The rural/remote IMPROVE network (Interagency Monitoring of Protected Visual Environments) and the Environmental Protection Agency's urban Chemical Speciation Network have measured PM2.5 organic (OC) and elemental carbon (EC) since 1989 and 2000, respectively. We aggregated OC and EC data from 2007 to 2010 at over 300 sites from both networks in order to characterize the spatial and seasonal patterns in rural and urban carbonaceous aerosols. The spatial extent of OC and EC was more regional in the eastern United States relative to more localized concentrations in the West. The highest urban impacts of OC and EC relative to background concentrations occurred in the West during fall and winter. Urban and rural carbonaceous aerosols experienced a large (although opposite) range in seasonality in the West compared to a much lower seasonal variability in the East. Long-term (1990–2010) trend analyses indicated a widespread decrease in rural TC (TC = OC + EC) across the country, with positive, though insignificant, trends in the summer and fall in the West. Short-term trends indicated that urban and rural TC concentrations have both decreased since 2000, with the strongest and more spatially homogeneous urban and rural trends in the West relative to the East. 1. Introduction Carbonaceous aerosols, including organic (OC) and elemental (EC) carbon, are ubiquitous in the atmosphere and therefore contribute significantly to particulate matter, both the PM2.5 fraction [1] and coarse (PM10？PM2.5) fraction [2, 3], and they contribute to visibility degradation [4, 5] and climate forcing due to their ability to scatter and absorb solar radiation [6, 7]. Carbonaceous aerosols also adversely affect health [8, 9]. Organic carbon can be emitted directly from combustion activities or produced from secondary processes such as gas-to-particle formation. Elemental carbon, also known as light absorbing carbon or black carbon depending on the measurement method, is emitted directly from combustion sources. EC plays a significant role in climate forcing, and a recent review [10] suggests that the climate warming effects of EC are greater than previously thought, although large uncertainties still exist. Characterizing and predicting the complex nature of OC and EC are challenging from both a measurement and modeling framework. However, this characterization is necessary given the importance of OC and EC to many atmospheric processes and climate impacts. Comprehensive speciation of carbonaceous aerosols is expensive and time-consuming and therefore usually possible only at a
References
[1]
J. L. Hand, B. A. Schichtel, M. Pitchford, W. C. Malm, and N. H. Frank, “Seasonal composition of remote and urban fine particulate matter in the United States,” Journal of Geophysical Research, vol. 117, no. 5, Article ID D05209, 2012.
[2]
W. C. Malm, M. L. Pitchford, C. McDade, and L. L. Ashbaugh, “Coarse particle speciation at selected locations in the rural continental United States,” Atmospheric Environment, vol. 41, no. 10, pp. 2225–2239, 2007.
[3]
E. S. Edgerton, G. S. Casuccio, R. D. Saylor et al., “Measurements of OC and EC in coarse particulate matter in the southeastern United States,” Journal of the Air & Waste Management Association, vol. 59, no. 1, pp. 78–90, 2009.
[4]
G. R. McMeeking, S. M. Kreidenweis, M. Lunden et al., “Smoke-impacted regional haze in California during the summer of 2002,” Agricultural and Forest Meteorology, vol. 137, no. 1-2, pp. 25–42, 2006.
[5]
J. L. Hand, S. A. Copeland, D. E. Day et al., “IMPROVE (Interagency Monitoring of Protected Visual Environments): spatial and seasonal patterns and temporal variability of haze and its constituents in the United States,” CIRA Report 5, 2011, http://vista.cira.colostate.edu/improve/Publications/Reports/2011/2011.htm.
[6]
T. C. Bond and R. W. Bergstrom, “Light absorption by carbonaceous particles: an investigative review,” Aerosol Science and Technology, vol. 40, no. 1, pp. 27–67, 2006.
