Observations and impacts of transported Canadian wildfire smoke on ozone and aerosol air quality in the Maryland region on June 9–12, 2015

ABSTRACT

Canadian wildfire smoke impacted air quality across the northern Mid-Atlantic (MA) of the United States during June 9–12, 2015. A multiday exceedance of the new 2015 70-ppb National Ambient Air Quality Standard (NAAQS) for ozone (O₃) followed, resulting in Maryland being incompliant with the Environmental Protection Agency’s (EPA) revised 2015 O₃ NAAQS. Surface in situ, balloon-borne, and remote sensing observations monitored the impact of the wildfire smoke at Maryland air quality monitoring sites. At peak smoke concentrations in Maryland, wildfire-attributable volatile organic compounds (VOCs) more than doubled, while non-NOx oxides of nitrogen (NOz) tripled, suggesting long range transport of NOx within the smoke plume. Peak daily average PM_2.5 was 32.5 µg m⁻³ with large fractions coming from black carbon (BC) and organic carbon (OC), with a synonymous increase in carbon monoxide (CO) concentrations. Measurements indicate that smoke tracers at the surface were spatially and temporally correlated with maximum 8-hr O₃ concentrations in the MA, all which peaked on June 11. Despite initial smoke arrival late on June 9, 2015, O₃ production was inhibited due to ultraviolet (UV) light attenuation, lower temperatures, and nonoptimal surface layer composition. Comparison of Community Multiscale Air Quality (CMAQ) model surface O₃ forecasts to observations suggests 14 ppb additional O₃ due to smoke influences in northern Maryland. Despite polluted conditions, observations of a nocturnal low-level jet (NLLJ) and Chesapeake Bay Breeze (BB) were associated with decreases in O₃ in this case. While infrequent in the MA, wildfire smoke may be an increasing fractional contribution to high-O₃ days, particularly in light of increased wildfire frequency in a changing climate, lower regional emissions, and tighter air quality standards.

Implications: The presented event demonstrates how a single wildfire event associated with an ozone exceedance of the NAAQS can prevent the Baltimore region from complying with lower ozone standards. This relatively new problem in Maryland is due to regional reductions in NOx emissions that led to record low numbers of ozone NAAQS violations in the last 3 years. This case demonstrates the need for adequate means to quantify and justify ozone impacts from wildfires, which can only be done through the use of observationally based models. The data presented may also improve future air quality forecast models.

Funding

The authors gratefully acknowledge support for this study provided by UMBC/JCET (Task 374, Project 8306), the Maryland Department of the Environment (MDE, contract U00P4400079), the NOAA-CREST CCNY Foundation (subcontract 49173B-02). Publication charges for this paper were paid by ARL.

Additional information

Funding

The authors gratefully acknowledge support for this study provided by UMBC/JCET (Task 374, Project 8306), the Maryland Department of the Environment (MDE, contract U00P4400079), the NOAA-CREST CCNY Foundation (subcontract 49173B-02). Publication charges for this paper were paid by ARL.

Notes on contributors

Joel Dreessen

Joel Dreessen serves as a meteorologist at the Maryland Department of the Environment with the air monitoring program in Baltimore, MD.

John Sullivan

John Sullivan is a currently a postdoctoral fellow under Dr. Thomas J. McGee in the Atmospheric Chemistry and Dynamics Laboratory at NASA Goddard Space Flight Center in Greenbelt, MD.

Ruben Delgado

Ruben Delgado is an assistant research scientist of the Joint Center of Earth Systems Technology at the University of Maryland Baltimore County, Baltimore, MD.