Final Report: Guiding Future Air Quality Management in California: Sensitivity to Changing Climate

EPA Grant Number: R830964
Title: Guiding Future Air Quality Management in California: Sensitivity to Changing Climate
Investigators: Harley, Robert A. , Cohen, Ronald , Goldstein, Allen H. , Steiner, Allison L , Tonse, Shaheen
Institution: University of California - Berkeley
EPA Project Officer: Chung, Serena
Project Period: March 22, 2003 through March 23, 2006 (Extended to March 22, 2009)
Project Amount: $900,000
RFA: Assessing the Consequences of Global Change for Air Quality: Sensitivity of U.S. Air Quality to Climate Change and Future Global Impacts (2002) RFA Text |  Recipients Lists
Research Category: Global Climate Change , Air Quality and Air Toxics , Climate Change , Air

Objective:

Future air quality will be determined by a combination of technological and societal changes in concert with management of public policy all interacting with changing climate. Historically, policies aimed at reducing the negative impacts of ozone and particles on people and crops have not taken climate change into account. This is largely because there has not been an adequate scientific foundation upon which to estimate the consequences of coupling climate variables to air quality forecasts. In this research, we aimed to lay the scientific groundwork for developing public policy that incorporates the effects of climate change on air quality. The research includes comprehensive analyses of models and observations to assess air quality sensitivity to key climate variables.
 
The overall objective of this research is to assess the impact of changes in regional and global climate on future air quality in California. The results will provide guidance for air quality management. Specifically, we proposed to
 
(1) conduct relevant analyses to improve the understanding of the effects on air quality of climate variables and processes;
(2) quantify sensitivity of tropospheric ozone in California to changes in climatesensitive processes; and
(3) assess uncertainty in predictions of climate-related air quality changes
 
Air Quality Model Description
 
In this research we used the Community Multiscale Air Quality (CMAQ) model, version 4.3. The CMAQ model combines spatially and temporally resolved data on emissions of primary air pollutants such as nitrogen oxides (NOx) and volatile organic compounds (VOC) together with a description of prevailing meteorological conditions and a mechanism describing atmospheric chemical reactions to predict the formation and transport of ozone and other related primary (i.e., directly emitted) and secondary pollutants (i.e., those that form by reactions taking place in the atmosphere). CMAQ is used in this research to predict changes in tropospheric ozone levels resulting from various changes in anthropogenic forcing. The CMAQ model is publicly available and supported by EPA; model formulation and assumptions have been described in a peerreviewed journal article by Byun and Schere (Applied Mechanics Reviews, 2006).
 
Model evaluation activities included comparison of observed and predicted pollutant concentrations for a historical air pollution episode in summer 2000 (Steiner et al., 2006), and more detailed evaluation of the modeled chemical composition and reactivity of volatile organic compounds (VOC) against observations (see Steiner et al., 2008). We also examined the consequences of omitting biogenic emissions of methylbutenol; these emissions from pine trees have typically been ignored in past studies.
 
Key modeling uncertainties in our assessment include the nature and extent of future changes to climate in Central California (we relied on downscaled global climate model results obtained from Snyder et al. (Geophysical Research Letters, 2002) as the basis for our assessment, these correspond to a doubling of atmospheric carbon dioxide relative to pre-industrial levels). Baseline estimates of biogenic and anthropogenic emissions are another well-known source of uncertainty in air quality modeling. The emission estimates that we used were developed using data provided by the California Air Resources Board, as described by Steiner et al. (2006). We also used forecasts of future population growth and technology change in California to estimate future anthropogenic emissions as of 2050. Also the assumed air pollutant levels in Pacific Ocean inflow, especially ozone increases as of 2050, are another source of uncertainty in this assessment.

Summary/Accomplishments (Outputs/Outcomes):

Effects of Climate Change on Air Quality
 
A series of air quality model simulations was performed to examine the individual effects of future climate indicators (including the impact of temperature on chemical kinetics, absolute humidity, and biogenic VOC emissions), and future emissions changes (2050 anthropogenic emissions and changes to concentrations of air pollution at the Pacific Ocean inflow boundary). Additional simulations were performed to examine the effects of the combined climate response and the combined climate and emissions response. A summary of these impacts for three sub-regions of central California (the San Francisco Bay Area, Sacramento, and Fresno) is shown below in Figure 1.
 
