Remote Sensing and Ground Integrated Observing System to Assess the Impact of Nocturnal Low Level Jets on the Air Quality in Baltimore, MD

Coastal regions in the United States (US) are home to 40% of the nation's total population. However, previous coastal studies from the surface to three kilometers, have not fully characterized the spatial and diurnal variability of the influence of boundary layer dynamics on chemistry. Summer months air quality (AQ) events in the Mid-Atlantic US are known to be influenced by the intrusion of Nocturnal Low Level Jets (NLLJ) into the nocturnal boundary layer. NLLJs are capable of transporting atmospheric constituents hundreds of kilometers and in some cases are associated with high concentrations of pollutants at the surface. Weather conditions during May 19-23, 2021 were conducive to development of NLLJs in the Mid-Atlantic US. Many sites in the region observed multiple exceedances of the EPA's National Ambient Air Quality Standard of ozone. The ability to accurately predict weather and AQ depends on detailed knowledge of boundary layer dynamics and composition in a four-dimensional (4D) observation framework, which is currently lacking in the US. This analysis leveraged multiple platforms including the NASA Tropospheric Ozone Lidar Network (TOLNet), Pandora spectrometers, AErosol RObotic NETwork (AERONET), ceilometers, radar wind profilers, AQ surface monitors, and met- and ozone-sondes; in addition to simulations of pollutant transport by NOAA's Hybrid Single-Particle Lagrangian Trajectory (HYSPLIT) model. HYSPLIT back-trajectories initiated from the center of the polluted boundary layer show recirculation of regional airmass and longer-range transport of aerosols and ozone precursors. Adding to the local/regional pollutant re-distribution, NLLJs were observed which had significant impacts on the downmixing of ozone from residual layer to surface layer. The Integrated Observing System allows for the examination and characterization of local and regional dynamics phenomena, and their coupling and evolution of chemical budgets that impacts AQ. The following questions will be discussed: (Q1) What is the spatiotemporal variability of particle pollution and trace gases during the NLLJ? (Q2) What effect do key boundary layer dynamic processes have on the forecasting and simulation of particle pollution and trace gases?