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TECHNICAL REPORT
Atmospheric Pollutants and Trace Gases

Aerosol Chemical and Optical Properties during the Mt. Zirkel Visibility Study

^a Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512
^b University of Alaska, 303 IARC, Fairbanks, AK 99775
^c Sonoma Technology, Inc., 1360 Redwood Way, Suite C, Petaluma, CA 94954
^d Univ. of La Laguna, Tenerife, Canary Islands, Spain

* Corresponding author (johnw{at}dri.edu)

Received for publication March 31, 2000.

	ABSTRACT

TOP ABSTRACT INTRODUCTION METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Aerosol chemical and optical properties were measured near the Mt. Zirkel Wilderness Area in northwestern Colorado. Six-hour PM_2.5 (particles with aerodynamic diameters less than 2.5 µm) mass concentrations and PM_2.5 dry particle light scattering at 550 nm averaged 4.6 µg m^-3 and 8.6 Mm^-1, respectively. Sulfates, organic carbon, and geological material were the principle components of particle mass and light scattering. Hygroscopic growth was consistent with that expected for ammonium sulfate aerosols. Size distributions derived from three-wavelength (i.e., 450, 550, and 700 nm) nephelometer data were similar to those measured in other remote areas of the western USA. Quasi-dry chemical light scattering efficiencies derived using Mie theory were 3.6 m² g^-1 for organic carbon, 2.5 m² g^-1 for sulfates (ammonium sulfate and ammonium bisulfate), 2.6 m² g^-1 for ammonium nitrate, and 1.76 m² g^-1 for geological material. These values are lower than but consistent with previously reported results. Realistic efficiencies could not be derived using the multiple linear regression (MLR) approach.

Abbreviations: AAE, average absolute error • EC, elemental carbon • ELSIE, Elastic Light Scattering Interactive Efficiencies model • GCVTC, Grand Canyon Visibility Transport Commission • GMD, geometric mean diameter • GSTD, geometric standard deviation • MLR, multiple linear regression • Mm^-1, inverse megameter (1/10⁶ m) • MZVS, Mt. Zirkel Visibility Study • OC, organic carbon • PM_2.5, particles with aerodynamic diameters less than 2.5 µm • RH, relative humidity

	INTRODUCTION

TOP ABSTRACT INTRODUCTION METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
THE major cause of excessive haze in urban and nonurban areas is light scattering and absorption by suspended particles (Sloane and White, 1986; Malm et al., 1994; Watson and Chow, 1994). To require additional pollution controls on an existing industrial source or a group of sources outside 156 U.S. National Parks and Wilderness Areas, USEPA regulations require a perceptible increment in visibility impairment to be "reasonably attributable" to those sources (USEPA, 1980, 1999a,b). The Mt. Zirkel Wilderness Area (MZWA) in the Routt National Forest of northwestern Colorado (Fig. 1) is subject to these regulations. Potential contributors to haze-causing particles in the MZWA include the Craig and Hayden coal-fired power stations and the Steamboat Springs, Hayden, and Craig population centers located in the Yampa Valley west of the Wilderness. Other contributors include more distant emitters in northwestern Colorado, southern Wyoming, and western Utah. The Mt. Zirkel Visibility Study (MZVS) (Watson et al., 1996) was conducted in 1995 to determine: (i) the extent of visibility impairment, if any, within the MZWA; (ii) whether the cause of or contribution to any visibility impairment within the MZWA may be reasonably attributed to emissions from any source or group of sources; and (iii) the relative contribution of emissions from each source or group of sources to visibility impairment.

View larger version (54K): [in this window] [in a new window]   Fig. 1. Mt. Zirkel Visibility Study area.

	METHODS

TOP ABSTRACT INTRODUCTION METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Figure 1 shows the MZVS study domain, which included multiple sites within and outside of the Yampa Valley. The Buffalo Pass site (elevation 3224 m above mean sea level) was intended to represent visibility and aerosol concentrations in the wilderness, especially at high elevations and at its southern extreme, which is closest to Yampa Valley emissions sources. Ambient measurements were acquired from 1 Dec. 1994 through 30 Nov. 1995. Daytime 6-h average (0600–1200 and 1200–1800 mountain standard time [MST]) aerosol and light scattering measurements from summer (3 Aug. 1995–2 Sept. 1995) and fall (15 Sept. 1995–15 Oct. 1995) are included in these analyses because visibility was poorer than during winter and spring.

