Tom Kear

PM10 conformity determinations: the equivalent emissions method

Abstract The US Clean Air Act Amendments require PM10 transportation conformity and attainment demonstrations. This study examines the policy implications and validity of a proposed PM10 transportation conformity method called equivalent emissions (EE) that uses a linear, non-chemical model to incorporate emissions trading into PM10 transportation conformity determinations. We evaluate the new method by comparing predictions from EE to predictions from a mechanistic air quality model that uses non-linear chemical mechanisms to calculate the formation of secondary PM10. Results indicate that the EE method over estimates reductions of secondary PM10 formation allowing the primary fraction to rise while secondary PM10 is not actually declining in the atmosphere. Thus, conformity could be established between air quality and transportation plans using EE, resulting in projects being funded that might prolong public exposure to unhealthy levels of PM10 depending on the specifics of the non-attainment area.

A Reevaluation of Carbon Monoxide: Past Trends, Future Concentrations, and Implications for Conformity “;Hot-Spot” Policies

Abstract Control of CO is one of the great air-quality management success stories of the past 20 years. This paper evaluates whether past progress will continue into the future and whether changes in microscale CO concentrations are comparable to reductions observed at the regional scale. Neighborhood and microscale CO concentrations were evaluated at six northern and southern California monitoring sites. The study also included a review of CO emission, concentration, and exposure trends and on-road motor vehicle-based CO emission control programs for California and the United States. Consistent with California and national trends, CO concentrations declined at each of the six study locations from 1988 through 1998. Microscale concentrations declined at the same rate as did neighborhood-scale concentrations. Rollback analyses demonstrated that microscale concentrations will continue to decline through at least 2010–2020. Within a few years, microscale violations of the CO National Ambient Air Quality Standards (NAAQS) will be unlikely in California except under extraordinary circumstances.

COMPOSITE EXHAUST EMISSIONS RATES: SENSITIVITY TO VEHICLE POPULATION AND MILEAGE ACCRUAL ASSUMPTIONS

In the California Air Resources Board’s newest model of mobile-source emissions, EMFAC 2002, vehicle population and mileage accrual data have been revised such that regional vehicle miles traveled (VMT) are calculated from vehicle population and accrual data [rather than directly, using metropolitan planning organization (MPO) estimates]. Calculated VMT is forced to match the MPO VMT estimate by scaling the mileage accrual rates and altering vehicle population data. Vehicle population and mileage accrual data also determine how VMT is allocated across the vehicle model years present in the vehicle fleet; thus, modification of these data also changes the fraction of the VMT associated with each model year in the vehicle fleet. Composite emissions rates were estimated based on various vehicle population and mileage accrual data. Small perturbations in age distributions and accrual data have a larger-than-expected impact on the composite emissions rates for light-duty automobiles. For example, total organic gas emissions varied by nearly a factor of 3 between the lowest and highest estimated emissions rates, and either emissions rate could justifiably be used in an inventory. Recommendations for VMT and accrual data in subsequent release of EMFAC 2002 are provided, giving preference to the methods used by the U.S. Environmental Protection Agency.