Final Report: Impact of Global Change on Urban Air Quality via Changes in Mobile Source Emissions, Background Concentrations, and Regional Scale Meteorological Feedbacks

EPA Grant Number: R833372
Title: Impact of Global Change on Urban Air Quality via Changes in Mobile Source Emissions, Background Concentrations, and Regional Scale Meteorological Feedbacks
Investigators: Kleeman, Michael J. , Chen, Shuhua , Schauer, James J.
Institution: University of California - Davis , University of Wisconsin Madison
EPA Project Officer: Hunt, Sherri
Project Period: March 1, 2007 through February 28, 2011 (Extended to February 28, 2013)
Project Amount: $900,000
RFA: Consequences of Global Change For Air Quality (2006) RFA Text |  Recipients Lists
Research Category: Climate Change , Air , Global Climate Change

Objective:

California has persistent air quality problems that affect the health of 30+ million residents. Predicting future air quality in California is a complex task because of three factors: (1) emissions will change in response to control programs that include the adoption of new fuels/technologies, (2) meteorology will change in response to the evolving climate, and (3) feedbacks between regional pollution and regional meteorology can lead to non-linear interactions between factors (1) and (2). All of these issues are exacerbated by California’s complex topography and large diverse economy. A coordinated program of emissions measurements and advanced model predictions is needed to predict future air quality in California.

Summary/Accomplishments (Outputs/Outcomes):

Methods: Emissions from vehicles powered by biofuels (ethanol + gasoline blends and biodiesel + petroleum diesel blends) were measured using a dilution sampling system. Gas-phase and particle-phase emissions were collected using a denuder-filter-PUF sampling train and analyzed for a wide range of compounds. The response of emissions to different temperatures was measured by manipulating the temperature of the dilution air in these tests. Different fuel additives were also tested to determine how they affected emissions.

A source-oriented version of the publically available WRF/Chem model was created to explicitly calculate the aerosol mixing state in the atmosphere. The source-oriented WRF/Chem (SOWC) model predicts the rate at which primary particles from different sources become coated by secondary PM components such as sulfates, nitrates, and SOA. The rate at which absorbing particles become coated affects the optical properties of the atmosphere, which in turn affects the distribution of radiant energy and the related meteorological parameters. Further development of the SOWC model was carried out to include warm-cloud processes and large eddy simulation (LES) that can support studies at high resolution (250m).

The new SOWC model was applied to three present-climate episodes in California to test different dimensions of model performance. The new measurements and modeling system were then applied to predict the PM2.5 concentrations across California with and without adoption of California Assembly Bill 32 (Global Warming Solutions Act of 2006) during an extreme future climate air pollution episode.

Measurement Results: PM2.5 mass emissions rates for the B25, B50 and B75 soybean oil biodiesel mixtures had 20-30 percent lower emissions than the petroleum diesel, but B100 emissions were about 40 percent higher than the petroleum diesel. The trends in mass emission rates with the increasing biodiesel content can be explained by a significant decrease in elemental carbon (EC) emissions across all blending ranges and increasing organic carbon (OC) emissions with pure biodiesel. Beef tallow biodiesel blends showed similar trends. The results show that the use of biodiesel fuel for economic or climate change mitigation purposes can lead to reductions in PM emissions and a co-benefit of EC emission reductions.


Figure 1. Fine particle mass, OC and EC emissions rates from different blends of petroleum diesel and biodiesel derived from soybean oil and beef tallow.

The use of platinum-cerium bimetallic fuel additive had a significant impact on the detailed chemical composition and size distribution of particulate matter emitted from a diesel engine. A 0.1 ppm-Pt and 7.5 ppm-Ce additive reduced the emissions of PM2.5 mass by 34 percent, PM2.5 EC by 54 percent, and PM2.5 OC by 23 percent.

Experiments conducted to examine the impact of temperature on emissions from vehicles powered by ethanol-gasoline mixtures and compressed natural gas (CNG) showed no clear impact on fine particle emissions for dilution air temperatures ranging from 60 to– 80oF. Increased ethanol content in flex-fuel vehicles did reduce the particle number emissions rate.

Model Results: A source-oriented representation of airborne particulate matter was added to the Weather Research & Forecasting (WRF) model with chemistry (WRF/Chem). Initial tests over a 3-week stagnation episode (December 15, 2000 to January 6, 2001) demonstrated that the source-oriented approach yields different aerosol optical properties than internal mixture calculations because particles emitted from diesel engines do not become coated by secondary nitrate as quickly. PM concentrations predicted by the source-oriented WRF/Chem (SOWC) model are 3-7 percent lower than the internally mixed version of the same model because increased solar radiation at the ground increases atmospheric mixing.

(a)    Source-oriented mixing
(b) Internal mixing

Figure 2. Source-oriented and internal mixing state of the particles at noon on December 24, 2000, at surface level in Fresno, California. Total PM concentrations are similar in both cases, but the distribution of components in the source-oriented model affects calculated optical properties of the atmosphere.

A version of the Source-Oriented WRF/Chem (SOWC) model with 250 m spatial resolution (SOWC-HR) was developed and implemented to perform high resolution simulations over the community of Oakland, California, during March 2010. The HR (250 m) case predicted maximum EC concentrations in Oakland that were nearly 2x greater than concentrations predicted using 1 km resolution. The SOWC-HR model predicted population-weighted maximum hourly EC concentrations that were +9 percent to +32 percent greater than exposures calculated using 1 km resolution.