[7]
A. H. Goldstein, C. D. Koven, C. L. Heald, and I. Y. Fung, “Biogenic carbon and anthropogenic pollutants combine to form a cooling haze over the southeastern United States,” Proceedings of the National Academy of Sciences of the United States of America, vol. 106, no. 22, pp. 8835–8840, 2009.
[8]
J. L. Mauderly and J. C. Chow, “Health effects of organic aerosols,” Inhalation Toxicology, vol. 20, no. 3, pp. 257–288, 2008.
[9]
A. C. Rohr and R. E. Wyzga, “Attributing health effects to individual particulate matter constituents,” Atmospheric Environment, vol. 62, pp. 130–152, 2012.
[10]
T. C. Bond, S. J. Doherty, D. W. Fahey, et al., “Bounding the role of black carbon in the climate system: a scientific assessment,” Journal of Geophysical Research, vol. 118, no. 11, pp. 5380–5552, 2013.
[11]
R. A. Zaveri, W. J. Shaw, D. J. Cziczo, et al., “Overview of the 2010 Carbonaceous Aerosols and Radiative Effects Study (CARES),” Atmospheric Chemistry and Physics, vol. 12, pp. 7647–7687, 2012.
[12]
W. C. Malm, J. F. Sisler, D. Huffman, R. A. Eldred, and T. A. Cahill, “Spatial and seasonal trends in particle concentration and optical extinction in the United States,” Journal of Geophysical Research, vol. 99, no. 1, pp. 1347–1370, 1994.
D. A. Hansen, E. S. Edgerton, B. E. Hartsell et al., “The Southeastern Aerosol Research and Characterization Study: part 1—overview,” Journal of the Air & Waste Management Association, vol. 53, no. 12, pp. 1460–1471, 2003.
[15]
C. L. Blanchard, G. M. Hidy, S. Tanenbaum, and E. S. Edgerton, “NMOC, ozone, and organic aerosol in the southeastern United States, 1999–2007: 3. Origins of organic aerosol in Atlanta, Georgia, and surrounding areas,” Atmospheric Environment, vol. 45, no. 6, pp. 1291–1302, 2011.
[16]
C. L. Blanchard, G. M. Hidy, S. Tanenbaum, E. S. Edgerton, and B. E. Hartsell, “The Southeastern Aerosol Research and Characterization (SEARCH) Study: temporal trends in gas and PM concentrations and composition, 1999–2010,” Journal of the Air & Waste Management Association, vol. 63, no. 3, pp. 247–259, 2013.
[17]
J. C. Chow, J. G. Watson, L. W. A. Chen, W. P. Arnott, H. Moosmüller, and K. Fung, “Equivalence of elemental carbon by thermal/optical reflectance and transmittance with different temperature protocols,” Environmental Science and Technology, vol. 38, no. 16, pp. 4414–4422, 2004.
[18]
J. C. Chow, J. G. Watson, L.-W. A. Chen, J. Rice, and N. H. Frank, “Quantification of PM2.5 organic carbon sampling artifacts in US networks,” Atmospheric Chemistry and Physics, vol. 10, no. 12, pp. 5223–5239, 2010.
[19]
Y. Cheng, K.-B. He, F.-K. Duan et al., “Ambient organic carbon to elemental carbon ratios: influences of the measurement methods and implications,” Atmospheric Environment, vol. 45, no. 12, pp. 2060–2066, 2011.
[20]
B. Khan, M. D. Hays, C. Geron, and J. Jetter, “Differences in the OC/EC ratios that characterize ambient and source aerosols due to thermal-optical analysis,” Aerosol Science and Technology, vol. 46, no. 2, pp. 127–137, 2012.
[21]
O. V. Rattigan, H. D. Felton, M.-S. Bae, J. J. Schwab, and K. L. Demerjian, “Comparison of long-term PM2.5 carbon measurements at an urban and rural location in New York,” Atmospheric Environment, vol. 45, no. 19, pp. 3228–3236, 2011.
