July 23, 2012
Very Unhealthy Ozone conditions in Michigan; Saharan dust marches west
Michigan experienced Very Unhealthy (Code Purple) surface ozone conditions today, juxtaposed to its large lake. Moderate levels remained throughout the night and early morning for much of the Great Lake region, however ozone conditions particularly escalated over the western portion of Michigan (bottom left, courtesy AIRNow). Readings from the communities affected were in the triple digits, as seen for the town of Coloma which experienced the highest level of 125 ppb at 6PM (LST) before finally abating (bottom right).
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Particulates did not significantly impact air quality across the US today, and the majority of the nation remained in the Good- Moderate AQI range. The HMS analysis team mentioned the presence of dust from Africa's largest desert, the Sahara, over the Southeast. This swath of dust traversed thousand of miles over the Atlantic ocean, which is not unusual since the continent typically experiences its largest dust outbreaks during boreal summer season (JJAS). NASA's LANCE Web Mapping Service provides us with a fantastic image from the MODIS sensor aboard the Tera satellite depicting two substantial regions of elevated AOD- one streaming off West Africa and the other adjacent to the West Tropical Atlantic, near the US's eastern shoreline (bottom).
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NOAA's HYSPLIT backward airmass trajectory for the previous 48hours suggests the airmass over Georgia originated from a south/southeasterly track, further supporting the notion that Saharan dust has reached this area (bottom left). Albeit, NOAA's Ocean Prediction Center's 48-hour mid-level atmosphere forecast implies that dust from the broad envelop of dust over the western Atlantic could progress further towards the US, as clockwise circulation and stable conditions will likely continue due to a high pressure system progresses west (bottom right).
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