Hourly particle light scattering (bsp) measurements were acquired with two different types of nephelometers. A TSI (Minneapolis, MN) 3563 nephelometer (Bodhaine et al., 1991; Anderson et al., 1996; Anderson and Ogren, 1998) preceded by a PM_2.5 size-selective inlet measured bsp at three wavelengths: 450 nm (blue, bspb), 550 nm (green, bspg), and 700 nm (red, bspr). This instrument was located in a heated shelter, exposing the sampled particles to an average relative humidity (RH) of 31 ± 11%, thereby approximating dry particle scattering. Because the particles were heated, some of the volatile components (e.g., ammonium nitrate, organic carbon) may have been lost, resulting in an underestimation of bsp by the TSI nephelometer. An open-air Optec (Fort Collins, CO) NGN-2 nephelometer (Molenar, 1997) measured total particle scattering at a wavelength of 550 nm at near-ambient humidity with no size-selective inlet. Hourly ambient relative humidity was also recorded.

Morning and afternoon PM_2.5 samples were collected with medium-volume sequential filter samplers (SFS) (Chow et al., 1996). The sample was preceded by a PM_2.5 size-selective inlet followed by sodium carbonate–coated, anodized aluminum tubes to remove gaseous nitric acid from the sample stream. Aluminum denuders of this type have been shown to remove >95% of the nitric acid in the air stream, even in highly polluted environments (Fitz and Hering, 1996; John et al., 1988). Two filter packs sampled concurrently at flow rates of 55 L min^-1 each. One filter pack contained a Teflon-membrane filter (Gelman [Ann Arbor, MI] #R2PJ047) for gravimetric and elemental analysis followed downstream by a quartz-fiber filter (Pallflex #2500 QAT-UP; Pall Gelman Laboratory, Ann Arbor, MI) to collect volatile organics (Turpin et al., 1994). A parallel filter pack contained a quartz-fiber filter for analysis of inorganic ions, organic carbon (OC), and elemental carbon (EC), followed downstream by a sodium chloride (NaCl)–impregnated cellulose-fiber filter for analysis of nitrate volatilized from the front quartz-fiber filter during sampling and any ambient gaseous nitric acid not trapped by the denuder.

The Teflon membrane filters were analyzed for mass by gravimetry on a Cahn 31 electronic balance (Thermo Cahn, Madison, WI) after equilibration at RH < 20% and for elements by X-ray fluorescence (XRF) (Watson et al., 1999) on a Kevex Model 700/8000 energy dispersive x-ray fluorescence analyzer (Kevex X-Ray, Scotts Valley, CA). The front quartz-fiber filter was analyzed for water-soluble chloride, nitrate, and sulfate with a Dionex (Sunnyvale, CA) 2020i ion chromatograph on an AS-4 column (Chow and Watson, 1999); for water-soluble potassium by flame atomic absorption spectrophotometry (Chow et al., 2002) on a Varian (Palo Alto, CA) SpectrAA-880; and for water-soluble ammonium by automated colorimetry on a Technicon (Tarrytown, NY) TRAACS autoanalyzer using the indophenol method. The backup NaCl-impregnated filter was analyzed for nitrate by ion chromatography. The front and backup quartz-fiber filters were analyzed for undifferentiated OC and EC using the IMPROVE thermal–optical reflectance method (Chow et al., 1993, 2001). Although chemical-specific size distributions measured with MOUDI impactors (e.g., Sloane et al., 1991) were considered in the MZVS study design, the low concentrations, limited access, and unpredictable visibility events made these measurements impractical. Particle light extinction was estimated with Mie theory using the ELSIE (Elastic Light Scattering Interactive Efficiencies) model (Sloane, 1986; Lowenthal et al., 1995).

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Aerosol Composition
Average morning (0600 to 1200 MST) and afternoon (1200 to 1800 MST) PM_2.5 mass and chemical concentrations at the Buffalo Pass site are summarized in Table 1. During the summer and fall of 1995, average 6-h daytime mass was 4.6 ± 2.2 µg m^-3 with a range of 0.95 to 9.0 µg m^-3, excluding one apparent outlier (20 µg m^-3, on 24 Aug. 1995, 0600 to 1200 MST). The PM_2.5 nonvolatilized, volatilized, and total particulate nitrate and ammonium are presented, but volatilized ammonium and nitrate were a small fraction (1%) of PM_2.5 measured on the Teflon filter. While nitrate was a minor PM_2.5 component, more than one-third of the total particulate nitrate had volatilized during sampling. In addition to carbonaceous and inorganic secondary aerosol, a geological material component was calculated by converting the major crustal species to their oxides (Zhang et al., 1994). The relative abundances of nonvolatilized ammonium, nitrate, and sulfate indicate that sulfate was fully neutralized as ammonium sulfate in most cases. The average molar ratio of ammonium to sulfate was 1.9.