Changes in climate variables, including temperature and atmospheric moisture, cause increases in ozone on the order of a few ppb. Climatically influenced biogenic emissions cause ozone increases of a similar magnitude. Other chemical changes, such as the increase of concentrations at the western boundary, can cause greater changes in ozone depending on proximity to the boundary and other geographic features, e.g., the strong impact on the San Francisco Bay area. We predict reductions in anthropogenic emissions by 2050 based on assumptions regarding future technologies and growth, setting an aggressive target for air quality control regulatory policies. These reductions lead to ozone decreases of 10-20 ppb in urban areas and represent the greatest single potential impact on ozone concentrations. NOx reductions of 10-20% are not large enough to be effective at ozone reduction, but VOC and CO emission reductions in NOx-saturated regions are effective at reducing ozone. In fact, because of the nonlinearities in ozone formation, these small NOx reductions likely offset some of the benefit of VOC reductions.
 
 
Figure 1. Weekday 1500LT percent change in maximum ozone concentration, based on spatial averages for three locations: Fresno, Sacramento, and the San Francisco Bay Area. Positive values represent concentrations that are greater in the perturbed case than the base case. The “combined climate” simulation includes the temperature, humidity and biogenic VOC changes. The “climate + emissions” simulation includes temperature, humidity, biogenic VOC, 2050 anthropogenic emissions, and boundary condition changes.
 
When evaluating the combined effects of these perturbations, we find that the overall impact varies greatly by region, with strong correlation to NOx concentrations and proximity to the coastline. This modeling study indicates that regions such as the San Francisco Bay area are more sensitive than others to climate change, and climate change impacts are likely to negate many of the benefits of projected emissions reductions. However in the Central Valley, anthropogenic emissions reductions are predicted to be effective, despite a slight decrease in their efficacy due to climatic changes. These results indicate that the benefits of aggressive emissions reductions will be overstated if climatic changes are not accounted for in projections.
 
Effects of Missing Biogenic Emissions of Methylbutenol (MBO)
 
We conducted the first regional-scale chemistry simulation investigating the effects of biogenic 2-methyl-3-buten-2-ol emissions on air quality. In Central California, MBO emissions have a distinctly different regional pattern than isoprene, but have similar daily maxima of about 5 mg m–2 hr–1. MBO oxidation causes an increase in ozone, formaldehyde, acetone and consequently hydrogen radical production (PHOx). The addition of MBO increases the daily maximum ozone as much as 3 ppb near source regions (2-5% in rural areas) and as much as 1 ppb in the Central Valley. Formaldehyde concentrations increase by as much as 1 ppb (40%) over the Sierra Nevada Mountains, increasing the production of HOx by 10-20% and accelerating local chemistry. This indicates that inclusion of MBO and other biogenic oxygenated emissions in regional simulations in the western and southeastern United States is essential for accurate representation of ozone and HOx.
 
Volatile Organic Compound Reactivity
 
Volatile organic compound (VOC) reactivity in central California was examined using a photochemical air quality model and ground-based measurements to evaluate the contribution of VOC to photochemical activity. We classified VOC into four categories: anthropogenic, biogenic, aldehyde, and other oxygenated VOC. Anthropogenic and biogenic VOC consist of primary emissions, while aldehydes and other oxygenated VOC include both primary anthropogenic emissions and secondary products from primary VOC oxidation. To evaluate the model treatment of VOC chemistry, we compare calculated and modeled OH and VOC reactivities using the following metrics: 1) cumulative distribution functions of NOx concentration and VOC reactivity (ROH,VOC), 2) the relationship between ROH,VOC and NOx, 3) total OH reactivity (ROH,total) and speciated contributions, and 4) the relationship between speciated ROH,VOC and NOx. We find that the model predicts ROH,total to within 25–40% at three sites representing urban (Sacramento), suburban (Granite Bay) and rural (Blodgett Forest) chemistry. However in the urban area of Fresno, the model under predicts NOx and VOC emissions by a factor of 2–3. At all locations the model is consistent with observations of the relative contributions of total VOC. In urban areas, anthropogenic and biogenic ROH,VOC are predicted fairly well over a range of NOx conditions. In suburban and rural locations, anthropogenic and other oxygenated ROH,VOC relationships are reproduced, but calculated biogenic and aldehyde ROH,VOC are often poorly characterized by measurements, making evaluation of the model with available data unreliable. In central California, 30–50% of the modeled urban VOC reactivity is due to aldehydes and other oxygenated species, and the total oxygenated ROH,VOC is nearly equivalent to anthropogenic VOC reactivity. In rural vegetated regions, biogenic and aldehyde reactivity dominates. This indicates that more attention needs to be paid to the accuracy of models and measurements of both primary emissions of oxygenated VOC and secondary production of oxygenates, especially formaldehyde and other aldehydes, and that a more comprehensive set of oxygenated VOC measurements is required to include all of the important contributions to atmospheric reactivity.
 