[22]
W. C. Malm, B. A. Schichtel, and M. L. Pitchford, “Uncertainties in PM2.5 gravimetric and speciation measurements and what we can learn from them,” Journal of the Air & Waste Management Association, vol. 61, no. 11, pp. 1131–1149, 2011.
[23]
D. Jaffe, W. Hafner, D. Chand, A. Westerling, and D. Spracklen, “Interannual variations in PM2.5 due to wildfires in the western United States,” Environmental Science and Technology, vol. 42, no. 8, pp. 2812–2818, 2008.
[24]
W. C. Malm, B. A. Schichtel, M. L. Pitchford, L. L. Ashbaugh, and R. A. Eldred, “Spatial and monthly trends in speciated fine particle concentration in the United States,” Journal of Geophysical Research, vol. 109, no. 3, Article ID D03306, 2004.
[25]
B. A. Schichtel, W. C. Malm, G. Bench et al., “Fossil and contemporary fine particulate carbon fractions at 12 rural and urban sites in the United States,” Journal of Geophysical Research, vol. 113, no. 2, Article ID D02311, 2008.
[26]
B. A. Schichtel, M. A. Rodriguez, M. G. Barna, K. A. Gebhart, M. L. Pitchford, and W. C. Malm, “A semi-empirical, receptor-oriented Lagrangian model for simulating fine particulate carbon at rural sites,” Atmospheric Environment, vol. 61, pp. 361–370, 2012.
[27]
L.-W. A. Chen, J. G. Watson, J. C. Chow, D. W. DuBois, and L. Herschberger, “Chemical mass balance source apportionment for combined PM2.5 measurements from U.S. non-urban and urban long-term networks,” Atmospheric Environment, vol. 44, no. 38, pp. 4908–4918, 2010.
[28]
B. Buzcu-Guven, S. G. Brown, A. Frankel, H. R. Hafner, and P. T. Roberts, “Analysis and apportionment of organic carbon and fine particulate matter sources at multiple sites in the midwestern United States,” Journal of the Air & Waste Management Association, vol. 57, no. 5, pp. 606–619, 2007.
[29]
S. Yu, R. L. Dennis, P. V. Bhave, and B. K. Eder, “Primary and secondary organic aerosols over the United States: estimates on the basis of observed organic carbon (OC) and elemental carbon (EC), and air quality modeled primary OC/EC ratios,” Atmospheric Environment, vol. 38, no. 31, pp. 5257–5268, 2004.
[30]
A. Hecobian, X. Zhang, M. Zheng, N. Frank, E. S. Edgerton, and R. J. Weber, “Water-soluble organic aerosol material and the light-absorption characteristics of aqueous extracts measured over the southeastern United States,” Atmospheric Chemistry and Physics, vol. 10, no. 13, pp. 5965–5977, 2010.
[31]
X. Zhang, Z. Liu, A. Hecobian et al., “Spatial and seasonal variations of fine particulate water-soluble organic carbon (WSOC) over the southeastern United States: implications for secondary organic aerosol formation,” Atmospheric Chemistry and Physics, vol. 12, pp. 6593–6607, 2012.
[32]
M. Chin, T. Diehl, P. Ginoux, and W. Malm, “Intercontinental transport of pollution and dust aerosols: implications for regional air quality,” Atmospheric Chemistry and Physics, vol. 7, no. 21, pp. 5501–5517, 2007.
[33]
R. J. Park, D. J. Jacob, M. Chin, and R. V. Martin, “Sources of carbonaceous aerosols over the United States and implications for natural visibility,” Journal of Geophysical Research, vol. 108, no. 12, article 4355, 2003.
[34]
R. J. Park, D. J. Jacob, N. Kumar, and R. M. Yantosca, “Regional visibility statistics in the United States: natural and transboundary pollution influences, and implications for the Regional Haze Rule,” Atmospheric Environment, vol. 40, no. 28, pp. 5405–5423, 2006.
