March 24, 2009
Code Yellow PM2.5 Air Quality in Parts of Upper Midwest, Ohio River Valley, and Southeast ahead of a Low Pressure System; Code Green Elsewhere in U.S.
Air quality is Code Green (Good) across most of the nation today, as shown by the loop of PM2.5 AQI values (below).
The exception is a wide swath of Code Yellow (Moderate) PM2.5 that stretches across parts of the Upper Midwest, Ohio River Valley, and Southeast. The Code Yellow air quality is concentrated ahead of an occluded low pressure system that is currently centered over the Northern Plains states. A combination of haze and smoke from agricultural and prescribed burning, tracked on the Blog for the past few days, is likely responsible for the Moderate conditions. Today’s Terra MODIS true color image, overlaid with AQI values and current synoptic conditions in Google Earth (below on left), shows the location of the Code Yellow air quality in the vicinity of the extra-tropical cyclone, as well as an area of haze and smoke, mixed in with cloud cover, ahead of the advancing cold front. Today’s Terra MODIS AOD image (below on right) does not capture the region of haze and smoke that is evident in the true color image, due to the widespread cloud cover associated with the low pressure system. An area of slightly elevated AOD is evident in South Carolina, in a cloud-free region on the eastern periphery of the hazy and smoky airmass.
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In contrast, the New England and the Mid-Atlantic regions are enjoying clear skies and very good air quality due to a strong high pressure system centered over eastern Virginia. Today’s Terra MODIS true color image, overlaid with AQI values and current synoptic conditions in Google Earth (below on left), shows the clear skies and widespread Code Green air quality in the Northeast. It’s been somewhat unseasonably cold today and yesterday, but the clean air and bountiful sunshine have made it all worthwhile. This evening’s webcam shot from McMillan Reservoir (below on right) gives you an idea of the beautiful day we have had in Washington, DC. PM2.5 concentrations have averaged around 4 micrograms/cubic meter today at McMillan Reservoir, which is about as clean an airmass as we get in DC!
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