Climate Change Impacts on Regional Air Quality Loretta Mickley and co-workers: Shiliang Wu, Eric Liebensperger, Dominick Spracklen, Cynthia Lin, Daniel Jacob, David Rind, David Streets Views of London smog episode, 5-9 December 1952: result of cold stagnant air + coal combustion

Day-to-day weather plays a large role in surface air quality. Stalled high pressure system leads to high surface ozone levels due to combined effects of increased biogenic emissions, clear skies, weak winds, & high temperatures. cold front EPA ozone levels 3 days later Cold front pushes smog poleward and aloft on a warm conveyor belt. cold front Unhealthy for “sensitive people”, including joggers, cyclists... L L

Probability of ozone exceedance vs. daily max. temperature Will future emissions reductions swamp effects of climate change on US air quality? (40% decrease in NOx emissions in A1B by 2050). Northeast The total derivative d[O 3 ]/dT is the sum of partial derivatives (  O 3 /  x i )(  x i /  T), where x is the ensemble of ozone forcing variables that are temperature-related. 1988, hottest on record Average num. of days Number of summer days with 8-hour average ozone > 84 ppbv over northeast U.S. sites Curves include effects of T-dependent biogenic emissions, stagnation, … Lin et al., 2001

Pollution episodes double in duration in 2050s due to decreasing frequency of cyclones ventilating the eastern U.S sink = constant OH sink = changing precip July - August GISS GCM simulations for 2050s vs. present-day climate using pollution tracers with constant, present-day anthropogenic emissions. Fewer cold front passages allowing pollutants to build up. Changes at extremes due to 10-20% decrease in summertime cyclogenesis. Mickley et al., 2004

A decrease in cyclone frequency across mid-latitudes has already been observed (and calculated) for recent decades. Observed trend in winter cyclone frequency over Northern Hemisphere. McCabe et al., 2001 Calculated trend in summer cyclone frequency, from GISS 2x2.5 GCM, 23 layers Climate models tend to predict decrease in mid-latitude cyclogenesis in future due to: decrease in meridional temperature gradient more efficient poleward transport of latent heat Leibensperger et al., 2007

Investigating the effect of global change on regional air quality Chemistry, transport, deposition, etc GHG Air pollutants & their precursors Climate Change GISS GCM 3 23 vertical layers extending to 85 km Horizontal resolution of 4º x 5º GEOS-Chem detailed ozone-NOx-VOC-aerosol chemistry Anthropogenic emissions (IPCC A1B scenario) Natural emissions Radiative forcing GCAP (Global Change and Air Pollution) model

Effects of global change on U.S. ozone air quality climate – emission – – 2000 Daily max 8h-avg ozone averaged over JJA (ppb) Increase of summer max- 8h-avg ozone by 1-5 ppb in large areas of U.S. due to climate change. Fewer effects in western U.S. because (1) increase of ozone from intercontinental transport and (2) anthro. emissions are low there. Wu et al., 2007

Changes in summertime air pollution meteorology due to climate change Surface temperature (2050 – 2000) Convective mass flux ( ) Mixing depth (2050 / 2000) Soil moisture (2050 / 2000) g/m 2 /s oCoC 850mb Wu et al., 2007

Summertime cyclone frequency decreases by 17% in the 2050s climate We are investigating links between calculated cyclone frequency and surface ozone. Wu et al., 2007 and Eric Liebensperger

Cumulative probability (%) Midwest Southeast Northeast Cumulative probability distributions of max 8-hr ozone (JJA) climate change has more effect on the pollution events than on the means? Max. 8-hr-avg ozone Cumulative probability (%) Max. 8-hr-avg ozone 2000 conditions 2050 climate 2050 emissions 2050 climate & emis Northeast Southeast Midwest Max. 8-hr-avg ozone Cumulative probability (%) climate change doesn’t effect SE ? median 99 th percentile Wu et al., 2007

Cumulative probability (%) Why does climate change have such a strong effect on pollution events? Max. 8-hr-avg ozone 2000s conditions 2050s climate 2050s emissions 2050s climate & emis median 99 th percentile Midwest Daily maximum temperature (K) Cumulative probability (%) Wu et al., 2007 Increased maximum temperatures during heat waves leads to increased ozone. Amplification of temperatures at extreme due to 1) soil moisture feedbacks and 2) decreased cyclone frequency.

