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Open biomass burning has major impacts on the Earth system, including on air quality via the emission of primary fine particulate matter (PM 2.5 ). Its effect on secondary inorganic PM 2.5 formation is comparatively little investigated. Simulations with the EMEP MSC-W WRF atmospheric chemistry transport model reveal that global biomass burning emissions lead to elevated annual mean ammonium nitrate (NH 4 NO 3 ) concentrations in densely populated regions where biomass burning mostly does not occur. These regions include eastern USA, northwestern Europe, the Indo-Gangetic Plain and eastern China, where NH 4 NO 3 conditional on biomass burning emissions constitutes between 29% and 51% of the annual mean PM 2.5 conditional on biomass burning emissions. Biomass burning emissions of CO, NO x (NO and NO 2 ) and volatile organic compounds perturb the HO x (OH and HO 2 ) cycle globally, such that there is increased oxidation of anthropogenic NO x to HNO 3 . This results in additional contributions to local-scale secondary NH 4 NO 3 in areas with high emissions of anthropogenic NO x and NH 3 . These teleconnections increase, by up to a factor of two, the contribution of biomass burning emissions to long-term PM 2.5 concentrations, which measurements alone cannot identify as an impact of biomass burning activity. This may become relatively more important as anthropogenic sources of PM 2.5 are reduced and as the wildfire component of biomass burning increases under climate change.

Open biomass burning impacts air quality through direct emissions of fine particulate matter (PM2.5) and its role in secondary PM2.5 formation. Here the interest is in the long distance and cumulative influences of biomass burning on annual mean concentrations of PM2.5 in a country far removed from major biomass burning regions: the UK. A novel, globally nested setup of the EMEP4UK atmospheric chemistry transport model is used to isolate contributions to UK PM2.5 from global biomass burning activity. Long-range influences are found to be considerable, with 0.99 µgm-3 of UK-averaged PM2.5 in 2019 being conditional on biomass burning emissions. Of this, 97 % and 73 % are associated with biomass burning outside the UK and outside the model's European domain, respectively – notably from Russia, Asia and boreal North America – which highlights the importance of boundary conditions on regional modelling setups. The simulations suggest some influences of biomass burning have lags of several weeks. The long-range component is enhanced by the role of biomass burning in secondary aerosol formation (58 % of PM2.5 conditional on biomass burning), of which 55 % is organic; the inorganic component (mainly ammonium nitrate) derives from increased oxidation of local emissions, which may be mitigated through local emissions reductions. The PM2.5 conditional on biomass burning is highly policy relevant for the UK, constituting (for 2019) 20 % of the current WHO target and 10 % of the contribution from all sources. This relative contribution is likely to increase as anthropogenic PM2.5 declines and as climate change increases northern-hemispheric extratropical biomass burning.

Open biomass burning has major impacts globally and regionally on atmospheric composition. Fire emissions include particulate matter, tropospheric ozone precursors, and greenhouse gases, as well as persistent organic pollutants, mercury, and other metals. Fire frequency, intensity, duration, and location are changing as the climate warms, and modelling these fires and their impacts is becoming more and more critical to inform climate adaptation and mitigation, as well as land management. Indeed, the air pollution from fires can reverse the progress made by emission controls on industry and transportation. At the same time, nearly all aspects of fire modelling – such as emissions, plume injection height, long-range transport, and plume chemistry – are highly uncertain. This paper outlines a multi-model, multi-pollutant, multi-regional study to improve the understanding of the uncertainties and variability in fire atmospheric science, models, and fires' impacts, in addition to providing quantitative estimates of the air pollution and radiative impacts of biomass burning. Coordinated under the auspices of the Task Force on Hemispheric Transport of Air Pollution, the international atmospheric modelling and fire science communities are working towards the common goal of improving global fire modelling and using this multi-model experiment to provide estimates of fire pollution for impact studies. This paper outlines the research needs, opportunities, and options for the fire-focused multi-model experiments and provides guidance for these modelling experiments, outputs, and analyses that are to be pursued over the next 3 to 5 years. The paper proposes a plan for delivering specific products at key points over this period to meet important milestones relevant to science and policy audiences.

