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Gewählte Publikation:

Rieder, HE; Fiore, AM; Polvani, LM; Lamarque, JF; Fang, Y.
(2013): Changes in the frequency and return level of high ozone pollution events over the eastern United States following emission controls
ENVIRON RES LETT. 2013; 8(1), 014012 FullText FullText_BOKU

In order to quantify the impact of recent efforts to abate surface ozone (O-3) pollution, we analyze changes in the frequency and return level of summertime (JJA) high surface O-3 events over the eastern United States (US) from 1988-1998 to 1999-2009. We apply methods from extreme value theory (EVT) to maximum daily 8-hour average ozone (MDA8 O-3) observed by the Clean Air Status and Trends Network (CASTNet) and define O-3 extremes as days on which MDA8 O-3 exceeds a threshold of 75 ppb (MDA8 O-3 > 75). Over the eastern US, we find that the number of summer days with MDA8 O-3 > 75 declined on average by about a factor of two from 1988-1998 to 1999-2009. The applied generalized Pareto distribution (GPD) fits the high tail of MDA8 O-3 much better than a Gaussian distribution and enables the derivation of probabilistic return levels (describing the probability of exceeding a value x within a time window T) for high O-3 pollution events. This new approach confirms the significant decline in both frequency and magnitude of high O-3 pollution events over the eastern US during recent years reported in prior studies. Our analysis of 1-yr and 5-yr return levels at each station demonstrates the strong impact of changes in air quality regulations and subsequent control measures (e. g., the 'NOx SIP Call'), as the 5-yr return levels of the period 1999-2009 correspond roughly to the 1-yr return levels of the earlier time period (1988-1998). Regionally, the return levels dropped between 1988-1998 and 1999-2009 by about 8 ppb in the Mid-Atlantic (MA) and Great Lakes (GL) regions, while the strongest decline, about 13 ppb, is observed in the Northeast (NE) region. Nearly all stations (21 out of 23) have 1-yr return levels well below 100 ppb and 5-yr return levels well below 110 ppb in 1999-2009. Decreases in eastern US O-3 pollution are largest after full implementation of the nitrogen oxide (NOx) reductions under the 'NOx SIP Call'. We conclude that the application of EVT methods provides a useful approach for quantifying return levels of high O-3 pollution in probabilistic terms, which may help to guide long-term air quality planning.
Autor*innen der BOKU Wien:
Rieder Harald

Find related publications in this database (Keywords)
air pollution
air quality
United States
extreme value theory

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