1999 National Air Toxics Assessment (NATA) Madeleine Strum/Joe Touma USEPA/OAQPS Regional Modelers Workshop San Diego, CA May 17, 2006

Transcription

1 1999 National Air Toxics Assessment (NATA) Madeleine Strum/Joe Touma USEPA/OAQPS Regional Modelers Workshop San Diego, CA May 17, 2006

2 What you will learn What is NATA How can I use the results What can I do to help with future improvements 2

3 What is NATA? Characterization of air toxics across the nation Nationwide assessment with census tract resolution for 177 HAPs plus diesel PM Emissions, modeled ambient concentrations and estimated inhalation exposures from outdoor sources Cancer and noncancer risk estimates for the 133 HAPs Tools for State/Local/Tribal Agencies (and EPA) to prioritize pollutants, emission sources and locations of interest Provides a starting point for local-scale assessments Focuses community efforts Informs monitoring programs A few pieces of the air toxic puzzle 3

4 Components of the NATA National-Scale Assessment Dose- Response Assessment Emission Inventory Development Emission Processing (EMS-HAP) Air Dispersion Modeling (ASPEN) Inhalation Exposure Modeling (HAPEM) Risk Assessment/ Characterization 4 Comparison with Ambient Concentration Monitoring

5 1 NATA Emission Inventory Hazardous Air Pollutants Inventory (HAPs) Final 1999 National Emission Inventory (NEI) Version 3 Nearly all 188 HAPs, includes mobile and stationary sources Includes model parameters for many stationary sources Five major sources of data: State and local toxic air pollutant inventories (developed by State and local air pollution control agencies), Existing databases related to EPA's air toxics regulatory program, EPA's Toxic Release Inventory (TRI) database, Estimates developed using mobile source methodology (developed by EPA's Office of Transportation and Air Quality), and Emission estimates generated from emission factors and activity data 1999 National Emission Inventory for Criteria Pollutants For Diesel PM emissions Final 1999 NEI Version 3 Mobile source PM10 and PM2.5, subsetted for diesel engines Data from EPA s mobile models or state/local data where provided For Secondarily formed components of formaldehyde and acetaldehyde 1999 NEI Version 2 5

6 2 NATA Emission Processing Used EMS-HAP Version 3.0 Addresses Some Point Source QA Issues Defaults locations to census tract centroids, when insufficient information Defaults stack parameters where missing or out-of-range Prepares horizontal or fugitive emissions as non-stacked Defaults building parameters for smaller stacks Prepares emission inputs for ASPEN Temporally allocates annual emissions into eight 3-hour time blocks Spatially allocates the emissions that are at the county level to census tract level based on population and land-use characteristics Allocates airport-related emissions to the geographic coordinates of airports Generates the pollutants needed for the model and subsequent risk characterization Partitions metals into coarse and fine forms (account for different deposition rates) Speciates inventory into hexavalent and trivalent forms based on emission process Groups various forms of PAH into POM toxicity groups Assigns sources to source sectors : major, area & other, onroad and nonroad 6

7 3 NATA - Ambient Concentrations Model ASPEN Model Gaussian Model - ISCLT2 Uses 50 km radius around all sources Domain included 50 States, DC, Virgin Islands and Puerto Rico Added a background concentration for 28 HAPs: county-specific values generated for 13 HAPs based on monitoring study (2003), previous 96 NATA approach for remainder Predicted annual average ambient concentrations at each census tract for 4 source sectors (+ background) Limited model to monitor comparisons performed between predictions and monitoring data 7

8 NATA 1999 Model to Monitor Comparisons Model overprediction Benzene found very good agreement Metals appear to be underpredicted by NATA 1.0=Agreement Model underprediction 75 th percentile Benzene Carbon Tet Chloroform 1,4-Dichlorobenzene Ethylene Dichloride Methylene Dichloride Perc Trichloroethylene Acetaldehyde Formaldehyde Chromium Lead Manganese Nickel Median 25 th percentile

9 Summary of 1999 NATA Results at National Scale 9

10 Overall Summary of 1999 NATA Results The average cancer risk for 1999 is 42 in a million (1 in 23,800) This represents the subset of total air toxics cancer risk which can be quantified Benzene is most significant carcinogen* Comparable to 1996 NATA of 55 in a million (1 in 18,200) To put this in perspective: radon presents a risk of 2,000 in a million (1 in 500) However, emissions of radon are naturally produced it is estimated that one out of every three Americans will contract cancer during a lifetime, when all causes are taken into account. Two thirds of this risk is due to smoking or lifestyle factors The average noncancer risk for 1999 is 6.4 (hazard index for respiratory) Acrolein a majority of this risk Comparable to 1996 NATA of 5.2 Some new air toxics added to list of significant pollutants Confirmed list of 33 urban air toxics as primary risk drivers Note: This is an estimate of the average American s chance of contracting cancer from breathing the air toxics analyzed here, if they were exposed to 1999 emissions levels for 70 years. This assessment does not include indoor air, diesel emissions, noninhalation exposure pathways. Risks from PM and other criteria pollutants are not included in this assessment. 10

