In order to study the mechanism of aerosol sulfate formation, weekly samples of SO2 and aerosol SO4= were collected at Hubbard Brook Experimental Forest, West Thornton, New Hampshire from July to December, 1980. Samples were analyzed for concentration and sulfur isotopes (δ34S). Late summer‐early fall samples are characterized by high, variable SO4= levels and low SO2 levels, while late fall ‐ early winter samples exhibit low SO4= and high SO2 levels. These trends suggest that the oxidation rate varies seasonally, with faster oxidation during warmer months. The sulfur isotopic fractionation between aerosol SO4= and SO2 is intermediate between that expected from homogeneous and heterogeneous reactions, indicating that both processes can be important. The isotopic data suggest that homogeneous oxidation reactions are more important than solution reactions, particularly during warm months.

Coal-related elements are toxic and persistent pollutants that have spread globally since the industrial revolution, mainly from point-source emissions. A sediment core was collected from Deep Lake in northeastern Washington State (USA) by the Washington State Department of Ecology, with the aim of assessing recent changes in atmospheric deposition in the US Pacific Northwest. The core was divided into depth intervals and dated by lead-210. A sample from each cross section was digested and analyzed for toxic metals and metalloids using inductively coupled plasma-mass spectrometry. Data show recent increases in the concentrations of arsenic, barium, selenium, and mercury. Comparison with 1993 US Geological Survey ice core data from the Upper Fremont Glacier in Wyoming (USA), Asian coal consumption data, and weather patterns suggests that pollutant inputs to Deep Lake sediments are the result of coal-burning activities in the Asia-Pacific region. Most notably, mercury deposition in Deep Lake has increased from approximately 20 ppb in 1996 to 9470 ppb in 2014 (an~400-fold increase), and since 1993 when the ice core was analyzed. Environ Toxicol Chem 2020;39:335-342. © 2019 SETAC