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2 Supplemental Material Identifying changes in source regions impacting speciated atmospheric mercury at a rural site in the eastern U.S. Irene Cheng 1, Leiming Zhang 1, Mark Castro 2, and Huiting Mao 3 1 Air Quality Research Division, Science and Technology Branch, Environment and Climate Change Canada, Toronto, Ontario, Canada 2 Appalachian Laboratory, University of Maryland Center for Environmental Science, Frostburg, Maryland, U.S. 3 Department of Chemistry, State University of New York College of Environmental Science and Forestry, Syracuse, New York, U.S. Corresponding authors (irene.cheng@canada.ca or leiming.zhang@canada.ca) S1

3 Table S1: Mercury point sources and emissions in 2014 in southeastern Canada (ECCC, 2016a) and eastern U.S. (USEPA, 2016) Industries in southeastern Canada Hg emissions (kg) Proportion (%) Iron and Steel % Metals (Except Aluminum and Iron and Steel) % Cement, Lime and Other Non-Metallic Minerals % Electricity % Water and Wastewater Systems % Pulp and Paper % Aluminum % Chemicals % Waste Treatment and Disposal % Petroleum and Coal Product Refining and Mfg % Mining and Quarrying 3 0.3% Other Manufacturing 3 0.3% Wood Products % Other (Except Manufacturing) % All 1036 Industries in eastern U.S. Hg emissions (kg) Proportion (%) Electric Utilities % Primary Metals % Nonmetallic Mineral Product % Paper % Petroleum % Chemicals % Food % Fabricated Metals % Electrical Equipment % Hazardous Waste % Other % All S2

4 Figure S1: Top five types of mercury point sources in 2014 (ECCC 2016a; USEPA 2016) comprising of more than 90% of the anthropogenic mercury emissions. Refer to Table S1 for full list of the types of mercury point sources and annual emissions. S3

5 # of major source regions # of major source regions # of major source regions # of major source regions Winter GEM GOM PBM RM Spring GEM GOM PBM RM Summer Fall GEM GOM PBM RM 0 GEM GOM PBM RM Figure S2: Number of Hg source regions predicted by CWT method in each season over three time periods. Major source regions defined by the following 75 th percentile P ij (equation 1) thresholds for each season, Winter GEM: 1.45, Winter GOM: 6.47, Winter PBM: 5.31, Winter RM (GOM+PBM): 12.48; Spring GEM: 1.5, Spring GOM: 10.35, Spring PBM: 5.23, Spring RM: 15.53; Summer GEM: 1.30, Summer GOM: 5.33, Summer RM: 8.6; Fall GEM: 1.28, Fall GOM: 5.15, Fall PBM: 2.91, Fall RM: S4

6 Figure S3: Percentage change in the number of forest fires in Canada between and 2011, 2013, Forest fire point locations from Canadian Forest Service (2017). S5

7 Figure S4: Spatial distribution of predicted source intensities of PBM and fire radiative power (FRP) measured by MODIS (NASA 2017) during May to September in the and 2011, periods. 10 th, 50 th, and 90 th refer to Pij (equation 1) and FRP percentiles. S6

8 Figure S5: Percentage change in total Hg point source emissions (a,b) and powerplant Hg emissions (c,d) between and 2011, 2013, (b) and (d) are zoomed into the region close to the MD08 site. Percent changes are shown only if the absolute change is 5kg. Dec: decrease, Inc: increase. Data from ECCC (2016a) and USEPA (2016). S7

9 Figure S6: Absolute change in total Hg point source emissions (a,b) and powerplant Hg emissions (c,d) between and 2011, 2013, (b) and (d) are zoomed into the region close to the MD08 site. Dec: decrease, Inc: increase. Data from ECCC (2016a) and USEPA (2016). S8

10 Figure S7: Percentage change in predicted source intensities of GEM (Dec: decrease, Inc: increase) and regional surface temperatures from and 2011, 2013, The negative percentages/values indicate surface temperature decreases. ON: Ontario, QC: Quebec, NB: New Brunswick, NS: Nova Scotia, UM: Upper U.S. Midwest, NE: U.S. northeast, ORV: Ohio River Valley, SE: U.S. southeast. Surface temperatures from ECCC (2012) and NOAA (2017). S9

11 Figure S8: Percentage change in predicted source intensities of PBM (Dec: decrease, Inc: increase) and regional surface temperatures from and 2011, 2013, The negative percentages/values indicate temperature decreases. ON: Ontario, QC: Quebec, NB: New Brunswick, NS: Nova Scotia, UM: Upper U.S. Midwest, NE: U.S. northeast, ORV: Ohio River Valley, SE: U.S. southeast. Surface temperatures from ECCC (2012) and NOAA (2017). S10

12 Figure S9: Spatial distribution of predicted source intensities and forest fire locations (grey circles) in Canada over time. 10 th, 50 th, and 90 th refer to P ij (equation 1) percentiles. Forest fire point locations from Canadian Forest Service (2017). S11

13 Figure S10: Spatial distribution of source regions for the period. Grey circles: Hg point source emissions <10 kg yr -1 ; green circles: Hg point source emissions 10 kg yr th, 50 th, and 90 th refer to P ij (equation 1) percentiles. Emissions data from NPRI (ECCC, 2016a) and TRI (USEPA, 2016). S12

14 References Canadian Forest Service (CFS), 2017: National Fire Database Agency Fire Data. Natural Resources Canada, Canadian Forest Service, Northern Forestry Centre, Edmonton, Alberta. Accessed 10 February [Available online at Environment and Climate Change Canada (ECCC), 2012: Homogenized Surface Air Temperature Data Access, Monthly mean of daily mean temperature. Accessed 9 February [Available online at: Environment and Climate Change Canada (ECCC), 2016a: National Pollutant Release Inventory (NPRI) datasets, Bulk Data (1993 to present). Accessed 7 November [Available online at: ] NASA, 2017: MODIS/Aqua+Terra Thermal Anomalies/Fire locations 1km FIRMS V006 NRT. Accessed 26 April 2017, DOI: /FIRMS/MODIS/MCD14DL.NRT.006. NOAA National Centers for Environmental Information, 2017: Climate at a Glance: U.S. Time Series. Accessed 2 February [Available online at: USEPA, 2016: Toxics Release Inventory (TRI) Explorer. Accessed 7 November [Available online at: S13