a regional scale and even fewer consider health inequalities in their analyses.   We analyse the health impacts across Western and Central Europe from exposure to fine particulate matter (PM2.5) and surface level ozone (O3) in 2014 and in 2050 using three scenarios with different levels of climate change mitigation, using a high-resolution atmospheric chemistry model to simulate future air quality. We use recent health functions to estimate mortality related to the aforementioned pollutants. We also analyse the relationship between air quality mortality rate per 100,000 people and Human Development Index to establish if reductions in air quality mortality are achieved equitably.   We find that air quality-related mortality (PM2.5 + O3 mortality) will only reduce in the future following a high-mitigation scenario (54%). It could increase by 7.5\% following a medium-mitigation scenario and by 8.3% following a weak mitigation scenario. The differences are driven by larger reductions in PM2.5-related mortality and a small reduction in O3-related mortality following the sustainable scenario, whereas for the other scenarios, smaller improvements in PM2.5-related mortality are masked by worsening O$_3$-related mortality.   We find that less developed regions of European countries have higher mortality rates from PM2.5 and O3 exposure in the present day, but that this inequity is reduced following greater climate change mitigation.

Past emission controls in the UK have substantially reduced precursor emissions of health-hazardous fine particles (PM2.5) and nitrogen pollution detrimental to ecosystems. Still, 79% of the UK exceeds the World Health Organization (WHO) guideline for annual mean PM2.5 of 5 μg m-3 and there is no enforcement of controls on agricultural sources of ammonia (NH3). NH3 is a phytotoxin and an increasingly large contributor to PM2.5 and nitrogen deposited to sensitive habitats. Here we use emissions projections, the GEOS-Chem model, high-resolution datasets, and contemporary relationships between exposure and risk of harm to assess the potential human and ecosystem health co-benefits in 2030 relative to the present day of adopting legally required or best available emission control measures. We estimate that present-day annual adult premature mortality attributable to exposure to PM2.5 is 48,625, that harmful amounts of reactive nitrogen deposit to almost all (95%) sensitive habitat areas, and that 75% of ambient NH3 exceeds levels safe for bryophytes. Legal measures decrease the extent of the UK above the WHO guideline to 58% and avoid 6,800 premature deaths by 2030. This improves with best available measures to 36% of the UK and 13,300 avoided deaths. Both legal and best available measures are insufficient at reducing the extent of damage of nitrogen pollution to sensitive habitats, as most nitrogen emitted in the UK is exported offshore. Far more ambitious reductions in nitrogen emissions (>80%) than is achievable with best available measures (34%) are required to halve excess nitrogen deposition to sensitive habitats.