Co-occurrence of extremes in surface ozone, particulate matter, and temperature over eastern North America

Abstract

Heat waves and air pollution episodes pose a serious threat to human health and may worsen under future climate change. In this paper, we use 15 years (1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013) of commensurately gridded (1°x 1°) surface observations of extended summer (April-September) surface ozone (O 3 ), fine particulate matter (PM 2.5 ), and maximum temperature (TX) over the eastern United States and Canada to construct a climatology of the coincidence, overlap, and lag in space and time of their extremes. Extremes of each quantity are defined climatologically at each grid cell as the 50 d with the highest values in three 5-y windows (∼95th percentile). Any two extremes occur on the same day in the same grid cell more than 50% of the time in the northeastern United States, but on a domain average, co-occurrence is approximately 30%. Although not exactly co-occurring, many of these extremes show connectedness with consistent offsets in space and in time, which often defy traditional mechanistic explanations. All three extremes occur primarily in large-scale, multiday, spatially connected episodes with scales of >1,000 km and clearly coincide with large-scale meteorological features. The largest, longest-lived episodes have the highest incidence of co-occurrence and contain extreme values well above their local 95th percentile threshold, by +7 ppb for O 3 , +6 μg m −3 for PM 2.5 , and +1.7°C for TX. Our results demonstrate the need to evaluate these extremes as synergistic costressors to accurately quantify their impacts on human health.extremes | ozone | particulate matter | heat waves

Extremal Dependence between Temperature and Ozone over the Continental U.S.

“…They also find a secondary maximum of less amplitude in the joint occurrence of extremes over the Southeastern US consistent with our analysis. However, Schnell and Prather (2017) do not find the spine of low co-occurrences clearly seen 30 in the CASTNET data from northern Alabama to Pennsylvania in our analysis. Zhang et al (2017) find the co-occurrence of extreme ozone and temperature occurs 32% of the time averaged over the U.S. with a maximum over the Northeastern U.S.…”

“…7a, b). Schnell and Prather (2017) find the co-occurence of temperature and ozone extremes also maximize over the Northeast US.…”

“…Our measurement analysis is in qualitative agreement with Schnell 25 and Prather (2017) but due to the different methodologies the quantitative results are not strictly comparable. Schnell and Prather (2017) also find that the co-occurrence of temperature and ozone extremes maximize over the Northeast US (occurring 50% or more of the time in their analysis) but decrease towards the Midwest (where joint occurrences occur 25% or less of the time). They also find a secondary maximum of less amplitude in the joint occurrence of extremes over the Southeastern US consistent with our analysis.…”

“…Sun et al (2017), calculated the conditional probability of a high ozone day (ozone above the 90th percentile) given a high temperature day (temperature above the 90th percentile). They found probabilities that ranged from approximately 50% in the northeastern U.S. to somewhat less than 20% in the western U.S. Schnell and Prather (2017) and Zhang et al (2017), calculated the joint probability that ozone and temperature are high (above the 95th percentile) compared to the probability that either one of them is high. Our measurement analysis is in qualitative agreement with Schnell 25 and Prather (2017) but due to the different methodologies the quantitative results are not strictly comparable.…”

Maximizing Ozone Signals Among Chemical, Meteorological, and Climatological Variability

“…Since ozone is strongly influenced by natural 130 fluctuations in meteorology (Jacob and Winner, 2009;Jhun et al, 2015) and since extremes in 131 surface ozone and temperature tend to co-occur (Schnell and Prather, 2017), atypically hot or 132 cold periods can strongly influence ozone behavior over short time scales. 133…”