Why is ozone in the Southeast insensitive to climate change? Isoprene has competing effects on ozone Isoprene emis +30%  Δ(O 3 ) / 2000 Isoprene emissions RO 2 + NO RONO 2 (sink for NO x ) Isoprene + OH RO 2 (OH sink) Isoprene + O 3 M (O 3 sink) O3O3 RO + NO 2 (O 3 formation) O3O3 Wu et al., 2007

Translating climate change penalty to emission control efforts 2000 conditions NOx emission - 40% (2000 climate) NOx emission - 40% (2050 climate) NOx emissions - 50% (2050 climate) 2000–2050 climate change implies an additional 25% effort in NOx emission controls to achieve the same ozone air quality. Wu et al., 2007 climate change penalty }

Summertime (June-August) afternoon background ozone (ppb) Wu et al., 2007 Large (3-5 ppb) increase over West due to Asian emissions. Background ozone: ozone over the United States as would exist in the absence of U.S. anthropogenic emissions

Climate effect on annual mean aerosol concentrations (  g m -3 ) is small. Climate effect is mainly through biogenic SOA and is small because of compensating factors (higher biogenic VOCs, higher volatility, precipitation ) concentrations 2050 climate Total PM2.5 SOA Wu et al., 2007

Most of the variability in wildfire frequency is due to year-to-year changes in surface temperatures and precipitation. Forest fires in western US have big impact on OC concentrations (50-60% in big fire years) Area burned and temperature in Canada over the last century Gillet et al., 2004 EPA wildfire project: How will changing forest fire frequency affect future air quality over the United States? What will happen next? Dominick Spracklen developed a fire prediction tool to calculate area burned using GISS GCM meteorological variables and beyond

Fire Prediction tool for the western U.S: 1)Regress observed met variables and drought indices against linear area burned. 2)Choose best predictors for each ecosystem. 3)Archive these predictors from GISS GCM for future climate. May-Oct mean obs TemperatureMay-Oct mean obs Drought Code R 2 =52% Area burned / 10 6 Ha observations model Regressions ‘explain’ 50-60% of variability in annual area burned in forest ecosystems. Best predictors are often temperature or Fuel Moisture Index. Sample results for Pacific Northwest/Cascade Forests. May-Oct Area burned Spracklen et al., 2007

Predicted mean biomass consumption by wildfires over the western United States for is 50% greater than for Use stochastic placement of wildfires within ecosystem and ecosystem specific fuel loads. Plot shows standardized departures from the mean. Annual total biomass consumed by forest fires, Spracklen et al., 2007

Current ( )Future ( ) Future-currentFuture / current Predicted changes to summertime (June-Aug) Organic Carbon concentrations over the US from GCAP model Summertime OC concentrations predicted to increase by ~30% over western US. We will continue this work with full-chemistry model. Largest OC increases are over Rockies and Pacific Northwest. Spracklen et al., 2007 Present-day OC makes up about 30-50% of total PM 2.5 over the western U.S.

A statistical method to study effects of climate change on air quality. Idea: Use probability of ozone exceedance + daily GCM maximum temperatures to predict number of exceedance days each summer in future. Step 1. find probability for each model day’s maximum temperature Step 2. likely number of exceedances = sum of probabilities for each summer Observed probability of ozone exceedance vs. daily max. temperature Lin et al Future temperature change over Northeast , calculated by many global climate models + = future smog episodes 1.2.

Summertime exceedances averaged over the Northeast, calculated using daily max temperatures statistically downscaled from three GCMs. If emissions of ozone precursors were to remain constant, exceedance days averaged over the Northeast would climb from 5 days per summer to by Advantage of method: Quick gauge of ozone sensitivity to climate and of climate penalty. Limitations: Assumes constant emissions of ozone precursors, and unvarying temperature + met variable relationships Also may not capture variability of exceedances. Same technique for PM 2.5 ? Lin et al., 2007 A1FI B1 observations CMAQ

Conclusions For A1B climate change, we calculate a10-20% decline in cyclone frequency, lengthening pollution episodes over Midwest and Northeast. Climate change is expected to degrade U.S. ozone air quality. The summer average daily max-8h ozone increases by 2-5 ppb over large areas due to climate change with the IPCC A1B scenario. Largest effect is during pollution episodes, when ozone increases by as much as 10 ppb. The climate change penalty corresponds to an additional 25% effort in NOx emission controls to achieve the same ozone air quality goals. Summertime OC concentrations are predicted to increase by ~30% over western US due to increasing wildfire frequency in the 2050s. Using observed ozone-temperature relationships, we find that climate change alone increases ozone exceedances over the Northeast US from 4.5 days per summer in 1990s to days by 2100.