Temperature Dependence of NOy Speciation
 
We presented and analyzed observations of atmospheric reactive nitrogen compounds including NO, NO2, total peroxy nitrates, total alkyl nitrates, and HNO3 and their correlation with temperature. The measurements were made at a rural location 1315 m above sea level on the western slope of the Sierra Nevada Mountains in California during summer of 2001. The ratio of HNO3 to its source molecule, NO2, and the ratio of HNO3 to all other higher oxides of nitrogen (NOz) both increase with increasing temperature. Analysis of these increases suggests they are due to a steep increase in OH of between a factor of 2 and 3 over the range 18–32°C. Total peroxy nitrates decrease and total alkyl nitrates increase over the same temperature range. The decrease in the total peroxy nitrates is shown to be much less than expected if the rate of thermal decomposition were the sole important factor. This observation is consistent with the increase in OH inferred from the temperature trends in the HNO3/NO2 ratio.
 
Temperature and Seasonal Effects on Anthropogenic VOC Emissions
 
A chemical mass balance approach was used to determine the relative contributions of evaporative versus tailpipe sources to motor vehicle volatile organic compound (VOC) emissions. Contributions were determined by reconciling time-resolved ambient VOC concentrations measured downwind of Sacramento, California, in summer 2001 with source speciation profiles. A composite liquid fuel speciation profile was determined from gasoline samples collected at Sacramento area service stations. Vapor-liquid equilibrium relationships were used to determine the corresponding headspace vapor composition. VOC concentrations measured in a highway tunnel were used to define the composition of running vehicle emissions. The chemical mass balance analysis indicated that headspace vapor contributions ranged from 7 to 29% of total vehicle-related VOC depending on time of day and day of week, with a mean daytime contribution of 17.0 ±0.9% (mean ± 95% CI). A positive association between the headspace vapor contribution and ambient air temperature was found for afternoon hours. We estimate a 6.5 ± 2.5% increase in vapor pressure-driven evaporative emissions and at least a 1.3 ± 0.4% increase in daily total (exhaust plus evaporative) VOC emissions from motor vehicles per degree Celsius increase in maximum temperature.
 
On- and off-road mobile sources are the dominant contributors to urban anthropogenic volatile organic compound (AVOC) emissions. Analyses of gasoline samples from California for both summer and winter indicate significant differences in liquid fuel and vapor chemical composition due to intentional seasonal adjustments. Ambient concentrations of 55 VOCs were measured via in situ gas chromatography in the 2005 Study of Organic Aerosols at Riverside (SOAR) during both summer and fall. A chemical mass balance analysis was used to differentiate vapor pressure-driven VOC emissions from other motor vehicle-related emissions such as tailpipe exhaust. Overall, fuel vapor emissions accounted for 31 ± 2% of gasoline-related VOC in Riverside; California’s emission factor model similarly estimates 31% of gasoline-related VOC emissions are fuel vapor. The diurnal pattern of vapor pressure-driven VOC source contributions is relatively stable around 10 μg/m3, while whole gasoline (i.e., tailpipe) contributions peak at ∼60 μg/m3 during the morning commute. There is no peak in whole gasoline source contributions during the afternoon, due to rapid dilution associated with high mixing heights and wind speeds in the Riverside area. The relationship between estimated gasoline-related VOC and observed carbon monoxide concentrations in this study is similar to California’s 2005 emission inventory; we calculated a VOC to CO mass ratio of 0.086±0.006 (95% CI) compared to 0.097 in the emission inventory for all gasoline-related sources.

Conclusions:

California already suffers from poor ozone air quality, and we found that climate change could make matters worse, by increasing the amount of emission control needed to meet health-based air quality standards in the future. Climate change impacts (here we refer mainly to the effect of increased temperatures on atmospheric chemistry and biogenic VOC emission rates) were large enough in some locations to offset fully the impacts of current emission control programs.
 
A variety of oxygenated VOC, some emitted naturally by vegetation, others formed in the atmosphere by chemical reactions, are more important than can be explained by current emission inventories and models. Further efforts are needed to include the oxygenated VOC in field measurement, emission inventory, and modeling studies.
 
Some anthropogenic VOC emissions depend on temperature, for example because the vapor pressure of gasoline increases exponentially with temperature. Our analyses of ambient VOC concentrations measured in special studies indicate, however, that tailpipe rather than evaporative modes are the dominant source of gasoline-related VOC emissions in California.
 