Measured and reconstructed mass (sum of sulfate, nonvolatized nitrate and ammonium, 1.4 x OC [to account for unmeasured hydrogen and oxygen], EC, and geological material) are compared in Fig. 2. The OC component is the front-filter OC, front-filter minus backup-filter OC (assuming positive organic artifact), and front-filter plus backup-filter OC (assuming negative organic artifact) in Fig. 2a,b,c, respectively. The average ratios of reconstructed to measured mass based on front-filter OC (no correction), OC corrected for positive artifact, and OC corrected for negative artifact are 0.88, 0.59, and 1.26, respectively.

View larger version (24K): [in this window] [in a new window]   Fig. 2. Measured PM2.5 (particles with aerodynamic diameters less than 2.5 µm) mass versus reconstructed mass with (a) front-filter organic carbon, (b) front-filter minus backup-filter organic carbon, (c) front-filter plus backup-filter organic carbon.

Particle Light Scattering
The average particle light scattering measured by the TSI instrument at 550 nm (8.53 Mm^-1) was comparable with Rayleigh scattering by atmospheric gases (8.42 Mm^-1 at 3224 m). Linear regression of bspg vs. PM_2.5 mass with effective-variance weighting (Watson et al., 1984) and intercept forced to zero yields a slope of 1.91 ± 0.12 m² g^-1 (r² = 0.85) as the dry mass scattering efficiency at 550 nm. The average ratio of dry particle light scattering to PM_2.5 (2.3 ± 1.0 m² g^-1) was comparable in magnitude with the linear regression slope.

Figure 3 shows how the ratio of hourly ambient total particle scattering (Optec bsp) to "quasi"-dry PM_2.5 particle scattering (TSI bspg) changes with increasing RH. Periods influenced by cloud were excluded from Fig. 3. Also plotted in Fig. 3 is the hygroscopic growth curve for ammonium sulfate reported by Tang and Munkelwitz (1994). While the curve and data points are offset, growth inferred from the ratio of ambient to dry particle scattering is consistent with that expected for pure ammonium sulfate. Based on differences in spectral response and integration angle, Molenar (1997) estimated the Optec response to be about 3% greater than that of the TSI for 1-µm-diameter particles. For RH < 50% (i.e., dry conditions), the average ratio of total (Optec) to PM_2.5 (TSI) particle scattering was 0.87 ± 0.27. On average, coarse particle scattering was not detected within the uncertainties of the light scattering measurements.

View larger version (32K): [in this window] [in a new window]   Fig. 3. Hourly average ratio of Optec (ambient) total particle scattering to TSI (quasi-dry) PM2.5 (particles with aerodynamic diameters less than 2.5 µm) particle scattering (bsp) at 550 nm as a function of relative humidity (RH) (N = 1125).

[1]

where Qsp(m,,D) is the optical scattering efficiency at wavelength , m is the particle refractive index, D is the particle diameter, and n(D) is the number size distribution function (Seinfeld and Pandis, 1998). For multiple wavelengths, Eq. [1] becomes a series of simultaneous equations that can in principle be solved or inverted to obtain the size distribution.

Size distributions were derived for 62 aerosol sample periods from the corresponding time-integrated TSI nephelometer measurements at 450, 550, and 700 nm using the method of King et al. (1978). The kernel function for the inversion contains the optical cross section (optical efficiency times geometric cross section) and the Jungian power function [(D/2)^-(+1)] (King et al., 1978; González Jorge and Ogren, 1996). The exponents are calculated from the empirical relation of Angstrom:

[2]

where is the wavelength and å = ( - 2). Since the shape of the size distribution is partially constrained in the inversion with the power law, it is possible to retrieve the size distribution in a larger number of discrete bins than the number of wavelengths. In this case, particle number and volume in 15 discrete bins were retrieved, as in González Jorge and Ogren (1996). The diameter interval was selected (Heintzenberg et al., 1981) based on the variations of the ratios of optical efficiencies at 450, 550, and 700 nm with respect to particle size. According to this criterion, there is independent information about the size distributions for diameters between 0.18 and 4 µm. Although the upper limit was further constrained by the size cutoff of the TSI nephelometer (2.5 µm), coarse particle concentrations were expected to be low, owing to vegetation and substantial precipitation at the measurement site.

