Formation of photochemical air pollution in central California 2. Impact of revised emissions on Eulerian model predictions

Abstract

Attempts to characterize ozone formation as sensitive to either volatile organic compounds (VOC) or NOx within a region oversimplify a problem that shows spatial and temporal variation. California's Central Valley has some of the highest ozone levels in the country and a rapidly growing population, and air quality problems in this region can be influenced by interbasin transport of ozone and its precursors. An Eulerian photochemical airshed model is applied to the region for the period 3–6 August 1990. This episode spans a weekend, and the emission inventory incorporates revised motor vehicle emissions with day‐specific activity patterns. Compared with the baseline inventory, the revised inventory contains higher VOC and lower NOx emissions from motor vehicles and different temporal patterns of these emissions. Revised estimates of biogenic emissions are greatly reduced. The baseline emission inventory used in previous modeling efforts appears to contain compensating errors, with high biogenic emissions making up for low motor vehicle emissions of VOC. Results suggest that heavily urbanized areas around and downwind of the San Francisco Bay and Sacramento are VOC‐sensitive, while the more rural areas are NOx‐sensitive. Ozone formation in the San Joaquin Valley, where progress in reducing ambient ozone concentrations has been slow, exhibits sensitivity to emissions of both VOC and NOx, and is influenced by emissions from the San Francisco Bay Area during this modeling episode.

Modeling ozone photochemistry and evaluation of hydrocarbon emissions in the Mexico City metropolitan area

“…In this study, we use a three‐dimensional Eulerian photochemical airshed model called the California Institute of Technology (CIT) airshed model [ McRae et al , 1982]. The CIT model has been applied and tested extensively in the past in urban regions [ McRae et al , 1982; Russell et al , 1988; Milford et al , 1989; Harley et al , 1993, 1997; Kuebler et al , 1996; Ulke and Andrade , 2001; Marr et al , 2002], and was previously applied to Mexico City during the MARI project [ LANL and IMP , 1994; Streit and Guzmán , 1996]. The version of CIT used in this study includes the SAPRC99 chemical mechanism [ Carter , 2000], which is among the most recent chemical mechanisms available.…”

Modeling the Effect of Weekday−Weekend Differences in Motor Vehicle Emissions on Photochemical Air Pollution in Central California

“…During the last two days of the episode, meteorological conditions were especially favorable for ozone formation, with higher than normal temperatures; ambient ozone concentrations as high as 160 ppb were measured on 6 August. Marr et al (27) described in detail the modeling system and evaluation of its performance in predicting ozone and precursor concentrations for this episode. Revision of the original motor vehicle and biogenic emission inventories, which appeared to contain compensating errors in VOC, resulted in improved ozone and VOC predictions and an increase in model bias for NOx and its oxidation products (NOy).…”

Mobile laboratory measurements of black carbon, polycyclic aromatic hydrocarbons and other vehicle emissions in Mexico City

“…Remote sensing and tunnel studies have reported light-duty NO x emission factors of 7 g kg −1 in the US in recent years (Harley et al, 2005;Pokharel et al, 2002). The average heavy-duty NO x emission factor in the US is 39 g kg −1 (Marr et al, 2002) and has not changed significantly over the past 20 years (Yanowitz et al, 2000). Mexico City's combined NO x emission factor of 19 g kg −1 falls in between light-and heavy-duty 20 values found in the US.…”