Using operational HMS smoke observations to gain insights on North American smoke transport and implications for air quality

Abstract

Wildfires represent a major challenge for air quality managers, as they are large sources of particulate matter (PM) and ozone (O3) precursors, and they are highly dynamic and transient events. Smoke can be transported thousands of kilometers to deteriorate air quality over large regions. Under a warming climate, fire severity and frequency are likely to in- crease, exacerbating an existing problem. Using the National Environmental Satellite, Data and Information Service (NESDIS) Hazard Mapping System (HMS) smoke data for the U.S. and Canada for the period 2007 to 2014, I examine a subset of fires that are confirmed to have produced sufficient smoke to warrant the initiation of a National Weather Service smoke forecast. The locations of these fires combined with Hybrid Single Particle Lagragian Integrated Trajectory Model (HYSPLIT) forward trajectories, satellite detected smoke plume data, and detailed land-cover data are used to develop a climatology of the land- cover, location, and seasonality of the smoke that impacts the atmospheric column above 10 U.S. regions. I examine the relative contribution of local versus long-range transport to the presence of smoke in different regions as well as the prevalence of smoke generated by agricultural burning versus wildfires. This work also investigates the influence of smoke on O3 abundances over the contiguous U.S. Using co-located observations of particulate matter and the NESDIS HMS smoke data, I identify summertime days between 2005 and 2014 that Environmental Protection Agency Air Quality System O3 monitors are influenced by smoke. I compare O3 mixing ratio distributions for smoke-free and smoke-impacted days for each monitor, while accounting for temperature. This analysis shows that (i) the mean O3 abundance measured on smoke-impacted days is higher than on smoke-free days at 20% of monitoring locations, and (ii) the magnitude of the difference between smoke-impacted and smoke-free mixing ratios varies by location and is sensitive to the minimum temperature allowed for smoke-free days. For each site, I present the percentage of days when the 8-hr average O3 mixing ratio (MDA8) exceeds 75 ppbv and smoke is present. When our most lenient temperature criteria are applied to smoke-free days, smoke-impacted O3 mixing ratios are most elevated in locations with the highest emissions of nitrogen oxides. The Northeast corridor, Dallas, Houston, Atlanta, Birmingham, and Kansas City stand out as having smoke present 10-20% of the days when 8-hr MDA8 O3 mixing ratios exceed 75 ppbv. Most U.S. cities maintain a similar proportion of smoke-impacted exceedance days when they are held against the new MDA8 limit of 70 ppbv.