It was assumed that all of the chemical components were internally mixed with a sample-specific refractive index, calculated as the volume-weighted average of the refractive indices of the components. The refractive index was assumed to be constant with particle size and wavelength. Sulfate was assumed to be fully neutralized as ammonium sulfate or partially neutralized as ammonium bisulfate, depending on the measured abundances of ammonium, nitrate, and sulfate. Water mass associated with sulfate and nitrate at the TSI RH was estimated using water activity data of Tang and Munkelwitz (1994) and Chan et al. (1992). Organic carbon was assumed to be nonhygroscopic (Malm et al., 1996). Assuming that the aerosol was completely dry would have changed the real and imaginary parts of the refractive index by less than 1 and 5%, respectively.

The resulting size distributions yield volume-weighted geometric mean diameters (GMD) averaging 0.29 ± 0.08 µm and ranging from 0.20 to 0.56 µm. Geometric standard deviations (GSTD) averaged 1.82 ± 0.36 and ranged from 1.23 to 2.6. For comparison, Pitchford and Green (1997) and Turpin et al. (1997) reported typical sulfur and sulfate GMD of about 0.3 µm at Meadview, AZ, during the summer of 1992 under low-humidity conditions. Although the inversion technique fits the measured scattering to within a few percent, the results are not unique. For example, Dellago and Horvath (1993) showed that two lognormal distributions with different GMDs, GSTDs, and particle volumes can produce the same spectral extinction. The uncertainties associated with this approach are discussed in detail by Heintzenberg et al. (1981) and González Jorge and Ogren (1996). This is a fundamental limitation of using a three-wavelength nephelometer to infer size distributions. The method does, however, substantially constrain the possible size distributions from all possibilities.

To validate these results, particle volumes were estimated from the measured chemical concentrations and their densities. The average absolute error (AAE), the average of the absolute differences between the measured and model-derived particle volume divided by the measured particle volume for each sample, expressed as a percent, was 35 ± 25%. The derived size distributions are self-consistent in one important respect—because geological material is overwhelmingly associated with particles larger than 2.5 µm (e.g., Chow et al., 1996), Buffalo Pass samples with large geological material fractions should have larger derived GMDs. This is indeed the case, as shown in Fig. 4, where the correlation between derived GMD and the ratio of geological material to the reconstructed mass is 0.62.

View larger version (13K): [in this window] [in a new window]   Fig. 4. Relationship between the derived geometric mean diameter (GMD) and the ratio of geological dust concentration to reconstructed mass.

Relationship between Chemical Composition and Light Scattering
Light scattering has been assigned to aerosol chemical components using scattering efficiencies derived from (i) multiple linear regression (MLR) (White and Roberts, 1977); (ii) Mie theory (Sloane, 1986; Zhang et al., 1994; Lowenthal et al., 1995); and (iii) "consensus" or literature values (e.g., Malm et al., 1996).

Results of MLR of bspg on sulfate (as ammonium sulfate), nitrate (as ammonium nitrate), organic carbon (as 1.4 x front-filter OC), and geological dust are presented in Table 2. To minimize the effects of hygroscopic growth, only samples (N = 52) with RH < 40% were considered. The resulting efficiencies differ from those of past studies. The sulfate and nitrate efficiencies are high (>5 m² g^-1) compared with those presented by Lowenthal et al. (2000) for Meadview, AZ. Indeed, scattering efficiencies of pure ammonium sulfate particles distributed log-normally with GMD of 0.2 and 0.4 µm and GSTD of 1.5 are 1.61 and 4.2 m² g^-1, respectively, at a wavelength of 550 nm. The OC efficiency of 1.07 m² g^-1 is also lower than expected and the geological dust efficiency is negative.

The results obtained here do not imply that MLR does not work. Data quality obviously plays a role in the MLR results. Aerosol concentrations and light scattering levels were very low at this remote site. By contrast, Lowenthal et al. (1995) reported reasonable MLR results for Meadview in the Grand Canyon and Phoenix, AZ. Malm et al. (2000) reported excellent results based on MLR for Great Smokey Mountains National Park, where average PM_2.5 concentrations were six times higher than those found at Buffalo Pass.

Scattering efficiencies for the chemical components (ammonium sulfate or ammonium bisulfate, ammonium nitrate, organic carbon, and geological dust) were estimated using the ELSIE model, as described by Lowenthal et al. (1995). Hygroscopic growth was estimated for the relative humidity in the TSI nephelometer, as described above. The average scattering efficiency and reconstructed scattering coefficient (the average of the product of the individual sample scattering efficiency and the corresponding chemical concentration) associated with each component are presented in Table 3. Backup-filter OC was neither subtracted nor added to the front-filter OC concentration. These values are compared with the corresponding scattering efficiencies adopted by the Grand Canyon Visibility Transport Commission (GCVTC) to evaluate visibility impairment in Class I areas along the Colorado Plateau (Ryan and Kendall, 1996). In this case, the effects of hygroscopic growth for RH 30% are accounted for using the growth function:

[3]

View larger version (17K): [in this window] [in a new window]   Fig. 5. Comparison of measured dry PM2.5 (particles with aerodynamic diameters less than 2.5 µm) particle scattering (bspg) based on uncorrected front-filter organic carbon (OC) with (a) particle scattering reconstructed from the Elastic Light Scattering Interactive Efficiencies (ELSIE) model and (b) particle scattering (bsp) based on Grand Canyon Visibility Transport Commission (GCVTC) scattering efficiencies (outlier excluded from regression).

