Authors Dr Kathryn M Emmerson Dr Kathryn Emmerson is a Principal Research Scientist at CSIRO, interested in how emissions of gases and particles affect local and regional air quality. She is an expert in developing new parameterisations for atmospheric chemistry models, including the CSIRO Chemical Transport Model (C-CTM). She has worked on a diverse range of air quality problems involving smoke, secondary organic aerosol, inorganic chemistry on sea salt aerosol, pollen, mercury, and biogenic gas phase emissions. Dr Emmerson represents Australian research interests on the Southern Hemisphere Working Group of International Global Atmospheric Chemistry. Dr Melita D Keywood Dr Melita Keywood is a Senior Principal Research Scientist in the Climate Science Centre of the Oceans of CSIRO. Melita’s research expertise lies in the chemical and microphysical properties of atmospheric aerosol, which she uses in a variety of applications ranging from tracking long term changes in aerosol microphysics and chemical composition of the remote marine boundary layer, to understanding aerosol growth and secondary organic aerosol in urban airsheds and biomass burning plumes. Dr Keywood was the 2019 recipient of the Werner Strauss Clean Air Achievement Award from the Clean Air Society of Australia and New Zealand and is the President of the International Commission on Global Pollution and Atmospheric Chemistry. Body Acknowledgements We would like to acknowledge the assistance of many people who provided data, case studies and photographs, and who reviewed the draft chapter. We would particularly like to thank: Stephanie Beaupark, University of Wollongong Belinda Brown, Australian Government Department of Agriculture, Water and the Environment Rebecca Buchholz, National Center for Atmospheric Research, United States Jason Choi, Environment Protection Authority Victoria Jacinta Cooper, CSIRO Beth Ebert, Bureau of Meteorology Rosemary Fedele, Environment Protection Authority Victoria Ian Fox, Australian Capital Territory Health Directorate Markus Froehlich, ACT Health Directorate Christy Geromboux, University of Sydney Alan Griffiths, Australian Nuclear Science and Technology Organisation Elise A Guerette, CSIRO Ivan Hannigan, University of Sydney Melissa Hart, University of New South Wales John Innis, Environment Protection Authority, Tasmania Paul Krummel, CSIRO Ray Langenfelds, CSIRO Don Neale, Queensland Department of Environment and Science Luke Pinner, Australian Government Department of Agriculture, Water and the Environment Matt Riley, New South Wales Department of Planning, Industry and Environment Pushan Shah, South Australian Environment Protection Authority Richard Smart Sean Watt, New South Wales Department of Planning, Industry and Environment Robyn Schofield, University of Melbourne National Air Quality Technical Advisory Group.