U.S. Air Quality

Weekend Lidar Observation of Pollution over Baltimore

This weekend’s weather in the US Mid-Atlantic states was dominated by a high pressure system. Warm air aloft, increasing moisture and strong surface temperature inversion enhanced particle matter formation throughout the weekend. Surface temperature inversions play a major role in air quality, especially during the winter when these inversions are the strongest. The warm air aloft on top of cooler air acts like a lid, suppressing vertical mixing and trapping the cooler air at the surface. As pollutants are emitted into the air, the inversion traps these pollutants near the ground, leading to poor air quality. A strong inversion will confine pollutants to a shallow vertical layer.

ELF operated continuously for 61 hours to monitor this wintertime pollution event (Kudos: to my fellow co-workers) From the lidar timeseries we can see that besides the occasional clouds advecting over UMBC (red dots over 1.5 km) that the greatest amount of particulate scattering occurred within the first 650 meters of the troposphere (aqua to red counts). The three occasion when the increase of photons scattered back to the lidar receiver was greater temporally coincides to the increase in PM2.5 concentrations recorded at the Maryland Department of the Environment Oldtown monitoring station in Baltimore, according to the data provided by EPA’s AirNowTech site. There is a 5 hour difference between GMT (shown as UTC in lidar timeseries) and EST, therefore 15:00 UTC corresponds to 10:00 am EST, in order to make the proper temporal comparison.

On a interesting note, I would like to point out that ELF is a two channel lidar system that allows to obtain polarization and color ratio of natural and human-made aerosol particles in the atmosphere. ELF is currently configured to obtain polarization ratios. The polarization ratio allows two categorize aerosol into two categories: spherical and non-spherical. Haze and forest fire smoke particles are examples of the former, and desert dust and biogenic debris (e.g., pollen) of the latter. The figure below shows the vertical and temporal distribution of these non-spherical particles. Road-salt dust might a possible source for the non-spherical particles observed. As the salt gets abraded from the roads is launched into the atmosphere. PM sampling at UMBC has been carried out since Friday as part of the new Experimental Atmospheric Physics course developed by Dr. J. Martins Vanderlei and Dr. Manfredo Tabacniks. Results of their analysis will be posted on this blog as they become available and will aid in the identification of particulate matter.