Issues and Research at UCR on PM and Toxics Impacts of VOCs

Transcription

1 Issues and Research at UCR on PM and Toxics Impacts of VOCs William P. L. Carter CE-CERT, University of California, Riverside, CA May 28, 2009 Outline Factors affecting impacts of VOCs on secondary toxics and modeling study of aldehyde and PAN formation potentials of VOCs Factors affecting impacts of VOCs on PM and qualitative UCR chamber data on relative impacts of coatings VOCs Summary of issues and research needs for developing reactivity scales for impacts of VOCs on SOA and toxic products W. P. L. Carter 5/25/2009 PM and Toxics Reactivities of VOCs 1

2 Factors Affecting Impacts of VOCs on Air Toxics Formation Direct Effects For toxic VOCs the main factors are their removal rates For toxic precursor VOCs the main factors are the rate the VOCs react, the toxic product yields and how they vary with conditions Indirect Effects VOCs that enhance or inhibit radical levels will affect rate of toxic product formation from toxic precursors that are present VOCs that affect O 3 will affect the chemical environment that may affect some toxic product yields (e.g., PANs) Indirect effects will be highly dependent on the levels of toxic precursors present Indirect effects will correlate with O 3 reactivity more than direct effects. W. P. L. Carter 5/25/2009 PM and Toxics Reactivities of VOCs 2

3 UCR Project for OEHHA to Estimate Aldehyde and PAN Formation Potentials Background The California Office of Environmental Health Hazard Assessment needed to evaluate the human and environmental health impacts of motor vehicle fuels Quantifying effects on secondary toxics of fuel VOCs on air toxics (aldehydes, nitrates, PANs) was part of this effort UCR was contracted to calculate impacts of VOCs on atmospheric aldehyde, nitrate, and PAN levels Work was completed in September, Report now available at W. P. L. Carter 5/25/2009 PM and Toxics Reactivities of VOCs 3

4 Project to Estimate Aldehyde and PAN Formation Potentials: Approach SAPRC-99 mechanism used Duplicate organic product species added to permit separate assessments of direct and indirect effects Same scenarios employed as used to calculate MIR, MOIR, and EBIR ozone reactivity scales Incremental reactivities of VOCs were calculated with respect to direct and indirect formation of: Formaldehyde PAN Acrolein Acetaldehyde PBzN Organic nitrates Lumped higher aldehydes Lumped Other PANs Lumped aromatic products W. P. L. Carter 5/25/2009 PM and Toxics Reactivities of VOCs 4

5 Direct and Indirect Acetaldehyde and PAN Formation Potentials vs. Ozone Reactivity MIR Scenarios EBIR Scenarios Acetaldehyde PAN Acetaldehyde or PAN Formation Potential (molar) Direct Indirect Ozone Reactivity (molar) W. P. L. Carter 5/25/2009 PM and Toxics Reactivities of VOCs 5

6 Aldehyde and PAN Formation Potentials in High vs. Low NO x Scenarios Formation Potential in EBIR (Low NOx) Scenarios Formaldehyde PAN Acetaldehyde :1 Line PBzN Formation Potential in MIR (High NOx) Scenarios W. P. L. Carter 5/25/2009 PM and Toxics Reactivities of VOCs 6

7 Aldehyde and PAN Formation Potentials vs. Ozone Reactivity in MOIR Scenarios Formaldehyde Acetaldehyde Acetaldehyde or PAN Formation Potential (molar) PAN Ozone Reactivity (molar) PBzN W. P. L. Carter 5/25/2009 PM and Toxics Reactivities of VOCs 7

8 Summary and Recommendations - Toxic Product Reactivity Summary Toxic product reactivities depend on details of VOC mechanisms which vary from compound to compound Aldehyde formation potentials are insensitive to NO x conditions. PAN potentials more sensitive but trends are consistent. Correlation with O 3 reactivity depends on product. Ranking is PAN > Formaldehyde > Acetaldehyde >> PBzN Recommendations Issues and research needs similar to those for O 3 scales except: Greater requirement for chemical detail in mechanism and greater mechanism uncertainty Choice of scenario conditions may be slightly less important except for composition of base ROG mixture. W. P. L. Carter 5/25/2009 PM and Toxics Reactivities of VOCs 8

9 Factors Affecting Impacts of VOCs on Secondary PM Many VOCs form low volatility oxidation products that can partition into the aerosol phase and contribute to secondary PM Some higher volatility products may also partition into the aerosol phase due to heterogeneous reactions The yields of condensable products varies from compound to compound and with atmospheric conditions Identity, yields, formation mechanisms, partitioning coefficients, and heterogeneous reactions of condensable products are mostly unknown for most VOCs Data and mechanistic knowledge are inadequate for models to predict secondary PM from VOCs with any degree of reliability. Current models use inadequately tested and highly simplified parameterized models to predict secondary PM W. P. L. Carter 5/25/2009 PM and Toxics Reactivities of VOCs 9