[35]
H. Liao, D. K. Henze, J. H. Seinfeld, S. Wu, and L. J. Mickley, “Biogenic secondary organic aerosol over the United States: comparison of climatological simulations with observations,” Journal of Geophysical Research, vol. 112, no. 6, Article ID D06201, 2007.
[36]
E. Drury, D. J. Jacob, R. J. D. Spurr et al., “Synthesis of satellite (MODIS), aircraft (ICARTT), and surface (IMPROVE, EPA-AQS, AERONET) aerosol observations over eastern North America to improve MODIS aerosol retrievals and constrain surface aerosol concentrations and sources,” Journal of Geophysical Research, vol. 115, no. 14, Article ID D14204, 2010.
[37]
Y. H. Mao, Q. B. Li, L. Zhang et al., “Biomass burning contribution to black carbon in the western United States mountain ranges,” Atmospheric Chemistry and Physics, vol. 11, no. 21, pp. 11253–11266, 2011.
[38]
M. Huang, G. R. Carmichael, S. Kulkarni et al., “Sectoral and geographical contributions to summertime continental United States (CONUS) black carbon spatial distributions,” Atmospheric Environment, vol. 51, pp. 165–174, 2012.
[39]
M. Kanakidou, J. H. Seinfeld, S. N. Pandis et al., “Organic aerosol and global climate modelling: a review,” Atmospheric Chemistry and Physics, vol. 5, no. 4, pp. 1053–1123, 2005.
[40]
X. Liu, R. C. Easter, S. J. Ghan et al., “Toward a minimal representation of aerosols in climate models: description and evaluation in the Community Atmosphere Model CAM5,” Geoscientific Model Development, vol. 5, pp. 709–739, 2012.
[41]
D. M. Murphy, J. C. Chow, E. M. Leibensperger et al., “Decreases in elemental carbon and fine particle mass in the United States,” Atmospheric Chemistry and Physics, vol. 11, no. 10, pp. 4679–4686, 2011.
[42]
L. W. A. Chen, J. C. Chow, J. G. Watson, and B. A. Schichtel, “Consistency of long-term elemental carbon trends from thermal and optical measurements in the IMPROVE network,” Atmospheric Measurement Techniques, vol. 5, pp. 2329–2338, 2012.
[43]
J. C. Chow, J. G. Watson, L. C. Pritchett, W. R. Pierson, C. A. Frazier, and R. G. Purcell, “The DRI thermal/optical reflectance carbon analysis system: description, evaluation and applications in U.S. Air quality studies,” Atmospheric Environment, vol. 27A, no. 8, pp. 1185–1201, 1993.
[44]
J. G. Watson, J. C. Chow, L.-W. A. Chen, and N. H. Frank, “Methods to assess carbonaceous aerosol sampling artifacts for IMPROVE and other long-term networks,” Journal of the Air & Waste Management Association, vol. 59, no. 8, pp. 898–911, 2009.
[45]
A. M. Dillner, C. H. Phuah, and J. R. Turner, “Effects of post-sampling conditions on ambient carbon aerosol filter measurements,” Atmospheric Environment, vol. 43, no. 37, pp. 5937–5943, 2009.
[46]
J. L. Hand, W. C. Malm, A. Laskin et al., “Optical, physical, and chemical properties of tar balls observed during the Yosemite Aerosol Characterization Study,” Journal of Geophysical Research, vol. 110, no. 21, Article ID D21210, pp. 1–14, 2005.
“CSN data,” http://views.cira.colostate.edu/fed/ or http://www.epa.gov/ttn/airs/airsaqs/.
[49]
B. J. Turpin and H.-J. Lim, “Species contributions to PM2.5 mass concentrations: revisiting common assumptions for estimating organic mass,” Aerosol Science and Technology, vol. 35, no. 1, pp. 602–610, 2001.
[50]
H. Theil, “A rank-invariant method of linear and polynomial regression analysis I,” in Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen, vol. A53, pp. 386–392, 1950.
