Global impacts of particulate matter air pollution

Even in well-studied, data-rich regions of the United States and Europe, understanding ambient particulate matter (PM, aka aerosols) remains a challenge. Atmospheric aerosols exhibit chemical heterogeneity, spatial and seasonal variability, and result in a wide range of health impacts (mortality, respiratory disease, cardiovascular disease, eye irritation, and others). In addition, aerosols play an important role in climate, exerting warming effects (black carbon), cooling effects (sulfate and organic carbon), and affecting precipitation and cloud cover. Characterizing the emission sources, concentrations, transport patterns, and impacts is particularly difficult in developing countries, where data are scarce, emissions are high, and health impacts are often severe. We are pleased to present this focus issue of Environmental Research Letters (ERL) devoted to the study of PM on an international scale. Our authors are leading researchers who each bring cross-cutting analysis to this critical health and environmental issue. Collectively, the research presented here contributes to our understanding of PM sources, processes, and impacts, while highlighting key steps forward. In this issue, Zhang et al examine the size distribution and composition of emitted anthropogenic PM in China, finding that the characteristics of primary aerosol emissions differ significantly between industrialized and developing regions in China. Concentration measurements of PM, like detailed emissions inventories, are rare in the developing world. van Vliet and Kinney analyze fine particles in Nairobi based on monitoring data for PM2.5 and black carbon. Using measurements from multiple locations of differing proximity to roadways, the authors evaluate traffic-source contributions to PM exposure. The impact of emission location and exposed population are also evaluated by Liu and Mauzerall, but on a continent-to-continent scale. The authors quantify the connection between SO2 emissions and sulfate aerosol exposure (both domestically and on downwind continents), while presenting a new metric to quantify the impact of distance on health-relevant exposure: the 'influence potential'. Extending the scope of aerosol impacts from health to climate, Bond outlines the barriers to including aerosols in climate agreements, and proposes solutions to facilitate the integration of this key climate species in a policy context. Together, the articles scope out the state-of-the-science with respect to key issues in international air pollution. All four studies advance understanding the human health implications of air pollution, by drawing from worldwide data sources and considering a global perspective on key processes and impacts. To extend exposure estimates, like those of van Vliet and Kinney or Liu and Mauzerall, and to evaluate the induced physiological response of PM exposure, typically existing dose?response relationships are applied. Unfortunately, the common practice of applying health response estimates from one location to another is problematic. In addition to potential differences in the chemical composition of particles, the underlying populations may differ with respect to their baseline health status, occupational exposures, age and gender distribution, and behavioral factors such as nutrition and smoking habits. Health response to a given stressor is affected by the quality of and access to health care, which varies widely, and can be almost non-existent in some regions of developing countries. Further, exposure to ambient PM is affected by the relative fraction of time spent in different settings (e.g., work, home, outside, in transit), the activities that affect ventilation rate (e.g., exercising heavily versus sitting still), and housing characteristics that alter the penetration of outdoor particles into indoor environments (e.g., housing materials, windows, air conditioning). To make the most of exposure estimates, the 'missing link' is the development of dose?response relationships that take into account how the high degree of source and demographic variability affect PM health response. We look forward to the continued growth of research in ERL contributing to air pollution emissions, distribution, and impacts. As the integrated study of air quality connects to economics, energy, agriculture, meteorology, climate change, and public health?among other subjects?its advancement is well-suited to an interdisciplinary, open-access journal like ERL. Thanks to our authors for contributing to ERL's growth in global air pollution research with such excellent work. Focus on Global Impacts of Particulate Matter Air Pollution Contents The articles below represent the first accepted contributions and further additions will appear in the near future. Major components of China's anthropogenic primary particulate emissions Qiang Zhang, David G Streets, Kebin He and Zbigniew Klimont Impacts of roadway emissions on urban particulate matter concentrations in sub-Saharan Africa: new evidence from Nairobi, Kenya E D S van Vliet and P L Kinney Potential influence of inter-continental transport of sulfate aerosols on air quality Junfeng Liu and Denise L Mauzerall Can warming particles enter global climate discussions? Tami C Bond