Increasing background ozone during spring on the west coast of North America

Abstract

Using a 15‐year record of O3 from Lassen Volcanic National Park, a rural elevated site in northern California, data from two aircraft campaigns conducted in 1984 and 2002 over the eastern North Pacific, and observations spanning 18 years from five U.S. west coast, marine boundary layer sites, we show that O3 in air arriving from the Eastern Pacific in spring has increased by approximately 10 ppbv, i.e. 30% from the mid 1980s to the present. This positive trend in O3 correlates with the increasing trend in global nitrogen oxide emissions, which is especially pronounced in Asia. As spring is the season of strongest transport of Asian emissions to the Pacific, we conclude that the emission trend is the most likely cause of the O3 trend.

Surface ozone concentrations and ecosystem health: Past trends and a guide to future projections

“…The 'background' seasonal cycle at Arosa was very similar to that at Mace Head, suggesting a regional scale pattern of concentration in unpolluted air. Similar trends to those reported for western Europe are seen at the west coast of North America, where 7 out of 9 sites showed an average O 3 increase between 1987 and 2004 of 0.26 ppb y -1 (Jaffe et al, 2003;Jaffe and Ray, 2007). No trends could be seen in vertical profiles from ozonesonde measurements, but this was attributed to the variability in the data set caused by irregular sampling intervals.…”

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

“…The earliest O 3 data from 1985 were collected by one of the groups involved in the 2002 study. We are confident that systematic errors in the O 3 measurements make negligible contributions to the temporal trend reported by Jaffe et al [2003]. The precision of the data points used here is within ±2% or 1 ppbv, whichever is greater.…”

“…Consequently, we will investigate the relationships between measured concentrations of different species through logarithmic plots and perform linear, least squares fits to log transformed concentrations. [15] Figure 3 shows the coastal marine O 3 measurements discussed by Jaffe et al [2003], who concluded that the O 3 levels in air arriving at the U.S. West Coast have increased by about 30% over the past two decades. This increase is evident in the slopes of the temporal trend lines in Figure 3, which are summarized in Table 2.…”

“…In eastern Asia, nitrogen oxides (NO x ) emissions grew by approximately 5.6%/yr between 1985 and 1997, but since that time have leveled off and may have even dropped [Streets et al, 2003]. Jaffe et al [2003] suggest that the increased NO x emissions in the upwind Asian continent are likely responsible for the increased O 3 levels in North Pacific air masses reaching North America. In this paper we examine the few data sets that have been collected in the North Pacific region in spring over the last two decades to elucidate how increased Asian NO x emissions may have influenced the photochemical environment of the North Pacific troposphere leading to the increased O 3 levels.…”

Interactions of forests with secondary air pollutants: Some challenges for future research

“…'Acid rain' and ozone are the most studied secondary pollutants, as far as forest effects are concerned, and while amounts of wet-deposited acidity (and sulphate and nitrate) have decreased, there are still large areas of Europe and North America that exceed the Critical Loads for forests (Hettelingh et al, 1995). Moreover, the increasing industrialisation of India, China and south-east Asia is leading to a gradual increase in the 'background' concentrations of ozone across the northern hemisphere, with several studies demonstrating that long-range (intercontinental) transport of ozone and/or its precursors is affecting annual average ozone concentrations across the whole hemisphere (Auvray and Bey, 2005, Derwent et al, 2006, Jaffe et al, 2003, Jonson et al, 2006, Oltmans et al, 2006, Vingarzan, 2004. This gradual increase in 'background' ozone is set against a pattern of decreasing severity of peak ozone concentrations during episodes, which can be attributed to the effects of emission controls, particularly on VOCs (Derwent et al, 2003).…”