[51]
H. Theil, “A rank-invariant method of linear and polynomial regression analysis II,” in Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen, vol. A53, pp. 521–525, 1950.
[52]
H. Theil, “A rank-invariant method of linear and polynomial regression analysis III,” in Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen, vol. A53, pp. 1397–1412, 1950.
[53]
D. V. Spracklen, J. A. Logan, L. J. Mickley et al., “Wildfires drive interannual variability of organic carbon aerosol in the western U.S. in summer,” Geophysical Research Letters, vol. 34, no. 16, Article ID L16816, 2007.
[54]
A. S. Holden, A. P. Sullivan, L. A. Munchak et al., “Determining contributions of biomass burning and other sources to fine particle contemporary carbon in the western United States,” Atmospheric Environment, vol. 45, no. 11, pp. 1986–1993, 2011.
[55]
J. C. Chow, L.-W. A. Chen, J. G. Watson et al., “PM2.5 chemical composition and spatiotemporal variability during the Californian Regional PM10/PM2.5 Air Quality Study (CRPAQS),” Journal of Geophysical Research, vol. 111, no. 10, Article ID D10S04, 2006.
[56]
S. A. Christopher, P. Gupta, U. Nair et al., “Satellite remote sensing and mesoscale modeling of the 2007 Georgia/Florida fires,” IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, vol. 2, no. 3, pp. 163–175, 2009.
[57]
X. Zhang, A. Hecobian, M. Zheng, N. H. Frank, and R. J. Weber, “Biomass burning impact on PM2.5 over the southeastern US during 2007: integrating chemically speciated FRM filter measurements, MODIS fire counts and PMF analysis,” Atmospheric Chemistry and Physics, vol. 10, no. 14, pp. 6839–6853, 2010.
[58]
G. Bench, S. Fallon, B. Schichtel, W. Malm, and C. McDade, “Relative contributions of fossil and contemporary carbon sources to PM2.5 aerosols at nine Interagency Monitoring for Protection of Visual Environments (IMPROVE) network sites,” Journal of Geophysical Research, vol. 112, no. 10, Article ID D10205, 2007.
[59]
L. Ke, X. Ding, R. L. Tanner, J. J. Schauer, and M. Zheng, “Source contributions to carbonaceous aerosols in the Tennessee valley region,” Atmospheric Environment, vol. 41, no. 39, pp. 8898–8923, 2007.
[60]
Y. Cheng, M. Zheng, K.-B. He et al., “Comparison of two thermal-optical methods for the determination of organic carbon and elemental carbon: results from the southeastern United States,” Atmospheric Environment, vol. 45, no. 11, pp. 1913–1918, 2011.
[61]
G. C. Holzworth, “Mixing heights, wind speeds, and potential for urban air pollution throughout the contiguous United States,” Tech. Rep. AP-101, Environmental Protection Agency, Office of Air Programs Publication, 1972.
[62]
J. A. Gillies and A. W. Gertler, “Comparison and evaluation of chemically speciated mobile source PM2.5 particulate matter profiles,” Journal of the Air & Waste Management Association, vol. 50, no. 8, pp. 1459–1480, 2000.
[63]
J. D. Mcdonald, B. Zielinska, E. M. Fujita, J. C. Sagebiel, J. C. Chow, and J. G. Watson, “Fine particle and gaseous emission rates from residential wood combustion,” Environmental Science and Technology, vol. 34, no. 11, pp. 2080–2091, 2000.
[64]
T. Zeng and Y. Wang, “Nationwide summer peaks of OC/EC ratios in the contiguous United States,” Atmospheric Environment, vol. 45, no. 3, pp. 578–586, 2011.
[65]
B. J. Turpin and J. J. Huntzicker, “Secondary formation of organic aerosol in the Los Angeles basin: a descriptive analysis of organic and elemental carbon concentrations,” Atmospheric Environment, vol. 25A, no. 2, pp. 207–215, 1991.
