U.S.-Canada Air Quality Agreement: Transboundary PM Science Assessment Report to the Air Quality Committee June, 2004

Transboundary PM Science Assessment Background: Requirement of the 1998 Joint Work Plan for PM Product of three bi-national workshops between Tailored to address the information needs of the policy community Reviewed externally by both Canadian and U.S. reviewers; comments addressed prior to the June meeting Purpose: Synthesize current atmospheric science of PM 2.5 in keeping with information needs of Subcommittee 1, summarized in seven Assessment objectives.

PM Assessment Objectives 1.Identify whether or not there is a fine PM problem in the border regions with a focus on health, visibility and environmental endpoints; 2.Identify the extent of the problem; 3.Describe the PM issue in terms of geographic regions; 4.Identify PM precursors of concern on a regional or sub-regional basis; 5.Describe sources (or source regions) of PM and PM precursors in the context of geographic regions; 6.Describe emissions of PM precursors, the spatial distribution of emissions and the transport characteristics of these emissions and, 7.Identify the current and proposed emission reductions scenarios on fine PM levels in North America.

Assessment Status Science document was completed and externally peer reviewed by parties in both Canada and the United States Reviewer comments have been addressed to the extent possible at this time A final document will be made available publicly after technical edit, layout and translation.

Air Quality Standards Canada: –98 th percentile, 24 hour average, averaged over 3 consecutive years of 30 µg/m 3, to be achieved by 2010 U.S: –Annual: 15 µg/m 3 based upon a 3 year average of the annual arithmetic mean –24-hour: 65 µg/m 3 based on 98 th percentile, 24 hour average, averaged over 3 years

Ambient Air Quality Levels of PM 2.5 exceed both Canadian and U.S. air quality standards in several regions mean PM 2.5 levels, many sites over 15 µg/m 3, particularly in the northeast

Ambient Air Quality 98 th percentile values over 30 µg/m 3 (yellow dots) over a majority of the northeastern U.S. (some in Canada) Also elevated concentrations in the northwestern U.S.

Ambient Air Quality – United States PM 2.5 trend Mean/98 th percentile W-E

Ambient Air Quality – Canada PM 2.5 trend th percentile W-E 2001

Ambient Air Quality - Characterization Urban PM 2.5 speciation graphs (EPA and NAPS speciation sites): eastern regions dominated by carbon compounds and sulfate; west dominated by carbon compounds and nitrate. Both nitrate and sulfate are associated with particle ammonium.

Emissions Base case emissions of SO 2 and NO x are concentrated in the industrial Midwest, northeastern United States, and southern Ontario Emissions of NH 3 are concentrated further west in the central Midwest region.

Model Applications Three models were used to evaluate the impact of current and proposed commitments on air quality in the transboundary region. REMSAD: v.7.06, 5 scenarios, full year runs for PM and PM constituents AURAMS: v.0.30a, 5 scenarios, 2 two-week episodic evaluations (summer & winter) for PM and PM constituents REMSAD and AURAMS scenarios: 1996 base case, 2010 base and control, 2020 base and control CMAQ: for the northwestern domain, summer and winter simulations run for PM and ozone, turning off either U.S. or Canadian emissions

Model Applications – REMSAD Predicted reductions in annual PM 2.5 levels up to 2.3 µg/m 3, sulfate reductions up to 1.4 µg/m Control Case vs Base Case

Model Applications – REMSAD Predicted reductions in annual nitrate levels up to 0.6 µg/m 3, ammonium reductions up to 0.5 µg/m Control Case vs Base Case

Model Applications – AURAMS Total PM 2.5 reductions of up to 2.4 µg/m 3 Episodic evaluation indicates SO 4 and NH 4 reductions up to 1.5 µg/m 3 NO 3 substitution may result in increased NO 3 levels in some regions (up to 1.5 µg/m 3 ), and possibly increasing total PM 2.5 concentrations in some areas in the winter Winter episode

Model Applications – AURAMS Summer episode evaluation indicates reductions in total PM 2.5 of up to 6 µg/m 3, driven by reductions in SO 4 and NH 4. Summer episode

Model Applications - CMAQ Ambient concentrations are predicted to both increase and decrease in various regions of western North America, correlated to increases in primary PM, marine and agricultural emissions forecasts for 2010 and 2020 Summer episode Base case

