As noted by Graham yesterday, we have a high NO₂ event going on in the midwest. The flow is blocked by an offshore high pressure area off the east coast so nothing is moving quickly. The high PM concentrations seen in the southern Great Lakes yesterday are worse on Saturday on now we are seeing some code red conditions below the bank of clouds in the region. We will watch this as it moves through the east tomorrow and Maryland Department of Environment has asked for lidar profiles at UMBC this weekend.

We also have a couple on interesting weather features on Saturday. In North Dakota, a line of low cloud/fog is seen and you can see a gravity wave feature that is nucleating these clouds. Off the West Coast, the drought is starting to get some relief but this weekend the "Atmospheric River" is flowing into Washington state.

The NOAA HMS Smoke and Fire Product saw no significant fires today, although the MODIS Aqua satellite image (top left) shows elevated AOD in the Great Lakes. The EPA AIRNow combined AQI loop (top right) depicts moderate to USG AQI in the Great Lakes and Midwest today along with moderate AQIs smattered across the United States. The current high AQI is in Rochester, MN (135) with South Bend, IN being a close second (130).

The OMI NRT tropospheric NO2 column (bottom left) helps explain the raised AQIs in the Great Lakes and upper Midwest, as high levels of NO2 were seen over these regions. Also, going back to the MODIS Aqua image, cloud cover prohibited data over places such as Wisconsin and Minnesota, where some of the highest AQIs have been seen. To the bottom right is a webcam image overlooking St. Paul, MN. From this photo one can see overcast skies, which have persisted throughout the day, and decreased visibility in the area. The main culprit of the AQIs in the area is PM2.5, so it is possible that the low clouds have trapped some of the NO2 concentrations and other aerosols, causing the AQI to increase.

Moderate AQI levels were reported by AirNow in the Mid-Atlantic, Great Lakes, and part of the Mississippi Valley throughout the day (top left). In addition, unhealthy levels for sensitive groups were reached during the afternoon in the great lakes region. High NO2 levels were retrieved by OMI in the Mid-Atlantic and Great Lakes regions (top right). According to HMS, no significant fires were detected today.

International Feature: Cape Verde Under Dust

When the winds of winter sweep across West Africa, temperatures drop and skies turn yellow. Prevalent from November to March, the harmattan is a desert wind that blows across the Sahara Desert from the northeast or the east, usually as a result of a high pressure system over the northwestern Sahara. Harmattan winds pick up dust and darken skies.
A harmattan dust storm was blowing on February 28, 2014, when the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite acquired this image. The yellow dust was concentrated largely over the Cape Verde Islands, where the mountain topography created swirling eddies and triangular wakes in the dust cloud. West Africa frames the right edge of the image, and distinct plumes of dust moved west from Senegal and Mauritania.
The dust storm had a long reach. By March 4, a faint yellow haze lingered over the Caribbean.
The storm is not unusual in its reach. Hundreds of millions of tons of dust blow out of Africa every year, reaching the Atlantic, Caribbean, and Gulf of Mexico. The dust fertilizes ocean waters, feeding plankton growth, but it may also carry fungus and disease-causing microorganisms that damage coral reefs. On land, the dust is a health hazard when inhaled, and it has been found to carry chemical contaminants, including pesticides.

NOAA Hazard Mapping System Fire and Smoke Product reported the presence of very light density dust. Dust was lifted into atmosphere in response to a rear descending jet behind the upper low over New Mexico and western Texas. AOD from MODIS Aqua shows high values over New Mexico. Optical column size distribution retrieved from AERONET White Sands_HELSTF sun photometer how the presence of coarse particulate (radius in the range of 1-10 microns) aloft.

EPA's Airnow animation shows Moderate PM2.5 AQI levels along the eastern half of the US. Surface inversion limited mixing and contribute to rising particle concentrations.Code Orange AQI levels were reported in Idaho. Tropospheric NO2 retrievals (courtesy OMI KNMI) show high concentrations over California, Illinois, Ohio and the New England region.

Clouds cover most of the U.S., as seen in the Aqua MODIS imagery below (top left), so satellite measurements aren't going to provide much information about air quality. Surface observations are unimpaired, and a collection of these from the EPA (top right) indicates Moderate AQI levels across the eastern part of the midwest, along the Mason-Dixon line up into Pennsilvania, southern California, and northern Idaho, with one station reporting AQI levels Unhealthy for Sensitive Groups (bottom left). HMS Fire and Smoke Analysis imagery (bottom right) indicates patches of fires along the Kansas - Missouri border and in central Florida.

What tropospheric NO2 data is available from OMI indicates that Secondary Nitrate may be behind the elevated AQI in the east. The low wind speeds across the eastern United States indicate that whatever aerosols are in the area are going to stay for a while with little to move them out.

Today air quality was in the Code Yellow (Moderate) range across large portions of the Northeast, Mid-Atlantic, and Southeast, as well as scattered readings across the Great Lakes, Pacific Northwest and Rocky States (top left). The highest PM2.5 readings today were observed in southern North Carolina, peaking in Code Orange (Unhealthy for Sensitive Groups) range. The HMS analysis team reports several fires across Florida and several associated plumes of smoke (top right). A single fire was also observed across southern North Carolina, which could have contributed to the raised PM2.5 readings there. However, the MODIS sensor onboard the Terra satellite, could not demonstrate clear AOD observations in this region due to expansive cloud cover (bottom left). The NAAPS aerosol model indicates air quality in these regions could continue to be poor, as elevated sulfate across Great Lakes, Mid-Atlantic, Northeast by Wednesday, ranging between 2-8 micrograms per cubic meter are forecast. Finally, March came in like a lion this year for parts of the Mid-West, Mid-Atlantic, and Northeast with strong winter storm bringing these regions to a standstill yet again. The same system that brought the West Coast it's record rainfall last week dumped several inches of snow across the aforementioned regions, and funneled in an Arctic air mass that caused temperatures to plummet to record levels for some areas tonight.

The AIRNOW AQI for the day shows that there are code orange AQI readings in Utah, Georgia and Pennsylvania. The HMS Smoke assessment shows fires throughout the US southeast and plumes evident throughout Georgia. Below that there is a fire near Lake Okeechobee in Florida.