Changes in the photochemical environment of the temperate North Pacific troposphere in response to increased Asian emissions

Abstract

[1] Measurements during the Intercontinental Transport and Chemical Transformation 2002 (ITCT 2K2) field study characterized the springtime, eastern Pacific ozone distribution at two ground sites, from the National Oceanic and Atmospheric Administration WP-3D aircraft, and from a light aircraft operated by the University of Washington. D. Jaffe and colleagues compared the 2002 ozone distribution with measurements made in the region over the two previous decades and show that average ozone levels over the eastern midlatitude Pacific have systematically increased by $10 ppbv in the last two decades. Here we provide substantial evidence that a marked change in the photochemical environment in the springtime troposphere of the North Pacific is responsible for this increased O 3 . This change is evidenced in the eastern North Pacific ITCT 2K2 study region by (1) larger increases in the minimum observed ozone levels compared to more modest increases in the maximum levels, (2) increased peroxyacetyl nitrate (PAN) levels that parallel trends in NO x emissions, and (3) decreased efficiency of photochemical O 3 destruction, i.e., less negative O 3 photochemical tendency (or net rate of O 3 photochemical production; P(O 3 )). This changed photochemical environment is hypothesized to be due to anthropogenic emissions from Asia, which are believed to have substantially increased over the two decades preceding the study. We propose that their influence has changed the springtime Pacific tropospheric photochemistry from predominately ozone destroying to more nearly ozone producing. However, chemical transport model calculations indicate the possible influence of a confounding factor; unusual transport of tropical air to the western North Pacific during one early field study may have played a role in this apparent change in the photochemistry.

Increasing ozone in marine boundary layer inflow at the west coasts of North America and Europe

“…The focus of this paper is on all of west coast, North American MBL data that have been collected with the Oltmans et al (2006Oltmans et al ( , 2008 that the previously derived trends do not represent the marine troposphere. We find results here that are fully consistent with the conclusions presented by Jaffe et al (2003) and Parrish et al (2004a), with the statistical confidence considerably improved. It is shown that the data sets on which Oltmans et al (2006Oltmans et al ( , 2008 based their suggestions have serious shortcomings.…”

“…Investigators have presented evidence that the background O 3 has increased since the mid-1980s at northern mid latitudes in air entering both the North American west coast form the North Pacific Ocean (Jaffe et al, 2003;Parrish et al, 2004a) and the European west coast from the North Atlantic Ocean (Simmonds et al, 2004;Derwent et al, 2007). Parrish et al (2004a) argue that the increase in the North Pacific has occurred in response to increasing Asian emissions of O 3 precursors, which are transported to the North Pacific troposphere.…”

“…Parrish et al (2004a) argue that the increase in the North Pacific has occurred in response to increasing Asian emissions of O 3 precursors, which are transported to the North Pacific troposphere. However, other investigators (Oltmans et al, 2006(Oltmans et al, , 2008 have suggested that the reported increase at the North American west coast was actually caused by local North American continental effects rather than representing an increase in the background marine O 3 .…”

“…Jaffe et al (2003) and Parrish et al (2004a) presented trend determinations based on three different data sets: first, several relatively short-term measurement records from different MBL sites that spanned 18 years; second, one continuous 15-year record from Lassen Volcanic National Park; and third, two aircraft campaigns conducted over the eastern North Pacific 18 years apart. All three of the derived trends are consistent with each other and indicate a springtime (the season of the focus of those studies) increase of 0.5 ppbv/yr.…”

Free tropospheric peroxyacetyl nitrate (PAN) and ozone at Mount Bachelor: potential causes of variability and timescale for trend detection

“…There are multiple lines of evidence that springtime O 3 concentrations are increasing over western North America Chan and Vet, 2010;Parrish et al, 2009;Jaffe et al, 2003;Jaffe and Ray, 2007;NRC, 2010;Parrish et al, 2004). The most recent analysis by Cooper et al (2010) showed a strong increase in lower free tropospheric (FT) springtime O 3 mixing ratios from 1995 to 2008.…”