Long‐term ozone trends at rural ozone monitoring sites across the United States, 1990–2010

Abstract

[1] This analysis provides an up-to-date assessment of long-term rural ozone trends using all available data in the western (12 sites) and eastern (41 sites) USA. Rather than focus solely on average ozone values or air quality standard violations, we consider the full range of ozone values, reporting trends for the 5th, 50th and 95th percentiles. Domestic ozone precursor emissions decreased strongly during 1990-2010. Accordingly 83%, 66% and 20% of summertime eastern U.S. sites experienced statistically significant ozone decreases in the 95th, 50th and 5th percentiles, respectively. During spring 43% of the eastern sites have statistically significant ozone decreases for the 95th percentile with no sites showing a significant increase. At the 50th percentile there is little overall change in the eastern U.S. In contrast, only 17% (2 sites) and 8% (1 site) of summertime western U.S. sites have statistically significant ozone decreases in the 95th and 50th percentiles, respectively. During spring no western site has a significant decrease, while 50% have a significant median increase. This dichotomy in U.S. ozone trends is discussed in terms of changing anthropogenic and biomass burning emissions. Consideration is given to the concept that increasing baseline ozone flowing into the western U.S. is counteracting ozone reductions due to domestic emission reductions. An update to the springtime free tropospheric ozone trend above western North America shows that ozone has increased significantly from 1995 to 2011 at the rate of 0.41 AE 0.27 ppbv yr À1 . Finally, the ozone changes are examined in relation to regional temperature trends.

Modeling intercontinental transport of ozone in North America with CAMx for the Air Quality Model Evaluation International Initiative (AQMEII) Phase 3

“…In particular, high-O 3 events over the high terrain in the western US have been linked to intercontinental transport and stratospheric intrusions (Lin et al, 2012a, b). The highest modeled contributions occur in spring, which is consistent with observations (Parish et al, 2012;Cooper et al, 2012) and previous modeling studies (Emery et al, 2012;Fiore et al, 2014). BC contributions in the eastern US are generally below 40 ppb in spring and below 30 ppb in other seasons.…”

Lower tropospheric ozone at northern midlatitudes: Changing seasonal cycle

“…[15] In contrast, within Europe and North America, decreasing O 3 precursor emissions have led to reductions in peak summertime ozone concentrations at surface continental sites [Royal Society, 2008;Cooper et al, 2012]. At the same time decreasing NO x emissions have resulted in less loss of O 3 via NO titration in winter and early spring [e.g., Jonson et al, 2006], manifesting itself in positive wintertime O 3 trends at European and North American sites [e.g., Wilson et al, 2012;Parrish et al, 2012;Cooper et al, 2012].…”

Atmospheric Science Research at Whiteface Mountain, NY: Site Description and History

“…Many of these locations, including Whiteface, have decades and more of history and scientific observations. The long term data sets produced at these mountain sites are a cultural and scientific resource of great value for many types of research (HEI, 2003;Cooper et al, 2012). For example, there is an increasing interest in climatic and ecological research at the world's mountain sites as the scientific community works to understand the many implications of climate change.…”