Response of regional and urban air quality to global climate change

In the United States, the effects of changes in climate on air quality are not considered in air pollutant emissions policy. However, changes in climate over the next several decades may have important effects on pollutant concentrations. This work focuses on the effects of changes in climate on air quality. The effects on concentrations of ozone (O3) and fine particulate matter (PM2.5) are considered.; The sensitivities of ozone concentrations to perturbations in a base case meteorology were investigated in a modeling study over the Eastern US using the chemical transport model PMCAMx. Base case meteorology from 12-21 July 2001 was perturbed one meteorological variable at a time so the sensitivity of ozone to individual meteorological parameters could be determined. The meteorological parameters investigated included temperature, wind speed, absolute humidity, mixing height, cloud cover, and precipitation. The meteorological factor that had the largest impact on both ozone metrics was temperature, which increased daily maximum 8-hour average O3 by 0.34 ppb K -1 on average over the simulation domain. Temperature also had the strongest effect on exceedances of the 8-hour ozone air quality standard. Wind speed and mixing height also had appreciable effects on ozone concentrations.; The same methodology was used to investigate the sensitivity of PM 2.5 concentrations to individual meteorological parameters. This study used base case meteorology from 12-21 July 2001 and 6-15 January 2002. Temperature had a major effect on average PM2.5 in January (-170 ng m -3 K-1) due largely to the evaporation of ammonium nitrate and organic aerosol at higher temperatures; increases in sulfate production with increased temperature counteracted much of this decrease in July. Changes in mixing height, wind speed, and precipitation also had appreciable effects on PM2.5 concentrations.; A new modeling system was developed in order to investigate the effects of global climate change and pollutant transport on regional air quality. The Global-REgional Climate-Air Pollution modeling System (GRE-CAPS) consists of a general circulation model/chemical transport model (GCM/CTM) at the global scale, a regional meteorological model for downscaling global meteorology, and the PMCAMx regional chemical transport model. Transport into the eastern US is simulated using boundary conditions that were calculated by the GCM/CTM around the edge of the eastern US. GRE-CAPS is shown to agree rather well with measurements of O3 and speciated PM2.5 around the eastern US. The biases and errors for GRE-CAPS were similar to those of PMCAMx when used for standard retrospective episode modeling.; GRE-CAPS was used to simulate air quality under GCM-predicted present-day and 2050s climate and constant (present-day) emissions. Average concentrations of July ozone increased by 0.7 ppb, with the largest increases over the Southeast. Average exceedances of the 8-hour ozone air quality standard, however, decreased under the future climate. Average concentrations of PM2.5 in January decreased by 0.6 mug m-3, due largely to increases in precipitation. Average concentrations of PM2.5 in July increased by 2.2 mug m-3, with concentrations of sulfate increasing the most of any species. The increase in July PM2.5 was due mainly to increased temperature and decreased wind speed and mixing height.; The effect of climate change under reduced- and increased-precursor emissions scenarios was investigated using GRE-CAPS. Generally, climate had smaller effects on July O3 and PM2.5 concentrations under reduced emissions and larger effects under larger emissions. Changes in emissions were also predicted to have a larger impact on air quality under the future climate than under the present climate.; The results of these studies suggest that climate will have important effects on air pollution over the next several decades. These studies also suggest that the effects of climate on air quality are depe...