title: 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 (1999-2013) of commensurately gridded (1° x 1°) surface observations of extended summer (April-September) surface ozone (O3), fine particulate matter (PM2.5), 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 O3, +6 µg m-3for PM2.5, 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.
authors.affiliation: Department of Earth System Science, University of California, Irvine, CA 92697 jordan.schnell@princeton.edu.
authors.forename: Jordan L
authors.initials: JL
authors.lastname: Schnell
authors.affiliation: Department of Earth System Science, University of California, Irvine, CA 92697.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Prather
mesh_terms: D000397:Air Pollution / Q000009:adverse effects*; D002170:Canada; D057231:Climate Change; D004784:Environmental Monitoring; D006801:Humans; D007259:Infrared Rays / Q000009:adverse effects*; D009511:New England; D009656:North America; D010126:Ozone / Q000009:adverse effects / Q000302:isolation & purification; D052638:Particulate Matter / Q000009:adverse effects; D012621:Seasons; D013696:Temperature
chemical_list: D052638:Particulate Matter; D010126:Ozone
keywords: extremes; heat waves; ozone; particulate matter