DOI: 10.5061/dryad.nk98sf7z2
title: Data for: Projecting changes in the frequency and magnitude of ozone pollution events under uncertain climate sensitivity

description: Climate change is projected to worsen ozone pollution over many populated
 regions, with larger impacts at higher concentrations. More intense and
 frequent ozone episodes risk setbacks to human health and environmental
 policy achievements. However, assessing these changes is complicated by
 uncertain climate sensitivity, closely related to climate model response,
 and internal variability in simulations projecting climate’s influence on
 air quality. Here, leveraging a global modeling framework that one-way
 couples a human activity model, an Earth system model of intermediate
 complexity, and an atmospheric chemistry model, we investigate the role of
 climate sensitivity in climate-induced changes to high ozone pollution
 episodes in the United States using multiple greenhouse gas emissions
 scenarios, representations of climate sensitivity, and initial condition
 members. We bias correct and evaluate historical model simulations,
 identifying modeled and observed O3 episodes using extreme value theory,
 and extend the approach to projections of mid- and end-century climate
 impacts. Results show that the influence of climate sensitivity can be as
 significant as that of greenhouse gas emissions scenario absent precursor
 emissions changes. Climate change is projected to increase the magnitude
 of the highest annually occurring O3 concentrations by over 2.3 ppb on
 average across the U.S. at mid-century under a high climate sensitivity
 and moderate emissions scenario, but the increase is limited to less than
 0.3 ppb under lower climate sensitivity. Further, we show that areas in
 the U.S. currently meeting air quality standards risk being pushed into
 non-compliance due to a climate-induced increase in frequency of high
 ozone days.
description: # README for Projecting changes in the frequency and magnitude of ozone
 pollution events under uncertain climate sensitivity --- Contact:
 [f_garcia@ncsu.edu](mailto:f_garcia@ncsu.edu) Data included in this folder
 are described below ## Description of the data and file structure ###
 GRIDDED DATA Files are provided in NetCDF format on a global grid, with
 data masked outside the U.S. The following types of data are included: *
 Bias-corrected MDA8 ozone concentrations (folder camchem_adj) * Annual
 files of daily MDA8 ozone-season concentrations are included for each
 available climate sensitivity, emissions scenario, and initial condition
 ensemble member at beginning, middle, and end-century. Each file contains
 153 days of gridded ozone-season bias-corrected concentrations. * File
 name convention: POL.CS.IC.YYYY-YYYY.yyyy.AQ.nc where POL is the emissions
 scenario (REF, P45, or P37), CS is the climate sensitivity scenario (CS45,
 CS30, CS20), YYYY-YYYY is the time span indicating beginning, middle, or
 end-century (1981-2010, 2036-2065, 2086-2115), and yyyy is the specific
 year for that file. * Ozone 1-year return levels (folder retvals) *
 Probabilistic 1-year return levels are included for each available climate
 sensitivity, emissions scenario, and initial condition ensemble member at
 beginning, middle, and end-century. Each file contains gridded 1-year
 ozone return level (units of ppb) and gridded values for
 Kolmogorov-Smirnov (K-S) test results. * File name convention:
 POL.CS.IC.YYYY-YYYY.O3X.1YR.nc where POL is the emissions scenario (REF,
 P45, or P37), CS is the climate sensitivity scenario (CS45, CS30, CS20),
 and YYYY-YYYY is the time span indicating beginning, middle, or
 end-century (1981-2010, 2036-2065, 2086-2115). * Ozone 70-ppb return
 intervals (folder retperiods) * Probabilistic return intervals for 70-ppb
 MDA8 ozone are included for each available climate sensitivity, emissions
 scenario, and initial condition ensemble member at beginning, middle, and
 end-century. Each file contains gridded 1-year ozone return level (units
 of ppb) and gridded values for Kolmogorov-Smirnov (K-S) test results. *
 File name convention: POL.CS.IC.YYYY-YYYY.O3X.1YR.nc where POL is the
 emissions scenario (REF, P45, or P37), CS is the climate sensitivity
 scenario (CS45, CS30, CS20), and YYYY-YYYY is the time span indicating
 beginning, middle, or end-century (1981-2010, 2036-2065, 2086-2115). ###
 RETURN VALUES * Probabilistic return values calculated from observed and
 modeled concentrations at CASTNET sites (folder return_values_at_sites) *
 CSV files for 1, 2, 5, 10, 25-year return values at CASTNET sites and for
 each IC member in the historical simulation. Data columns included are
 site (CASTNET site code), return period (units of years), return value
 (units of ppb), lower ci (return value confidence interval lower bound,
 units of ppb), upper ci (return value confidence interval upper bound,
 units of ppb), nextremes (count of MDA8 ozone exceedances of 70 ppb
 threshold) * Probabilistic return values calculated from observed and
 modeled concentrations at CASTNET sites, for the Pre-SIP period only
 (folder return_values_at_sites_preSIP) * CSV files for 1, 2, 5, 10,
 25-year return values at CASTNET sites and for each IC member in the
 historical simulation. Data columns included are site (CASTNET site code),
 return period (units of years), return value (units of ppb), lower ci
 (return value confidence interval lower bound, units of ppb), upper ci
 (return value confidence interval upper bound, units of ppb), nextremes
 (count of MDA8 ozone exceedances of 70 ppb threshold) * Probabilistic
 return values calculated from observed and modeled concentrations at
 CASTNET sites, for the uncorrected model concentrations (folder
 return_values_at_sites_uncorrected) * CSV files for 1, 2, 5, 10, 25-year
 return values at CASTNET sites and for each IC member in the historical
 simulation. Data columns included are site (CASTNET site code), return
 period (units of years), return value (units of ppb), lower ci (return
 value confidence interval lower bound, units of ppb), upper ci (return
 value confidence interval upper bound, units of ppb), nextremes (count of
 MDA8 ozone exceedances of 70 ppb threshold) * Null values
 ("NaN") in the return value csv datasets mean the specified
 return value at that site cannot be calculated because there are too few
 values above the exceedance threshold of 70ppb. ## Sharing/Access
 information ### CASTNET data CASTNET data used in this study are publicly
 available from the U.S. Environmental Protection Agency at
 [https://www.epa.gov/castnet](https://www.epa.gov/castnet)