Recent and future changes in high surface ozone events over the Eastern United States

Transcription

1 Recent and future changes in high surface ozone events over the Eastern United States Harald E. Rieder 1,2* and Arlene M. Fiore 1,3 1 Lamont-Doherty Earth Observatory, Columbia University, NY, USA 2 Applied Physics and Applied Mathematics, Columbia University, NY, USA 3 Earth and Environmental Sciences, Columbia University, NY, USA Atmospheric Chemistry Meeting 16 JULY 2013 Lamont-Doherty Earth Observatory Columbia University, New York, USA

2 Changes in high ozone events over the observational time period

3 MOTIVATION 1) National Ambient Air Quality Standards have tightened over recent decades 2) Improved air quality policy provides ancillary benefits for human health and reduces health system costs [e.g., Bell et al., 2008] 3) changes in climate, as well as regional and global emissions are expected to influence the frequency, duration, and intensity of air pollution events above the NAAQS thresholds [e.g. Turner et al., 2013] 4) observations demonstrate that high air pollution (O3 and PM2.5) is typically associated with stagnation events (heat waves) (e.g., Logan, 1989, Vieno et al., 2010) 5) inter-annual variability of extreme air pollution events may increase, along with their persistence [e.g. Meleux et al., 2007] 6) rich observational data base (e.g., CASTNET, AQS, EMEP) 7) recent development in EVT models 8) continuous improvement in atmospheric chemistry models

4 CASTNET SITES & SITE SELECTION - Clean Air Status and Trends Network (CASTNET) data for the Eastern US - in operation since operational sites SELECTION CRITERION: at least 20 years of data in the time period 23 out of 31 stations we analyze three regions of interest following Rasmussen et al. (2011) Data available at:

5 EVT MODELLING We use a Peak-Over Threshold (POT) approach to model days above the NAAQS MDA8 O 3 standard of 75 ppb using the Generalized Pareto Distribution (GPD) F( x) ( x u) 1 1 1/ u the threshold value (75 ppb) σ > 0 is the scale parameter ξ ϵ R is the shape parameter Sample site: Penn-State (PSU106) Gaussian vs. Observations GPD vs. Observations [Rieder et al. 2013]

6 EVT MODELLING From the fitted GPD we can derive the T-year return level x T, defined through the relation F(x T )=1-1/T, which describes the probability to observe a value x within a time window T. To analyze if changes in the NAAQS MDA8 O 3 threshold had a significant influence on NE US air quality we calculate the return levels of x T for two 11-year time periods and at each station. Return Level within a given time period (T) [Rieder et al. 2013]

7 MDA8 O 3 RETURN LEVELS ABOVE THE NAAQS 1-year return levels year return levels to : 1-yr return level decreases by 2-16 ppb avg. 8 ppb -Large parts of the NE US show 1-yr return levels below 100 ppb in

8 Comparing CASTNET and CM3 for the historical time period

9 CASTNET vs. CM3 - Offset between CM3 PDF and CASTNET PDF HOWEVER: CM3 shows very similar response to NOx-SIPCALL as CASTNET SITES i.e, larger reductions for higher quantiles IDEA: Use quantile-mapping to correct CM3 PDF for MDA8-O3

10 Model Bias Correction through Quantile Mapping GOAL: establish a statistical relationship or transfer function between model output and observations based on historical data Quantile-based mapping approach maps the distribution of model variables on the observed data (first introduced by Panofsky and Brier, 1968) P O = h(p M )

11 Quantile Mapping Results

12 Quantile Mapping Results - PDF of QM-corrected CM3 matches CASTNET PDF - Mean-Bias correction improves agreement with the observations though various biases remain QM-correction superior to mean-bias correction ALSO NOTE: QM-correction preserves local differences (in time) on grid-cell basis

13 Quantile Mapping Results Mean MDA8O3 ORIGINAL-CM3 QMcorrected-CM3 OCM3: overestimates observed Mean MDA8-O3 by 5-20ppb on grid cell basis QMCM3: matches observed Mean MDA8-O3 very well

14 Quantile Mapping Results - # days above the NAAQS OCM3: largely overestimates #days above the NAAQS (~ factor of 2) QMCM3: matches #days above the NAAQS and provides realistic spatial representation ORIGINAL-CM3 QMcorrected-CM3

