Final Report: Impact of Climate Change on Air Quality in the U.S.: Investigations With Linked Global- and Regional-Scale Models

EPA Grant Number: R833377
Title: Impact of Climate Change on Air Quality in the U.S.: Investigations With Linked Global- and Regional-Scale Models
Investigators: Sillman, Sanford , Keeler, Gerald J. , Penner, Joyce
Institution: University of Michigan
EPA Project Officer: Hunt, Sherri
Project Period: February 1, 2007 through January 31, 2010 (Extended to January 31, 2012)
Project Amount: $899,468
RFA: Consequences of Global Change For Air Quality (2006) RFA Text |  Recipients Lists
Research Category: Global Climate Change , Climate Change , Air


The initial goal of the project was to investigate the impact of future climate and emissions on air quality in the U.S., with focus on ozone and mercury. The project planned to use models that include gas-phase and aqueous photochemistry and an updated representation of the interaction between aerosols and tropospheric chemistry as a basis for investigating the climate-air quality interaction.

A major focus was observation-based methods – an attempt to identify atmospheric measurements that can be used to estimate the impact of climate change and global increases in emissions on air quality. The best example of this is the observed correlation between ozone and temperature. This correlation has been used to evaluate long-term changes in ozone air quality with the effect of year-to-year climate variations filtered out (e.g. Fiore et al., 1998). It has also been used to estimate the ‘climate penalty’ in terms of ozone air quality that would result from warmer temperatures (Bloomer et al., 2009). Another is the correlation between ozone and NOx reaction products (NOy-NOx, or NOz). The slope between O3 and NOz has been associated with the “ozone production efficiency per emitted NOx," which estimates the added ozone burden per emitted NOx (Trainer et al., 1993). The O3-NOz correlation has also been used to distinguish VOC-sensitive and NOx-sensitive conditions for ozone production (e.g. Sillman and He, 2002).

In the course of work the project focused shifted more to focus on the role of secondary organic aerosols (SOA) in association with air quality, their mechanism of formation and their interaction with climate. SOA formation became a focus because measurements identified SOA to account for a significant fraction of aerosol content, which could not be explained by current formation mechanisms. We have added alternative mechanisms for formation of SOA in global-scale models and used them to evaluate possible SOA formation pathways along with their implication for air quality and climate.


Summary/Accomplishments (Outputs/Outcomes):

Revised understanding of the relation between ozone and temperature: Global-scale photochemical models were evaluated in comparison with the observed correlation of ozone and reactive nitrogen species (PAN, HNO3) with temperature. Results provide a level of confidence in model ability to predict changes in atmospheric composition and photochemistry in response to future-year temperature increases. Models predict that future-year ozone will increase as the temperature increases, matching the observed correlation with ozone with temperature. However, global background O3 is not predicted to increase with temperature and actually decreases very slightly in response to a temperature increase.

Methods to identify the impact of intercontinental transport: The effect of intercontinental transport on O3 in the U.S. is attributed just 50% to direct transport of O3 and 50% to transport of ozone precursors, including PAN and HNO3. Episodic transport of O3 is associated with unusually steep slopes of O3 versus CO and O3 versus PAN. However, the global impact on general background levels of O3 is likely to be more important than the noticeable transport episodes. The increase in global background O3 is likely to affect median O3 more than peak O3.

Technical improvements in models for atmospheric mercury: A recent version of the Community Model for Air Quality (CMAQ Version 4.7.1, released in 2010) was found to have various technical problems that prevented the model from running. Technical corrections were made and posted for public use.

Expansion to include secondary organic aerosols: A significant expansion of the capability of chemistry/transport models was made by adding explicit representation of the photochemical formation of secondary organic aerosols. The expansion included the following SOA formation pathways: (i) direct photochemical pathways developed here, formation from glyoxal and methyl glyoxal (Fu et al., 2008); (ii) formation from epoxides derived from isoprene (Paulot et al., 2009); and (iii) possible formation based on hydroxy acetone (Ervens et al., 2008, Matsunaga et al., 2004).

