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Boston
Photo Gallery
Examples of good & bad days |
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Several examples are presented below
of the types of visibility days that tend to occur in
Boston. These include clear days, "hazy" polluted days,
"brown cloud" polluted days, and naturally-impaired
days, such as those with heavy fog or clouds.
For each picture, fine particle
(PM2.5) concentrations and relative humidity (RH) levels
are provided for reference. These variables tend to
have the biggest affect on visibility.
Click on a picture to view
a larger version.
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Clear Day
July 11, 1999
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Clear
Day
June 16, 1999
This is a typical clean, clear day in Boston. Note
the crispness of the features on the horizon. These
days will have low pollution levels and low humidity.
PM2.5 = 4.8 ug/m3
RH = 19%
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Hazy Polluted Day
June 7, 1999
This is a typical hazy polluted day in Boston. Note
the relatively uniform white haze that obscures the
horizon. The haze tends to diminish slightly at higher
elevations. These events tend to occur on hot and humid
summer days and are affiliated with high ozone, PM2.5,
and RH levels.
PM2.5 = 16.7 ug/m3
RH = 45%
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Brown
Cloud Polluted Day
January 21, 1999
This is a typical "brown cloud" polluted day in Boston.
Note how the brown cloud appears to envelop the city
but quickly thins out at higher elevations. These events
tend to occur on calm winter mornings during rush hour
traffic. PM2.5 and black carbon levels may be high;
ozone will be low; RH may vary.
PM2.5 = 40+ ug/m3
RH = 69%
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Foggy Day
June 13, 1999
This is an example of a foggy day in Boston. It appears
similar to a hazy polluted day, but note how the fog
tends to be more grey than the white haze and how it
does not thin out near the top of the picture. Fog is
most common in the fall and spring. RH will be very
high; ozone will be low; PM2.5 may be moderate or high
since the fog may trap local pollutants.
PM2.5 = 15 ug/m3
RH = 98%
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