Page 391 - Fundamentals of Air Pollution 3E

346 21. Air Pollution Climatology

TABLE 21-1
Hourly Surface Observation Variables
Station number, five digits"
Date—year, month, day, six digits"
Hour, two digits"
Ceiling height, hundreds of feet, three alphanumeric characters"
Sky condition, up to four layers, four alphanumeric characters
Visibility, miles, three digits (coded)
Weather and/or obstructions to vision, eight alphanumeric characters
Sea-level pressure, millibars, four digits
Dew point, °F, three digits
Wind direction, tens of degrees azimuth, two digits"
Wind speed, knots, two digits"
Station pressure, inches of mercury, four digits
Dry bulb temperature, °F, three digits"
Wet bulb temperature, °F, three digits
Relative humidity, percent, three digits
Clouds and obscuring phenomena
Total amount, tenths, one coded alphanumeric character"
Following for up to four layers:
Amount, tenths, one coded alphanumeric character
Type, one coded alphanumeric character
Height, hundreds of feet, three alphanumeric characters
Amount of opaque cloud cover, tenths, one alphanumeric character"
" Of particular interest in air pollution work.

Other data, gathered primarily once each day by cooperative observers,
consist mostly of temperature and precipitation readings. These are of
limited usefulness for air pollution analysis because wind data are generally
lacking.
Other sources of data, especially wind data, may be routinely measured
by industrial or commercial establishments. Availability of these data must
be ascertained through contact with each data collector.
Many city and regional agencies responsible for air pollutant measure-
ments also measure wind and temperature at some of their air pollutant
sampling stations. Because exposure at air quality stations is generally
considerably less ideal than at airport stations, the data may be representa-
tive of extremely local conditions.
Radiosonde balloons are released twice daily, near 00 and 12 GMT. Mea-
surements of temperature and humidity, alternated by a pressure switch,
are transmitted by radio signals from the instrument package, which is
also tracked by ground-based radio direction-finding equipment at the point
of release. This allows computation of wind direction and wind speed
at numerous heights above ground. Figure 21-1 shows the locations of
radiosonde stations throughout the world, including over 60 locations in
the contiguous United States.