Abstract
Abstract. The Pacific–North America teleconnection (PNA) is the leading general circulation pattern in the troposphere over the region of North Pacific to North America during wintertime. This study examined the impacts of monthly variations of the PNA phase (positive or negative phase) on wintertime surface-layer aerosol concentrations in the United States (US) by analyzing observations during 1999–2013 from the Air Quality System of the Environmental Protection Agency (EPA-AQS) and the model results for 1986–2006 from the global three-dimensional Goddard Earth Observing System (GEOS) chemical transport model (GEOS-Chem). The composite analyses on the EPA-AQS observations over 1999–2013 showed that the average concentrations of PM2.5, sulfate, nitrate, ammonium, organic carbon, and black carbon aerosols over the US were higher in the PNA positive phases (25 % of the winter months examined, and this fraction of months had the highest positive PNA index values) than in the PNA negative phases (25 % of the winter months examined, and this fraction of months had the highest negative PNA index values) by 1.0 µg m−3 (8.7 %), 0.01 µg m−3 (0.5 %), 0.3 µg m−3 (29.1 %), 0.1 µg m−3 (11.9 %), 0.6 µg m−3 (13.5 %), and 0.2 µg m−3 (27.8 %), respectively. The simulated geographical patterns of the differences in concentrations of all aerosol species between the PNA positive and negative phases were similar to observations. Based on the GEOS-Chem simulation, the pattern correlation coefficients were calculated to show the impacts of PNA-induced variations in meteorological fields on aerosol concentrations. The PNA phase was found (i) to influence sulfate concentrations mainly through changes in planetary boundary layer height (PBLH), precipitation (PR), and temperature; (ii) to influence nitrate concentrations mainly through changes in temperature; and (iii) to influence concentrations of ammonium, organic carbon, and black carbon mainly through changes in PR and PBLH. Results from this work have important implications for the understanding and prediction of air quality in the US.
Highlights
Aerosols are the major air pollutants that have adverse effects on human health, reduce atmospheric visibility, and influence climate through aerosol–radiation and aerosol–cloud interactions (IPCC, 2013)
Simulated geographical patterns of the differences in PM2.5 and each aerosol species between the Pacific–North America teleconnection (PNA)+ and PNA− months were similar to those seen in observations in most areas of the United States (US), with the largest increases in aerosol concentrations in PNA+ months over and near the eastern Midwest
This study examined the impacts of monthly variation in the PNA phase on wintertime surface-layer aerosol concentrations in the US by the analyses of EPA-AQS observations over 1999–2013 and model results for 1986–2006 from the global chemical transport model Goddard Earth Observing System (GEOS)-Chem
Summary
Aerosols are the major air pollutants that have adverse effects on human health, reduce atmospheric visibility, and influence climate through aerosol–radiation and aerosol–cloud interactions (IPCC, 2013). Gong et al (2006) studied the interannual variations in the trans-Pacific transport of Asian dust during 1960– 2003 by using the northern aerosol regional climate model (NARCM) They found a negative correlation (with a correlation coefficient of −0.55) between the PNA and the ratio of dust mass that reached the North American continent to that exported from Asia because of the strong westerly jet in the East Pacific during the negative PNA phases. We examine in this work the impacts of monthly variations in PNA phase on aerosol concentrations in the US during wintertime, by analyses of the observed aerosol concentrations during 1999–2013 from EPA-AQS and by simulations of aerosol concentrations for years 1986–2006 using the global chemical transport model GEOS-Chem.
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