The influence of foreign vs. North American emissions on surface ozone in the US

D R Reidmiller,D T Shindell,A Lupu,B N Duncan,A Zuber,D Bergmann,R Park,Terry Keating ,Peter Hess ,Cornelis Cuvelier ,Sophie Szopa ,Elina Marmer ,Frank Dentener ,Oliver Wild ,Marta G Vivanco ,Arlene M Fiore ,Jan Eiof Jonson ,Sunling Gong ,Gerd Folberth ,Michael Gauss ,Daniel A Jaffe ,Martin Schultz

doi:10.5194/acp-9-5027-2009

Abstract

Abstract. As part of the Hemispheric Transport of Air Pollution (HTAP; http:// www.htap.org) project, we analyze results from 15 global and 1 hemispheric chemical transport models and compare these to Clean Air Status and Trends Network (CASTNet) observations in the United States (US) for 2001. Using the policy-relevant maximum daily 8-h average ozone (MDA8 O3) statistic, the multi-model ensemble represents the observations well (mean r2=0.57, ensemble bias = +4.1 ppbv for all US regions and all seasons) despite a wide range in the individual model results. Correlations are strongest in the northeastern US during spring and fall (r2=0.68); and weakest in the midwestern US in summer (r2=0.46). However, large positive mean biases exist during summer for all eastern US regions, ranging from 10–20 ppbv, and a smaller negative bias is present in the western US during spring (~3 ppbv). In nearly all other regions and seasons, the biases of the model ensemble simulations are ≤5 ppbv. Sensitivity simulations in which anthropogenic O3-precursor emissions (NOx + NMVOC + CO + aerosols) were decreased by 20% in four source regions: East Asia (EA), South Asia (SA), Europe (EU) and North America (NA) show that the greatest response of MDA8 O3 to the summed foreign emissions reductions occurs during spring in the West (0.9 ppbv reduction due to 20% emissions reductions from EA + SA + EU). East Asia is the largest contributor to MDA8 O3 at all ranges of the O3 distribution for most regions (typically ~0.45 ppbv) followed closely by Europe. The exception is in the northeastern US where emissions reductions in EU had a slightly greater influence than EA emissions, particularly in the middle of the MDA8 O3 distribution (response of ~0.35 ppbv between 35–55 ppbv). EA and EU influences are both far greater (about 4x) than that from SA in all regions and seasons. In all regions and seasons O3-precursor emissions reductions of 20% in the NA source region decrease MDA8 O3 the most – by a factor of 2 to nearly 10 relative to foreign emissions reductions. The O3 response to anthropogenic NA emissions is greatest in the eastern US during summer at the high end of the O3 distribution (5–6 ppbv for 20% reductions). While the impact of foreign emissions on surface O3 in the US is not negligible – and is of increasing concern given the recent growth in Asian emissions – domestic emissions reductions remain a far more effective means of decreasing MDA8 O3 values, particularly those above 75 ppb (the current US standard).

Highlights

We present multi-model results from the Hemispheric Transport of Air Pollution (HTAP) experiments which reduced anthropogenic O3-precursor emissions by 20% in four northern hemispheric source regions
We began by developing a novel method to determine “regionally-representative” sites to which the multi-model results were compared (Figs. 2 and A1)
We provided context for the year of the HTAP simulations (2001) by comparing with 17 years of Clean Air Status and Trends Network (CASTNet) data (Figs. 3 and A2)

Summary

Introduction

It is well-established that the intercontinental transport of pollutant emissions affects surface air quality in the United States (Berntsen et al, 1999; Jacob et al, 1999; Jaffe et al, 1999; Fiore et al, 2002; Goldstein et al, 2004; Keating et al, 2005; Sudo and Akimoto, 2007; Lin et al, 2008; Oltmans et al, 2008; Zhang et al, 2008; Fischer et al, 2009). Over the past 15 years, a multitude of field campaigns have attempted to quantify the effect of Asian emissions on US air quality and how these emissions are affecting the photochemical environment over the North Pacific. The Transport and Chemical Evolution over the Pacific (TRACE-P; Jacob et al, 2003) and Intercontinental Transport and Chemical Transformation (ITCT 2K2; Parrish et al, 2004a; Goldstein et al, 2004) campaigns were conducted during spring - the season of greatest East Asian transport to North America – of 2001 and 2002, respectively. In spring 2006, the Intercontinental Chemical Transport Experiment (INTEX-B; Singh et al, 2009) was a coordinated satellite, aircraft and ground-based campaign designed in large part to quantify the import of Asian pollutants to western North America. Satellite data are being used to better understand and quantify the intercontinental transport of pollutants (Heald et al, 2003; Damoah et al, 2004; Creilson et al, 2003; Wenig et al, 2003)

Objectives

Methods

Findings

Conclusion