Evaluation of the effect of SOA reaction pathways on climate: Results from global-scale modeling suggests that significant SOA was present for pre-industrial conditions. Anthropogenic aerosols have a net cooling impact on climate, but this impact is much smaller if SOA are included (-1.2 W/m2 vs. -1.9 W/m2). SOA represents one of the major uncertainties for climate forecasts, and this modification may affect interpretation of how and why climate has changed over the past century and projections for the future.

Sensitivity of SOA formation to NOx and VOC: Photochemical formation shows a complex dependence to NOx and VOC precursors with NOx-sensitive and VOC-sensitive regimes, somewhat comparable to ozone formation. In contrast to ozone, VOC-sensitive chemistry can occur at very low NOx, and conditions are VOC-sensitive for NOx above 0.1 ppb. 


  • The observed ozone increase with temperature is generally consistent with representations in photochemical models, but is critically dependent on assumptions about the chemistry of isoprene nitrates.
  • Changes in background O3 and transport of pollutants to the US might be identified based on changes in the observed correlation between ozone and peroxyacetyl nitrates (PANs).
  • Recent proposed photochemical pathways for production of secondary organic aerosols (SOA) enable global-scale models to generate enough ambient SOA to come close to matching measured values. The reaction pathway from isoprene through epoxides is especially important.
  • When SOA is included in climate models, it significantly changes model predictions for present-day versus pre-industrial climate. SOA has a significant cooling effect on climate, but new reaction pathways imply that the increase in SOA since preindustrial times was smaller than previously thought.


Bloomer B, Stehr J, Piety C, Salawitch R, Dickerson R. Observed relationships of ozone air pollution with temperature and emissions. Geophysical Research Letters 2009;36:L09803, doi:10.1029/2009GL037308.

Ervens B, Volkamer R. Glyoxal processing by aerosol multiphase chemistry: towards a kinetic modeling framework of secondary organic aerosol formation in aqueous particles. Atmospheric Chemistry and Physics 2010;10:8219-8244.

Fiore AM, Jacob DJ, Logan JA, Yin JH, Long-term trends in ground level ozone over the contiguous United States, 1980-1995. Journal of Geophysical Research 1998;103:1471-1480.

Fu TM, Jacob DJ, Wittrock F, Burrows JP, Vrekoussis M, Henze DK. Global budgets of atmospheric glyoxal and methylglyoxal, and implications for formation of secondary organic aerosols. Journal of Geophysical Research 2008;113:D15303, doi:10.1029/2007JD009505,2008.

Paulot F, Crounse JD, Kjaergaard HG, Kurten A, St. Clair JM, Seinfeld JH, Wennberg PO. Unexpected epoxide formation in the gas-phase photooxidation of isoprene. Science 2009;325:730-733.

Sillman S, He D. Some theoretical results concerning O3-NOx-VOC chemistry and NOx-VOC indicators. Journal of Geophysical Research 2002;107(D22):4659, doi:10.1029/2001JD001123.

Trainer M, Parrish DD, Buhr MP, Norton RB, Fehsenfeld FC, Anlauf KG, Bottenheim JW, Tang YZ, Wiebe HA, Roberts JM, Tanner RL, Newman L, Bowersox VC, Maugher JM, Olszyna KJ, Rodgers MO, Wang T, Berresheim H, and Demerjian K. Correlation of ozone with NOy in photochemically aged air. Journal of Geophysical Research 1993;98:2917-2926.