Correlations of measured pollutant concentrations with ambient temperature suggest strong associations between air pollution and climate change. Temperature is, however, only one of many inter-related meteorological variables. Further research is needed to explore the explicit and implicit dependencies of air pollution on temperature. For example, hotter days also tend to be more stagnant so transport patterns differ; biogenic and anthropogenic VOC emissions may increase on hotter days; the chemical distribution of NOy among its various forms is affected by increased HOx radical production at higher temperatures.


Journal Articles on this Report : 8 Displayed | Download in RIS Format

Other project views: All 27 publications 8 publications in selected types All 8 journal articles
Type Citation Project Document Sources
Journal Article Day DA, Wooldridge PJ, Cohen RC. Observations of the effects of temperature on atmospheric HNO3, ΣANs, ΣPNs, and NOx: evidence for a temperature-dependent HOx source. Atmospheric Chemistry and Physics 2008;8(6):1867-1879. R830964 (2007)
R830964 (Final)
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  • Journal Article Gentner DR, Harley RA, Miller AM, Goldstein AH. Diurnal and seasonal variability of gasoline-related volatile organic compound emissions in Riverside, California. Environmental Science & Technology 2009;43(12):4247-4252. R830964 (Final)
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  • Journal Article Millstein DE, Harley RA. Impact of climate change on photochemical air pollution in southern California. Atmospheric Chemistry and Physics Discussions 2009;9(1):1561-1583. R830964 (Final)
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  • Journal Article Rubin JI, Kean AJ, Harley RA, Millet DB, Goldstein AH. Temperature dependence of volatile organic compound evaporative emissions from motor vehicles. Journal of Geophysical Research--Atmospheres 2006;111(D3):D03305 (7 pp.). R830964 (2005)
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  • Journal Article Steiner AL, Tonse S, Cohen RC, Goldstein AH, Harley RA. Influence of future climate and emissions on regional air quality in California. Journal of Geophysical Research--Atmospheres2006;111(D18):D18303 (22 pp.). R830964 (2006)
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  • Journal Article Steiner AL, Tonse S, Cohen RC, Goldstein AH, Harley RA. Biogenic 2-methyl-3-buten-2-ol increases regional ozone and HOx sources. Geophysical Research Letters 2007;34(15):L15806 (6 pp.). R830964 (2006)
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  • Journal Article Steiner AL, Cohen RC, Harley RA, Tonse S, Millet DB, Schade GW, Goldstein AH. VOC reactivity in central California: comparing an air quality model to ground-based measurements. Atmospheric Chemistry and Physics 2008;8(2):351-368. R830964 (2007)
    R830964 (Final)
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  • Journal Article Weaver CP, Liang X-Z, Zhu J, Adams PJ, Amar P, Avise J, Caughey M, Chen J, Cohen RC, Cooter E, Dawson JP, Gilliam R, Gilliland A, Goldstein AH, Grambsch A, Grano D, Guenther A, Gustafson WI, Harley RA, He S, Hemming B, Hogrefe C, Huang H-C, Hunt SW, Jacob DJ, Kinney PL, Kunkel K, Lamarque J-F, Lamb B, Larkin NK, Leung LR, Liao K-J, Lin J-T, Lynn BH, Manomaiphiboon K, Mass C, McKenzie D, Mickley LJ, O'neill SM, Nolte C, Pandis SN, Racherla PN, Rosenzweig C, Russell AG, Salathe E, Steiner AL, Tagaris E, Tao Z, Tonse S, Wiedinmyer C, Williams A, Winner DA, Woo J-H, Wu S, Wuebbles DJ. A preliminary synthesis of modeled climate change impacts on U.S. regional ozone concentrations. Bulletin of the American Meteorological Society 2009;90(12):1843-1863. R830964 (Final)
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  • Supplemental Keywords:

    RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, particulate matter, Air Quality, Air Pollutants, Chemistry, climate change, Air Pollution Effects, Monitoring/Modeling, Environmental Monitoring, tropospheric ozone, Atmospheric Sciences, Atmosphere, anthropogenic stress, aerosol formation, ambient aerosol, atmospheric particulate matter, atmospheric dispersion models, environmental measurement, meteorology, climatic influence, global change, ozone, air quality models, climate, air pollution models, air quality model, air sampling, climate models, greenhouse gases, airborne aerosols, atmospheric aerosol particles, atmospheric transport, biogenic ozone precursors, environmental stress, atmospheric monitoring, ecological models, California, aerosols, atmospheric models, Global Climate Change, atmospheric chemistry, ambient air pollution

    Progress and Final Reports:

    Original Abstract
  • 2003 Progress Report
  • 2004 Progress Report
  • 2005 Progress Report
  • 2006 Progress Report
  • 2007 Progress Report