Environmental Engineering Reference
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We further utilize OMI observations in order to test current emissions estimates
used for guiding policy initiatives in California. CARB's emissions inventory
divides emissions into source type but includes no day-of-week dependence on
emissions. Harley et al. have shown, however, that there is a strong day of week
dependence on mobile source emissions with diesel activity being largely confined
to weekdays (2005). We use traffic activity data from the EMission FACtors
(EMFAC) model, off-road activity data from the NONROAD model (Janssen,
1999) and on-road activity data from Chinken et al. (2002) to compare observations
of the weekend effect with current emission inventory estimates.
Figure 4 shows the resultant ratio of weekday to weekend NO 2 concentrations
from OMI, CARB monitoring sites, and CARB emission estimates for the three
regions of interest. For all three cases, a positive slope (South Coast = +0.07, San
Francisco = +0.04; San Joaquin Valley = +0.01) indicates that OMI is capturing
the increasing relative importance of weekday diesel NO x emissions. There is
excellent agreement between OMI tropospheric NO 2 columns and CARB surface
measurements, particularly in summers. In the South Coast region, the California
Air Resources Board's emission inventory agrees well with OMI and surface
measurements. In the San Francisco Bay and San Joaquin Valley regions, however,
emissions estimates are inconsistent with observations. This disagreement indicates
that there exists some error either in the quantitative estimate of the emissions or
in our understanding of how they vary with day of week.
Acknowledgments This work was supported by NASA (grant NNX08AE566) and CARB
(grant 06-328).
References
Bucsela EJ, Celarier EA, Wenig MO, Gleason JF, Veefkind JP, Boersma KF, Brinksma EJ
(2006) Algorithm for NO2 vertical column retrieval from the ozone monitoring instrument.
IEEE Transactions on Geoscience and Remote Sensing 44:1245-1258.
Chinkin LR, Coe DL, Funk TH, Hafner HR, Roberts PT, Ryan PA (2003) Weekday versus
weekend activity patterns for ozone precursor emissions in California's South Coast air basin.
Air & Waste Manage. Assoc. 53:829-843.
Harley RA, Marr LC, Lehner JK, Giddings SN (2005) Changes in motor vehicle emissions on
diurnal to decadal time scales and effects on atmospheric composition. Environ. Sci. Technol.
39:5356-5362.
Janssen et al. (1999) Weekday and weekend day temporal allocation of activity in the
NONROAD model. Report prepared for the U.S. Environmental Protection Agency, Office
of Mobile Sources by Nonroad Engine Emission Modeling Team, NR-015.
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