Environmental Engineering Reference
In-Depth Information
We use the OMI standard product from October 2004 to August 2008 (Bucsela,
2006). Data chosen for analysis has been filtered to exclude pixels with a cloud
fraction exceeding 0.2. We take advantage of OMI's 16-day repeat pattern and use
an area-weighted averaging, binning to a 0.025° × 0.025° grid. In
Fig. 1a
we show
summer concentration over 3 years. In
Fig. 2 w
e show average weekday and
weekend concentrations of NO
2
across California for summers 2005-2008. Both
panels show elevated concentrations of NO
2
in and around highly populated areas.
We compare OMI tropospheric column concentrations with observations from
a network of ground monitoring sites maintained by the California Air Resources
Board (CARB). We focus on summer observations because the NO
2
lifetime is
shorter in the summer so we can expect the column to be more representative of
surface emissions on that day.
Figure 3
shows the average day of week patterns
observed by OMI and the CARB sites for three regions of interest; the San
Francisco Bay Area, the South Coast, and the San Joaquin Valley air basins. On
average, we see Saturday and Sunday concentrations that are 27% and 40% lower
than weekday values, respectively.
(a)
(
Fig. 1.
(a) Tropospheric column NO
2
concentrations (molecules/cm
2
) from OMI over the South
Coast region of California from August 1, 2008. (b) OMI tropospheric NO
2
columns averaged
over summer months (June-August) for the years 2005-2008 at 0.025° resolution
Fig. 2.
Average OMI tropospheric NO
2
column concentrations (molecules/cm
2
) for (a) weekdays
(Tuesday-Friday) and (b) weekends (Saturday-Sunday) for June-August 2005-2008