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

Other project views: All 15 publications 6 publications in selected types All 6 journal articles
Type Citation Project Document Sources
Journal Article Ito A, Sillman S, Penner JE. Global chemical transport model study of ozone response to changes in chemical kinetics and biogenic volatile organic compounds emissions due to increasing temperatures:sensitivities to isoprene nitrate chemistry and grid resolution. Journal of Geophysical Research 2009;114(D9):D09301 (19 pp.). R833377 (2009)
R833377 (2010)
R833377 (Final)
  • Full-text: Wiley-Full Text PDF
  • Abstract: Wiley-Abstract
  • Journal Article Lin GX, Penner JE, Sillman S, Taraborrelli D, Lelieveld J. Global modeling of SOA formation from dicarbonyls, epoxides, organic nitrates and peroxides. Atmospheric Chemistry and Physics 2012;12(10):4743-4774. R833377 (Final)
  • Full-text: ACP-Full-text PDF
  • Abstract: ACP-Abstract & Full-text HTML
  • Journal Article Lin GX, Penner JE, Flanner MG, Sillman S, Xu L, Zhou C. Radiative forcing of organic aerosol in the atmosphere and on snow:Effects of SOA and brown carbon. Journal of Geophysical Research-Atmospheres 2014;119(12):7453-7476. R833377 (Final)
  • Full-text: Wiley-Full Text PDF
  • Abstract: Wiley-Abstract & Full Text HTML
  • Journal Article Lin GX, Sillman S, Penner JE, Ito A. Global modeling of SOA:the use of different mechanisms for aqueous phase formation. Atmospheric Chemistry and Physics 2014;14(11):5451-5475. R833377 (Final)
  • Full-text: ACP-Full Text PDF
  • Abstract: ACP-Abstract & Full-text HTML
  • Journal Article Steiner AL, Davis AJ, Sillman S, Owen RC, Michalak AM, Fiore AM. Observed suppression of ozone formation at extremely high temperatures due to chemical and biophysical feedbacks. Proceedings of the National Academy of Sciences of the United States of America 2010;107(46):19685-19690. R833377 (2010)
    R833377 (Final)
  • Full-text from PubMed
  • Abstract from PubMed
  • Associated PubMed link
  • Full-text: PNAS-Full Text PDF
  • Abstract: PNAS-Abstract & Full Text HTML
  • Journal Article Tsigaridis K, Daskalakis N, Kanakidou M Adams PJ, Artaxo P, Bahadur R, Balkanski Y, Bauer SE, Bellouin N, Benedetti A, Bergman T, Berntsen TK, Beukes JP, Bian H, Carslaw KS, Chin M, Curci G, Diehl T, Easter RC, Ghan SJ, Gong SL, Hodzic A, Hoyle CR, Iversen T, Jathar S, Jimenez JL, Kaiser JW, Kirkevag A, Kochb D, Kokkola H, Leec YH, Lin G, Liu X, Luo G, Ma X, Mann GW, Mihalopoulos N, MorcretteJ-J, Muller J-F, Myhre G, Myriokefalitakis S, Ng NL, O'Donnell D, Penner JE, Pozzoli L, Pringle KJ, Russell LM, Schulz M, Sciare J, Seland O, Shindell DT, Sillman S, Skeie RB, Spracklen D, Stavrakou T, Steenrod SD, Takemura T, Tiitta P, Tilmes S, Tost H, van Noije T, van Zyl PG, von Salzen K, Yu F, Wang Z, Wang Z, Zaveri RA, Zhang H, Zhang K, Zhang Q, Zhang X. The AeroCom evaluation and intercomparison of organic aerosol in global models. Atmospheric Chemistry and Physics 2014;14(19):10845-10895. R833377 (Final)
  • Full-text: ACP-Full Text PDF
  • Abstract: ACP-Abstract
  • Supplemental Keywords:

    RFA, Air, climate change, Air Pollution Effects, Atmosphere

    Relevant Websites:

    Observation-based methods (OBMs) for analyzing urban/regional ozone production and Ozone-NOx-VOC sensitivity | Dr. Sanford Sillman Exit
    Corrections to the Community Multiscale Air Quality (CMAQ) model version 4.7.1 | Dr. Sanford Sillman Exit

    Progress and Final Reports:

    Original Abstract
  • 2007 Progress Report
  • 2008 Progress Report
  • 2009 Progress Report
  • 2010 Progress Report