15 Changes in Eastern US high ozone events under different representative concentration pathways

16 GFDL-CM3 Model & RCPs GFDL-CM3 with coupled chemistry for IPCC AR5 RCP-scenarios [2.5 x 2 grid] RCP4.5: increasing CO2 & decreasing methane (global T ~2 C by flattens) RCP4.5X: as RCP4.5 but with constant NOx emissions (year 2000 level) RCP8.5: increasing CO2 & increasing methane (global T ~4 C by rises) RCP8.5 RCP4.5 Source: Van Vuuren et al., 2011 [modified]

17 climate change + decreasing O3 precursors TIME - Strong decline in MDA8-O3 with thime - Stronger decline in high quantiles than low quantiles - QMcorrected-CM3 preserves rate of decline over quantile range AND corrects overall pdf for high biases in CM3

18 climate change + decreasing O3 precursors MEAN change vs MEAN change vs Q90 Q10 change change vs vs Q90 change vs

19 climate change only scenario - Very stable PDF over the 21 st century (constant emissions!) - Though small increase in MDA8-O3 over quantile range (~1-2ppb) climate penalty - Not much difference between the low and high tails and bulk of the PDF MEAN change vs MEAN change vs

20 climate change only scenario - HOWEVER spatial differences in MDA8-O3 - increases in MDA8-O3 along the coast and towards higher latitudes - Stronger climate penalty as time evolves MEAN change vs MEAN change vs

21 Changes in the number of days above the NAAQS RCP change vs RCP4.5* 0 50 change vs change vs change vs RCP4.5: strong decline in #days above the NAAQS over 21 st century no exeedance by mid century RCP4.5*: larger #days above NAAQS at beginning of 21 st century than RCP4.5 increase in the number of non-compliance days (up to +10) along the coast (region with current highest non compliance rate)

22 Changes in 1-year return level estimates RCP RCP4.5: strong decline in the 1 year return level (RL) 1-yr RL well below 75pbb for the entire eastern US by mid 21 st century by yr RL at most by 60 ppb (!sic NAAQS results)

23 Changes in 1-year return level estimates RCP RCP4.5* RCP4.5: strong decline in the 1 year return level (RL) 1-yr RL well below 75pbb for the entire eastern US by mid 21 st century by yr RL at most by 60 ppb (!sic NAAQS results) RCP4.5*: 1 year return level (RL) way higher than under RCP4.5 as time evolves increasing RLs with time climate penalty

24 Changes in 1-year return level estimates RCP4.5*: 1 year return level (RL) way higher than under RCP4.5 increasing RLs with time about 2-4 ppb increase in 1-yr RLs strongest increase in 1-yr RL along the coast and at higher latitudes?? changes in atmospheric dynamics?? RCP4.5* change vs change vs change vs

25 CONCLUSIONS improvement in Eastern US air quality following the NOx SIP Call Return level analysis is a useful tool to illustrate these changes GFDL CM3 is found to be biased high compared to observations Quantile Mapping is a useful approach to correct model bias Quantile Mapping preserves spatio-temporal structure of CM3 Quantile Mapping allows to estimate changes in MDA8O3 on local/regional scale Future development of US air quality depends strongly on the RCP followed optimistic scenario (RCP4.5) strong improvement in O 3 pollution (RCP4.5) Strong decline in non-compliance days and probabilistic return levels pessimistic scenario (RCP4.5X) almost no changes to 2000 levels slight increases in # non compliance days and RL along the Coast and higher latitudes

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27 METHOD Goal is to correct the distribution of CM3 (M) to CASTNET (O) P O = h(p M ) first we derive selected quantiles (i) from both M and O i = min, P(0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.99), max next we calculate the difference (D) at step i between M and O D i = M i O i next we calculate the difference (x,y) between i+1 and i for M and O x i = M i+1 M i y i = O i+1 O i next we calculate the ratio (R) of x and y at step i R i = x i y i next we perform a stepwise correction (Z j ) Z j = (M i D i ) + (R i j) for(m i,, M i+xi ), j={0,, x i 1 }

28 Climate Change only scenario Q10 change vs Q10 change vs Q75 change vs Q75 change vs

29 Changes in the number of days above the NAAQS RCP change vs change vs RCP4.5* change vs change vs HYPOTHETICAL Lower NAAQS of 60 ppb RCP4.5: strong decline in #days above NAAQS over 21 st century only limited number of exceedances by 2100 RCP4.5*: larger #days above NAAQS at beginning of 21 st century than RCP4.5 further increase in non compliance days (up to +6 days) as climate warms