11 Which air toxics are most important & what are the key source categories? 11

12 1999 National-Scale Assessment Risk Characterization - Significant Pollutants Cancer National drivers 1 Benzene Regional drivers 2 Arsenic compounds Benzidine 1,3-Butadiene Cadmium compounds Carbon Tetrachloride Chromium 6 Coke oven Ethylene oxide Hydrazine Naphthalene Perchloroethylene POM 1 At least 25 million people exposed to risk > 10 in 1 million 2 At least 1 million people exposed to risk > 10 in 1 million OR At least 10,000 people exposed to risk > 100 in 1 million Non-Cancer National drivers 3 Acrolein Regional drivers 4 Antimony Arsenic Compounds 1,3-Butadiene Cadmium compounds Chlorine Chromium 6 Diesel PM Formaldehyde Hexamethylene 1-6-diisocyanate Hydrazine Hydrochloric acid Maleic anhydride Manganese compounds Nickel compounds 2,4-Toluene Diisocyanate Triethylamine 3 At least 25 million people exposed to a hazard quotient (HQ) > At least 10,000 people exposed to HQ >1 Blue indicates new drivers since

13 1999 NATA Cancer Risk Source Sector Contributions Average Risk: 42 in a million 10% 42% Major 19% Background Area/Other Onroad Nonroad 5% 24% Note: NATA does not include radon, indoor air, diesel emissions, dioxins, or noninhalation exposure pathways. 13

14 1999 NATA - Pollutant Contribution to Average Cancer Risk (42 in a million) POM Group_2 1% Hydrazine 1% Ethylene oxide 1% Other 8% p Dichlorobenzene 1% Benzene 24% Ethylene_dichloride 2% Chromium VI 4% Tetrachloroethylene 4% Coke Oven Emissions 4% Naphthalene 5% Ethylene dibromide 9% Bis 2 ethylhexyl phthalate 5% 1,1,2,2 Tetrachloroethane 6% Butadiene 9% Acetaldehyde 7% Carbon tetrachloride 8% Note: NATA does not include radon, indoor air, diesel emissions, dioxins, or non-inhalation exposure pathways.

15 Where are the locations of greatest air toxic risk of concern? 15

16 Risk Geographic Distribution Cancer Risk Majority of country predicted to have risk between 1 and 25 in a million Most urban locations greater than 25 in a million Transportation corridors and some locations greater than 50 in a million risk Just a few counties greater than 100 in a million risk Noncancer Over 40% of counties hazard index greater than 1 Just a few counties hazard index greater than greater than 10 High values in Florida from forest fires (they are using different emission factors) 16

17 1999 NATA Scale Assessment 1999 NATA -- National National Scale Assessment Predicted CountyLevel Level Noncancer (Respiratory) Risk Predicted County Noncancer (Respiratory) Risk Median Risk Level Hazard Index Over 40% of counties hazard index greater than 1 Several counties hazard index greater than greater than 10 High values in Florida from forest fires

18 1999 NATA - National Scale Assessment Predicted County Level Cancer Risk County Medians Median Risk Level <1 in a Million 1-25 in a Million in a Million in a Million in a Million >100 in a Million Spatially, most of country predicted to have risk between 1 and 25 in a million Most urban locations greater than 25 in a million Transportation corridors and some locations greater than 50 in a million Several counties greater than 100 in a million

19 What do the NATA Results Mean? Risk results highly variable from location to location Like any assessment of this magnitude, the results have their limitations and contain a degree of uncertainty Model-to-monitor results generally show good agreement for volatiles and under prediction for metals Model resolution can miss local impacts (e.g., hot spots near large polluters) Inhalation pathway, chronic exposures only Higher risks levels highlight areas for further refinements (i.e., local scale assessments, inventory improvements, monitoring) 19

20 Room for Future Improvements Need to better address chemical transformation Need to better address background long range transport concentrations Treatment of area sources as pseudo point sources misses hot spots especially next to near roadways Need a distribution of concentrations in the census tract instead of just at tract centroid Tends to underestimate metals- deposition or fugitive source characterization? Do you have any ideas for how we can do things better? 20

21 An Approach to Provide Local Details from Dispersion Model to CMAQ: ASPEN and CMAQ combination Procedure: (ASPEN ASPEN AVG ) + CMAQ 1) Calculate ASPEN average for each CMAQ grid cell (ASPEN AVG ) 2) Calculate ASPEN differences at each receptor: (ASPEN ASPEN AVG ) 3) Add ASPEN differences and CMAQ values for each cell Note: If negative ((ASPEN ASPEN AVG )+CMAQ < 0) check inventory CMAQ Combined ASPEN ASPEN AVG 21

22 ASPEN BENZENE CMAQ ASPEN + CMAQ ASPEN FORMALDEHYDE CMAQ ASPEN+CMAQ 22

23 Examining Geographic Distribution of Risk Provides Opportunities for Integrated, Multi-pollutant Assessments 1999 NATA - National Scale Assessment Predicted County Level Carcinogenic Risk (from HAPEM5) 1999 NATA- National Scale Assessment Predicted County Level Carcinogenic Risk (from modeled exposures) 2010 remaining issues Ozone Median Risk Level PM <1 in a Million 1-25 in a Million in a Million in a Million in a Million >100 in a Million Both PM and Ozone Some areas of predicted high risk are expected to have O3 and PM problems in the future (2010) 23