December 3, 2013

Code Oranges in Northeast due to PM 2.5.

The first image below, courtesy NOAA HMS, shows the fire locations across the United States. The red dots correspond to active fires, and the grey areas are plumes. The major concentration of fires is in the Southeast region and Pacific Northwest region. Although there is a large concentration of fires, there is little smoke being picked up by HMS. The next image shows the retrieved AOD image for the day, courtesy MODIS Terra. The image shows an increase in the northeast due to PM 2.5 formation. With a high pressure system resting over the northeast over the past few days, it is has allowed for stagnation and light winds to increase production of wintertime aerosols. A strong temperature inversion near 700 m ASL has been seen in the radiosonde data from Aberdeen Proving Ground. This temperature inversion mixed with light winds has caused stagnation that has allowed for nitrates to increase in production.


The next image, courtesy EPA AIRNOW, shows the AQI values the Mid Atlantic region. There is an increase in the AQI values due to PM 2.5 at the surface. As mentioned above, overnight temperature inversions will reduce atmospheric mixing, and light winds will limit pollutant dispersion. These conditions, combined with pollutant carryover from day to day, have yielded Unhealthy for Sensitive Groups particle levels for the region (yesterday and tomorrow as well). The next image, courtesy OMI NRT, shows the retrieved NO2 column for the troposphere. This image shows a large amount of NO2 in this same region in the Mid Atlantic/Great Lakes regions. This enhancement in column NO2 shows a strong correlation with the increase in PM 2.5 at the surface.

Posted by John Sullivan at December 3, 2013 6:34 PM
Comments

Can you explain this process to me? "...stagnation that has allowed for nitrates to increase in production." Do more nitrates actually get produced or does it mean they are just not being disbursed? Also I wanted to tell you that I noticed there was no visibility last Tues. in NJ and when I drove to Baltimore Weds - it was the same all the way. It looked like dense fog but there was no humidity. I had a friend with me who is from Sweden and he said it looked frightening. It resembled those pictures you see from China.
thanks
Gail

Posted by: Gail at December 7, 2013 7:27 PM

Gail,

With a strong temperature inversion and high pressure system it is difficult for the boundary layer to properly ventilate and disperse pollutants. The same quantity (roughly) of nitrate aerosol precursors is present but with the stagnation coupled with very cold temperatures and high humidity, these precursors have time to develop into ammonia and eventually a fine aerosol particles (PM 2.5) ammonium nitrate (NH4NO3). The OMI satellite is retrieving tropospheric nitrogen dioxide (NO2) which is one of the dominant precursors to nitrate aerosols, which is why there tends to be a strong correlation between high column amounts of tropospheric NO2 and PM 2.5 enhancement at the surface.

I am not sure about your fog situation and I am not an expert. Usually from NJ to BAL you are driving over many of the Chesapeake Bay water bodies. You may just been experiencing a temperature difference in the water and land and fog was forming. Additionally, hydroscopic salts from the bay may have helped reach the fog point if the humidity was very low by acting as a strong condensation nuclei.

Posted by: John Sullivan at December 9, 2013 8:30 AM

Gail,

With a strong temperature inversion and high pressure system it is difficult for the boundary layer to properly ventilate and disperse pollutants. The same quantity (roughly) of nitrate aerosol precursors is present but with the stagnation coupled with very cold temperatures and high humidity, these precursors have time to develop into ammonia and eventually a fine aerosol particles (PM 2.5) ammonium nitrate (NH4NO3). The OMI satellite is retrieving tropospheric nitrogen dioxide (NO2) which is one of the dominant precursors to nitrate aerosols, which is why there tends to be a strong correlation between high column amounts of tropospheric NO2 and PM 2.5 enhancement at the surface.

I am not sure about your fog situation and I am not an expert. Usually from NJ to BAL you are driving over many of the Chesapeake Bay water bodies. You may just been experiencing a temperature difference in the water and land and fog was forming. Additionally, hydroscopic salts from the bay may have helped reach the fog point if the humidity was very low by acting as a strong condensation nuclei.

Posted by: John Sullivan at December 9, 2013 8:31 AM
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