July 31, 2008
It can be as hazy in Baltimore as in Beijing in lidar (but that's misleading)
Yesterday, we had a haze event that Ruben logged on the blog with the lidar and Erica described. The CALIPSO expedited images (below) show that at 39oN the aerosol return is as strong as it was over China a few days ago on a prior posting.
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The strong backscattering, however, is probably due to the humidification of the aerosol since the actual PM2.5 concentration is only slightly into the unhealthy for sensitive people range (Baltimore Old Town data and the Howard University Beltsville site).
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UPDATE: (8/1/08) As a check on this, I pulled the AERONET Level 1.0 (uncorrected for clouds) column optical depths in Baltimore (left, MD Science Center, credit Brent Holben, PI) and right (Beijing, courtesy Hong-bin Chen and Phillipe Goloub, PIs) and while MD (ignore the ultraviolet channels in blue which are strange) has optical depths from 1-2 during our haze event here, Beijing is repetitively and continuously over 1 in optical depth and as high as four. For new readers, the amount of sunlight reaching the surface is decreased by a factor e-AOD) and e-4 = 0.018 or only 2% of the direct sunlight is reaching the ground. Since the difference in optical depth varies between 2 and 4 during these events between Baltimore and Beijing, the actual attenuation through the atmosphere is a factor of 3 to 20 higher in Beijing.
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