MULTI-DAY LIDAR OBSERVATIONS DURING A SUMMERTIME WILDFIRE AND OZONE ENHANCEMENT EPISODE

A unique multi-day air quality event occurred throughout the Mid-Atlantic region from June 9-12, 2015. For Maryland, the surface concentrations of ozone observed throughout June 11, 2015 corresponded to the worst air quality day since the pre-Derecho event on June 29, 2012. The June event was coupled to the advection of widespread smoke and debris from western Canada throughout the region. Observations indicated that the aged smoke impacted the Planetary Boundary Layer (PBL) and greatly enhanced ozone concentrations at the surface. Poor air quality was likely exacerbated by synoptic meteorology bringing light winds and sunny skies throughout the time period. Many ground sites in the region, particularly in Maryland, recorded 8-hr ozone concentrations that were in exceedance of the 75 ppb EPA National Ambient Air Quality Standard (NAAQS). However, the ozone exceedances were delayed as compared to the onset of the smoke, which suggests complex photochemistry within the region likely played a significant role in ozone formation.

During this event, nearly continuous vertical profiles of ozone are presented at Beltsville, MD from the NASA Goddard Space Flight Center TROPospheric OZone DIfferential Absorption Lidar (GSFC TROPOZ DIAL), which has been developed and validated within the Tropospheric Ozone Lidar Network (TOLNet). Additional measurements of surface ozone, aerosol lidar profiles, wind profiles, and balloon borne profiles are also presented. The air quality forecasts for the region are also presented for the surface layer. Although quantifying ozone increases in the PBL during air quality episodes has been historically difficult, results indicate mostly well mixed ozone concentrations between 90 and 120 ppbv during the daytime on June 11, 2015 . Though well mixed, surface ozone concentrations remained much lower. Amplified above-surface ozone concentrations also persisted for a longer duration than the surface concentrations. Furthermore, although surface monitors during the nighttime from June 11 to June 12 2015 indicated low ozone concentrations around 30 ppbv, a residual layer of ozone aloft, between 70 – 85 ppbv, was observed overnight.