Mobile Observations of Ozone and Aerosols in Alabama: Southeastern US Summer Pollution and Coastal Variability

We present a detailed analysis of measurements of ozone (O3) and aerosols collected using multiple platforms and instruments during a 5-day mini-campaign in Alabama, for improving our understanding of the chemistry and air quality in the Southeastern United States. Our study features the first on-road O3 lidar profiling on highways and the coordinated airborne observations that captured O3 and aerosol structures associated with synoptic weather conditions, stratospheric intrusions, wildfire smoke transport, and enhancements in urban areas. The Doppler wind lidar data suggest that the vertical structures and variability of O3 and aerosols at Dauphin Island, a coastal site in the Gulf of Mexico, were related to both the synoptic flow and local-scale land-sea breeze circulation. The onshore gulf breeze, which typically started in the afternoon, helped to quickly dilute air pollutants near the surface, resulting in large gradients toward inland areas. In contrast, gradients were much smaller on days without a gulf breeze. O3 and humidity were highly anti-correlated in the lower free troposphere, but weakly anti-correlated in the planetary boundary layer (PBL) suggesting more complicated emissions and sink of O3 in the PBL. Our on-road and airborne measurement strategies to quantify the vertical and horizontal chemical gradients will be useful for future geostationary satellite validation. Plain Language Summary We conducted a study in Alabama to measure ozone, aerosol, and meteorological variables using ground-based, mobile, and airborne systems. Our study included the first use of a mobile ozone lidar, a remote sensing instrument, collecting data while driving on highways. The lidar captured the ozone structures related to urban emissions, weather conditions, and fire smoke transported from remote locations. We found that the distributions and variations of ozone and aerosols at Dauphin Island (DI), a coastal site in the Gulf of Mexico, were influenced by both large-scale weather patterns and local winds called sea breeze that blow from the land to the sea in the morning and reverse the direction in the afternoon. We found the sea breeze helped to improve the air quality at DI, different from other megacities with much higher pollution. However, the sea breeze resulted in significant horizontal ozone differences, similar to other locations. We found a strong negative relationship between ozone and humidity at higher altitudes, but a weaker negative relationship at lower altitudes due to more complex emissions and loss of ozone at the surface. Our techniques to measure ozone and aerosol gradients vertically and horizontally will be valuable for evaluating future satellite observations.