Sensitivity of PM_2.5 to climate in the Eastern US: a modeling case study

Abstract. The individual effects of various meteorological parameters on PM_2.5 concentrations in the Eastern US are examined using the PMCAMx chemical transport model so that these effects and their relative magnitudes can be better understood. A suite of perturbations in temperature, wind speed, absolute humidity, mixing height, cloud cover, and precipitation are imposed individually on base case conditions corresponding to periods in July 2001 and January 2002 in order to determine the sensitivities of PM_2.5 concentrations and composition to these separate meteorological parameters. Temperature had a major effect on average PM_2.5 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 also had major effects on PM_2.5 concentrations: 73 ng m⁻³ (100 m)⁻¹ in January and 210 ng m⁻³ (100 m)⁻¹ in July. Changes in wind speed (30 to 55 ng m⁻³ %⁻¹) and absolute humidity (15 to 20 ng m⁻³ %⁻¹) also had appreciable effects on average PM_2.5 concentrations. Precipitation changes had large impacts on parts of the domain (a consequence of the base case meteorology), with sensitivities to changing area of precipitation in July up to 100 ng m⁻³ %⁻¹. Perturbations in cloud cover had the smallest effects on average PM_2.5 concentrations. The changes in PM_2.5 concentrations resulting from changing all eight meteorological parameters simultaneously were approximately within 25% or so of the sum of the changes to the eight individual perturbations. The sensitivities of PM_2.5 concentrations to changes in these meteorological parameters indicate that changes in climate could potentially have important impacts on PM_2.5 concentrations.