Source-Receptor Analyses A wide variety of source-receptor analyses were carried out in both countries, in order to quantify the relationship between sources and measured ambient PM and PM precursor levels These methods include: –Observational receptor-oriented analyses –Positive Matrix Factorization (PMF) –Principal Component Analysis (PCA) Space-based observations can also aid in the observation of PM episodes in North America

Source-Receptor Analyses Emissions of PM and PM precursors from the eastern U.S. and southern Canada have an impact on PM 2.5 levels in both countries. PM µg/m 3 PM µg/m 3 Simple Trajectory Analysis

Source-Receptor Analyses More complex trajectory analysis indicates that air transported from the Ohio River Valley was most often associated with high PM concentrations. Observation-based findings are consistent with the spatial distribution of emissions. Quantitative Transport Bias Analysis

Source-Receptor Analyses Regions of influence identified, and indicate the highest probability of three types of coal-related sources influencing PM 2.5 in the border region Correlates well with high density emission areas for SO 2 and NO x Incremental Probability Technique

Source-Receptor Analyses Model applications in combination with source-receptor analyses indicate that there is evidence of transboundary transport of both NH 3 and NH 4. Incremental Probability Technique

Source-Receptor Analyses Regional transport of sulfate implies regional transport of PM 2.5, while carbon components are more local in nature Urban Excess Analysis

Natural Contributions of PM Wild and prescribed forest fires can impact air quality on both an episodic and long-term average basis over wide regions Quebec, Canada forest fires July, 2002

Satellite Observations of Aerosol Optical Depth Composites of aerosol optical depth and cloud optical depth superimposed over continuous PM 2.5 (bars) for July 6 th, Hourly PM 2.5 concentration is indicated by the height of the bar, while bar color represents the 24 hour running average mass concentration color coded to the US EPA Air Quality Index The yellow to red colors of aerosol optical depth show elevated aerosol concentrations, correlated strongly with PM 2.5 levels.

Co-benefits of Emissions Reductions Implementation of existing and proposed controls will have a positive effect on other air quality issues, including ground-level ozone, sulfate and nitrate deposition. Ozone levels are predicted to decrease by a maximum of 16 ppb over much of the northeastern U.S, based on AURAMS output.

Co-benefits of Emission Reductions Reductions predicted up to 6 kg/ha SO 4 and 4 kg/ha NO 3 wet deposition, based on REMSAD output Widespread exceedence of forest critical loads in eastern Canada

Co-benefits of Emission Reductions Sulfate is a key contributor to annual visibility reduction in the U.S. Visibility is reduced (particularly in the warm season), in a large portion of the border region

Outcome of External Peer Review Outcome of the peer review was generally positive, with a few minor issues to resolve. The key issues include: –Representativeness of measurement sites –Uncertainties in emissions inventory information and process parameterization for air quality models –Incomplete model evaluation for AURAMS, CMAQ and REMSAD –Emphasized the need for precise quantification of transboundary flow of PM and PM precursors Have addressed the reviewer comments where possible and the resulting revisions did not change the conclusions of the report.

Conclusions A variety of analytical techniques were used in both countries to provide a weight of evidence approach on PM in the border region. These include observations, model applications and source-receptor analyses. There is evidence illustrating transboundary flow between the two countries that would support further policy discussions. PM 2.5 and its constituents (SO 4, NO 3, NH 4 ) are of concern in the transboundary region, although the concentrations of these pollutants vary geographically. Sources contributing to PM 2.5 in the border region include industrial point source emissions, vehicle emissions, and road dust. The formation of PM from precursors including SO 2, NO x and NH 3 is also significant.

Conclusions Transport of PM and PM precursors from the U.S. to Canada appears to be greater than transport from Canada to the U.S. The largest predicted air quality improvements occur in the areas of the largest predicted emission reductions; however, improvements are seen regionwide. The primary areas of concern for transport are in the east; additional areas of concern are the Canadian Prairie/U.S. Northern Plains, where visibility is an issue, and the west coast. In the west, PM appears to be primarily a sub-regional problem. Reductions in PM and PM precursors have co-benefits on other air quality issues, including ground level ozone, acid deposition and visibility.