10 Requirements for Predictions of PM Impacts (in addition to requirements for O 3 predictions) Predictive Mechanisms for Chemical and Physical Processes Chemical mechanism must predict yields of low-volatility products and how they change with chemical conditions Predict gas-to-particle phase partitioning and evaporation Predict condensed-phase reactions (polymerization, etc) Predict PM nucleation and removal processes Model for Environmental Conditions Appropriately representing temperature, humidity, absolute concentrations much more important for PM than for O 3 Appropriately represent primary and background PM that may affect partitioning or condensed-phase processes Use base case scenarios that give representative PM levels Appropriately represent PM loss processes W. P. L. Carter 5/25/2009 PM and Toxics Reactivities of VOCs 10

11 PM Measurements in the UCR EPA Chamber PM Measurements were made in conjunction with most recent ozone reactivity experiments. Compounds studied include: Representative Water- and Solvent-based coatings VOCs Several pesticide VOCs: MITC, EPTC, CS 2, Kerosene Aminomethylpropanol (AMP), Aminoethanol, d-limonene Research underway to determine effects of reactant (e.g. NO x ) concentrations, humidity, and other factors on PM formation Current emphasis is on aromatics and terpenes Data obtained are needed to develop predictive mechanisms for PM formation in the atmosphere Experiments are being carried out at lower reactant concentrations than is practical for most other chambers A large array of state-of-science equipment recently was obtained from a grant from the Keck foundation W. P. L. Carter 5/25/2009 PM and Toxics Reactivities of VOCs 11

12 Representative PM Data from Reactivity Experiments PM Number (/m 3 ) PM Volume (µg/m 3 ) Irradation time (hours) Base Experiment (30 ppb NOx, 0.6 ppmc Base ROG) 1.5 ppmc Kerosene Added W. P. L. Carter 5/25/2009 PM and Toxics Reactivities of VOCs 12

13 25% Average PM Reactivities in Incremental Reactivity Experiments 20% 15% 10% 1% 5 Hour PM Mass relative to amount of VOC added 5% 0% Ethanolamine d-limonene Benzyl alcohol AMP Kerosene 2-Butoxyethanol 2-(2-butoxyethoxy)-ethanol EPTC MITC ASTM-1A Aromatic 100 ASTM-1B CS2 ASTM-1C ASTM-3C1 Texanol VMP Naphtha Eth. & Prop. Glycols (uncorrected for wall loss) W. P. L. Carter 5/25/2009 PM and Toxics Reactivities of VOCs 13

14 Comparison of SOA in Experiments with Same Initial m-xylene Concentrations PM M o(µ g/m 3 ) dn/dlogdp UCR EPA Chamber ppb m-xylene ppb NOx Diameter(nm) EPA219B(NOx:9ppb) EPA220B(NOx:60ppb) EPA222B(NOx:166ppb) EPA223B(NOx:266ppb) 9 ppb NOx 60 ppb NOx Reacted HC(µg/m 3 ) 223 ppb NOx 166 ppb NOx W. P. L. Carter 5/25/2009 PM and Toxics Reactivities of VOCs 14

15 Upcoming UCR Project: SOA Formation: Chamber Study and Model Development Objectives: Develop improved mechanisms to predict secondary organic aerosol (SOA) from aromatics and other compounds. Status: Contract pending Proposed Overall Approach: This project to be carried out in collaboration with Dr. David Cocker at UCR and Dr. Robert Griffin at Rice University. UCR EPA chamber experiments will be conducted to develop and evaluate models for SOA from aromatics, aromatic products, and selected other VOCs The SAPRC-07 mechanism will be expanded and adapted for SOA modeling based on the results of the experiments. Use the results to develop improved mechanisms for predicting SOA in 3-D airshed models. W. P. L. Carter 5/25/2009 PM and Toxics Reactivities of VOCs 15

16 Summary and Recommendations - PM Reactivity: Scientific Issues Chamber data indicate VOCs vary significantly in PM impacts, and PM impacts are not correlated with O 3 impacts. However, current data are qualitative and not representative of ambient conditions Improved, and more comprehensive mechanisms need to be developed for modeling secondary PM in the atmosphere Detailed mechanisms have been developed for only few of VOCs and evaluated under unrepresentative conditions Current simplified PM models are not consistent with the limited available chamber data for aromatics Well-characterized chamber experiments simulating ambient conditions are needed to develop predictive PM models. Scenarios for assessing PM impacts need to be developed. Existing scenarios for O 3 reactivity scales are not appropriate W. P. L. Carter 5/25/2009 PM and Toxics Reactivities of VOCs 16

17 Summary and Recommendations - PM Reactivity: Policy Issues Current models are not yet sufficiently reliable to serve as a basis for deriving PM reactivity scales for regulatory applications Near term solution: Use PM formation in appropriate environmental chamber experiments to obtain qualitative PM reactivity rankings Modeling and experimental research is needed to develop appropriate experimental procedures for this purpose Longer term solution: Continue to support experimental and model development research to improve SOA models. Once sufficiently reliable models are developed, the issues become similar to those for O 3 and toxics reactivity scales. W. P. L. Carter 5/25/2009 PM and Toxics Reactivities of VOCs 17

18 Additional Information Available W.P.L. Carter research on chemical mechanisms and reactivity Report on Aldehyde and PAN formation potentials for the California OEHHA (Dated September 23, 2001) Research on Secondary Organic Aerosol Formation in UCR EPA chamber W. P. L. Carter 5/25/2009 PM and Toxics Reactivities of VOCs 18