A version of the SOWC model with warm cloud processes was implemented to study a fog event that occurred on January 17, 2011, in the Central Valley of California. The SOWC model produced more reasonable liquid water path, spatial distribution and duration of fog events compared to the WRF simulation with default prescribed aerosols. The source-oriented mixture representation of particles reduced cloud droplet number and cloud water mass relative to the internal mixture approach that artificially coats hydrophobic particles with hygroscopic components.


Figure 3. The relative change ((internal-source oriented)/source oriented * 100%) in 24-hour averaged (a) cloud water mixing ratio and (b) cloud droplet number on January 17, 2011.

The SOWC model was used to predict the co-benefits of the Global Warming Solutions Act of 2006 (AB32) on reduction of PM concentrations in California during an extreme stagnation event in 2050. Both the San Joaquin Valley (SJV) and the South Coast Air Basin (SoCAB) were predicted to exceed the 24-hour averaged PM2.5 National Ambient Air Quality Standard (NAAQS) of 35 µg m-3 under the business as usual (BAU) emissions scenario during the simulated extreme air pollution event. Implementation of AB32 reduced predicted population-weighted PM2.5concentrations by ~5 percent in California compared to the BAU condition. The source-oriented representation of aerosols increased predicted PM2.5concentrations by ~1-3 percent relative to a version of the model that used the internal mixture approximation. A comparison of SOWC model and off-line air quality model predictions showed that the aerosols feedbacks on meteorology played a significant role in determining future PM2.5concentrations.


Figure 4.  Population-weighted exposure to episode averaged PM2.5, EC, OC, sulfate, nitrate, ammonium, and other in the 4km LA domain and 4km SJV domain predicted by Business as Usual (BAU_E) and AB 32 (AB32_E) simulations in the South Coast Air Basin (LA) and San Joaquin Valley (SJV).

Conclusions:

Measurements indicate that changing climate will have weak direct impacts on emissions from transportation sources in California, but adoption of new fuels and/or technologies to mitigate GHG emissions can have significant impacts on emissions of criteria pollutants. Feedbacks between local air pollution and local meteorology appear to be significant during strong stagnation events in California. Source-oriented models that explicitly predict the mixing state of airborne particles should be used for future downscaling exercises that seek to calculate regional effects of climate change in California.

Future Work:

The emissions measurements for bio-fuels and the source-oriented WRF/Chem (SOWC) model should be applied to predict future air quality in California over a climatologically relevant time period (+40 months spread out over ~10 yrs).  The impact of climate change on air quality in California should be examined over long time periods and during extreme pollution events with appropriate testing for statistical significance. 


Journal Articles on this Report : 6 Displayed | Download in RIS Format

Other project views: All 6 publications 6 publications in selected types All 6 journal articles
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Journal Article Joe DK, Zhang H, DeNero SP, Lee H-H, Chen S-H, McDonald BC, Harley RA, Kleeman MJ. Implementation of a high-resolution Source-Oriented WRF/Chem model at the Port of Oakland. Atmospheric Environment 2014;82:351-363. R833372 (Final)
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  • Journal Article Magara-Gomez KT, Olson MR, Okuda T, Walz KA, Schauer JJ. Sensitivity of hazardous air pollutant emissions to the combustion of blends of petroleum diesel and biodiesel fuel. Atmospheric Environment 2012;50:307-313. R833372 (2011)
    R833372 (Final)
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  • Journal Article Magara-Gomez KT, Olson MR, Okuda T, Walz KA, Schauer JJ. Sensitivity of diesel particulate material emissions and composition to blends of petroleum diesel and biodiesel fuel. Aerosol Science and Technology 2012;46(10):1109-1118. R833372 (2011)
    R833372 (Final)
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  • Journal Article Okuda T, Schauer JJ, Olson MR, Shafer MM, Rutter AP, Walz KA, Morschauser PA. Effects of a platinum-cerium bimetallic fuel additive on the chemical composition of diesel engine exhaust particles. Energy & Fuels 2009;23(10):4974-4980. R833372 (2008)
    R833372 (2009)
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    R833372 (2011)
    R833372 (Final)
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  • Journal Article Zhang H, Magara-Gomez KT, Olson MR, Okuda T, Walz KA, Schauer JJ, Kleeman MJ. Atmospheric impacts of black carbon emission reductions through the strategic use of biodiesel in California. Science of the Total Environment 2015;538:412-422. R833372 (2011)
    R833372 (Final)
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  • Journal Article Zhang H, DeNero SP, Joe DK, Lee H-H, Chen S-H, Michalakes J, Kleeman MJ. Development of a source oriented version of the WRF/Chem model and its application to the California regional PM10/PM2.5 air quality study. Atmospheric Chemistry and Physics 2014;14(1):485-503. R833372 (Final)
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  • Supplemental Keywords:

    Global change, biofuels, aerosol feedbacks;, RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, particulate matter, Air Quality, Air Pollutants, Chemistry, climate change, Air Pollution Effects, Monitoring/Modeling, Atmospheric Sciences, Environmental Engineering, Atmosphere, anthropogenic stress, aerosol formation, ambient aerosol, atmospheric particulate matter, atmospheric dispersion models, environmental monitoring, meteorology, climatic influence, emissions monitoring, future projections, global change, ozone, air quality models, climate models, greenhouse gases, airborne aerosols, atmospheric aerosol particles, atmospheric transport, environmental stress, regional emissions model, ecological models, climate model, greenhouse gas, aerosols, atmospheric models, Global Climate Change, atmospheric chemistry, ambient air pollution

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    Progress and Final Reports:

    Original Abstract
  • 2007 Progress Report
  • 2008 Progress Report
  • 2009 Progress Report
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  • 2011 Progress Report