Importance of Inventory Representativeness for Air Quality Forecasting: A Recent North American Example

Abstract

North American air quality (AQ) forecasts made by the Environment and Climate Change Canada (ECCC) operational regional AQ prediction system since 2015 have used input emissions files based on Canadian, U.S., and Mexican national emissions inventories for base years 2010, 2011, and 1999, respectively. Since 2010, however, emissions of many criteria air pollutants have declined in both Canada and the U.S.. We recently tested new input emissions files based on a 2013 Canadian inventory, a projected 2017 U.S. inventory, and a 2008 Mexican inventory in the ECCC regional AQ prediction system. For Canada, the switch from the 2010 inventory to the 2013 inventory reduced SO₂, NO_x, and VOC annual anthropogenic emissions by 12%, 2%, and 4%, respectively. For the continental U.S., adoption of the projected 2017 inventory reduced SO₂, NO_x, and VOC annual anthropogenic emissions relative to the 2011 inventory by 65%, 33%, and 11%, respectively, suggesting the importance of emissions base-year representativeness for AQ forecasting. Moreover, the use of these new input emissions fields for 2016 and 2017 test periods improved AQ forecasts in comparison to the operational model for Canada and the U.S., in particular for summertime ozone forecasts over the eastern U.S.. A new version of the ECCC forecast system that uses these updated input emissions files was accepted for operational implementation in mid 2018.