Open biomass burning impacts air quality through direct emissions of fine particulate matter (PM.sub.2.5) and its role in secondary PM.sub.2.5 formation. Here the interest is in the long distance and cumulative influences of biomass burning on annual mean concentrations of PM.sub.2.5 in a country far removed from major biomass burning regions: the UK. A novel, globally nested setup of the EMEP4UK atmospheric chemistry transport model is used to isolate contributions to UK PM.sub.2.5 from global biomass burning activity. Long-range influences are found to be considerable, with 0.99 µg m.sup.-3 of UK-averaged PM.sub.2.5 in 2019 being conditional on biomass burning emissions. Of this, 97 % and 73 % are associated with biomass burning outside the UK and outside the model's European domain, respectively - notably from Russia, Asia and boreal North America - which highlights the importance of boundary conditions on regional modelling setups. The simulations suggest some influences of biomass burning have lags of several weeks. The long-range component is enhanced by the role of biomass burning in secondary aerosol formation (58 % of PM.sub.2.5 conditional on biomass burning), of which 55 % is organic; the inorganic component (mainly ammonium nitrate) derives from increased oxidation of local emissions, which may be mitigated through local emissions reductions. The PM.sub.2.5 conditional on biomass burning is highly policy relevant for the UK, constituting (for 2019) 20 % of the current WHO target and 10 % of the contribution from all sources. This relative contribution is likely to increase as anthropogenic PM.sub.2.5 declines and as climate change increases northern-hemispheric extratropical biomass burning.

Open biomass burning impacts air quality through direct emissions of fine particulate matter (PM2.5) and its role in secondary PM2.5 formation. Here the interest is in the long distance and cumulative influences of biomass burning on annual mean concentrations of PM2.5 in a country far removed from major biomass burning regions: the UK. A novel, globally nested setup of the EMEP4UK atmospheric chemistry transport model is used to isolate contributions to UK PM2.5 from global biomass burning activity. Long-range influences are found to be considerable, with 0.99 µg m−3 of UK-averaged PM2.5 in 2019 being conditional on biomass burning emissions. Of this, 97 % and 73 % are associated with biomass burning outside the UK and outside the model's European domain, respectively – notably from Russia, Asia and boreal North America – which highlights the importance of boundary conditions on regional modelling setups. The simulations suggest some influences of biomass burning have lags of several weeks. The long-range component is enhanced by the role of biomass burning in secondary aerosol formation (58 % of PM2.5 conditional on biomass burning), of which 55 % is organic; the inorganic component (mainly ammonium nitrate) derives from increased oxidation of local emissions, which may be mitigated through local emissions reductions. The PM2.5 conditional on biomass burning is highly policy relevant for the UK, constituting (for 2019) 20 % of the current WHO target and 10 % of the contribution from all sources. This relative contribution is likely to increase as anthropogenic PM2.5 declines and as climate change increases northern-hemispheric extratropical biomass burning.

Intravital imaging emerged as an indispensible tool in biological research, and a variety of imaging techniques have been developed to noninvasively monitor tissues in vivo. However, most of the current techniques lack the resolution to study events at the single-cell level. Although intravital multiphoton microscopy has addressed this limitation, the need for repeated noninvasive access to the same tissue in longitudinal in vivo studies remains largely unmet. We now report on a previously unexplored approach to study immune responses after transplantation of pancreatic islets into the anterior chamber of the mouse eye. This approach enabled (i) longitudinal, noninvasive imaging of transplanted tissues in vivo; (ii) in vivo cytolabeling to assess cellular phenotype and viability in situ; (iii) local intervention by topical application or intraocular injection; and (iv) real-time tracking of infiltrating immune cells in the target tissue.