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UPDATED PHOTOCHEMICAL MODELING FOR CALIFORNIA'S SOUTH COAST AIR BASIN: COMPARISON OF CHEMICAL MECHANISMS AND MOTOR VEHICLE EMISSION INVENTORIES. (R824792)
Citation:
Harley, R. A., R. F. Sawyer, AND J. B. Milford. UPDATED PHOTOCHEMICAL MODELING FOR CALIFORNIA'S SOUTH COAST AIR BASIN: COMPARISON OF CHEMICAL MECHANISMS AND MOTOR VEHICLE EMISSION INVENTORIES. (R824792). ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 31(10):2829-2839, (1997).
Description:
Large uncertainties remain in photochemical models used
to relate emissions of VOC and NOx to ambient
O3
concentrations. Bias in motor vehicle emission
estimates
for VOC has been a long-standing concern. An improved
Eulerian photochemical model is described and applied to
the August 27-28, 1987, period in southern California.
The chemical mechanism used in the model is SAPRC93,
which predicts peak ozone concentrations 22% higher
on average than the LCC mechanism used previously. A
revised motor vehicle emission inventory was developed
using gasoline sales and infrared remote sensing data for
CO and measured ambient NMOC/CO and NOx/CO
ratios.
On-road vehicle emissions for the South Coast Air Basin
in
summer 1987 were estimated to be (1800 ± 400) ×
103
and (710 ± 160) × 103 kg
day-1 for NMOC and
NOx, respectively.
These values are 2.4 and 1.0 times, respectively, the
cor
responding current official inventory estimates (MVEI 7G).
Ozone concentrations predicted using the CIT airshed
model matched observations more closely when the revised
inventory was used in place of official emission
estimates.
If the vehicle fleet in 1987 were operating with no
emission controls, NMOC and NOx emissions would
have
been 5900 × 103 and 1200 × 103 kg
day-1 respectively.
On average, peak predicted ozone concentrations for
the
controlled vehicle fleet operating in 1987 were 43% lower
than values predicted for the uncontrolled vehicle fleet.
The
peak predicted ozone concentration with the uncontrolled
vehicle fleet was 500 ppb.