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Six-hour average PM_2.5 mass concentrations and dry particle scattering during the MZVS at Buffalo Pass, CO were low, averaging 4.6 µg m^-3 and 8.6 Mm^-1, respectively. Sulfates, organic carbon uncorrected for potential sampling artifacts, and geological material were the major components of PM_2.5 mass. Hygroscopic growth inferred from the ratio of total (Optec nephelometer) to PM_2.5 (TSI nephelometer) particle light scattering as a function of relative humidity was consistent with that expected for ammonium sulfate. Particle size distributions inverted from three-wavelength nephelometer data had an average volume geometric mean diameter (GMD) of 0.29 ± 0.08 µm and an average geometric standard deviation (GSTD) of 1.82 ± 0.36. The derived size distributions reproduced the measured volume and particle light scattering to within 50 and 28%, respectively, in 43 out of 62 sample cases. In addition, the derived GMDs and the corresponding mass fractions of geological material, which are expected to be associated with relatively larger particles than sulfate, nitrate, or carbon, were reasonably correlated (r = 0.62). Average "quasi"-dry scattering efficiencies based on the derived size distributions were 3.6 m² g^-1 for organics (estimated as 1.4 x OC), 2.5 m² g^-1 for sulfates (ammonium sulfate and ammonium bisulfate), 2.6 m² g^-1 for ammonium nitrate, and 1.76 m² g^-1 for geological material. The multiple linear regression (MLR) approach was not able to resolve scattering efficiencies for individual chemical components. This might be caused by the low aerosol concentrations and scattering levels at this remote site and to correlations among the chemical species concentrations.

	REFERENCES

TOP ABSTRACT INTRODUCTION METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

• Anderson, T.L., D.S. Covert, S.F. Marshall, M.L. Laucks, R.J. Charlson, A.P. Waggoner, J.A. Ogren, R. Caldow, R.L. Holm, F.R. Quant, G.J. Sem, A. Wiedensohler, N.C. Ahlquist, and T.S. Bates. 1996. Performance characteristics of a high-sensitivity, three-wavelength, total scatter/backscatter nephelometer. J. Atmos. Oceanic Technol. 13:967–986.
• Anderson, T.L., and J.A. Ogren. 1998. Determining aerosol radiative properties using the TSI 3563 integrating nephelometer. Aerosol Sci. Technol. 29:57.
• Bodhaine, B.A., N.C. Ahlquist, and R.C. Schnell. 1991. Three-wavelength nephelometer suitable for aircraft measurement of background aerosol scattering coefficient. Atmos. Environ. 25A:2267–2276.
• Chan, C.K., R.C. Flagan, and J.H. Seinfeld. 1992. Water activities of NH₄NO₃/(NH₄)₂SO₄ solutions. Atmos. Environ. 26A:1661–1673.
• Chow, J.C., and J.G. Watson. 1999. Ion chromatography. p. 97–137. In S. Landsberger and M. Creatchman (ed.) Elemental analysis of airborne particles. Gordon and Breach, Newark, NJ.
• Chow, J.C., J.G. Watson, D. Crow, D.H. Lowenthal, and T. Merrifield. 2001. Comparison of IMPROVE and NIOSH carbon measurements. Aerosol Sci. Technol. 34:1–12.
• Chow, J.C., J.G. Watson, E.I. Hackett, R.H. Stone, and B.A. Hinsvark. 2002. Method no. 822: General atomic absorption procedure for trace metals in airborne material collected on filters. In J.P. Lodge (ed.) Methods of air sampling and analysis. 4th ed. Air and Waste Manage. Assoc., Pittsburgh, PA (in press).
• Chow, J.C., J.G. Watson, Z. Lu, D.H. Lowenthal, C.A. Frazier, P.A. Solomon, R.H. Thuillier, and K.L. Magliano. 1996. Descriptive analysis of PM_2.5 and PM₁₀ at regionally representative locations during SJVAQS/AUSPEX. Atmos. Environ. 30:2079–2112.
• Chow, J.C., J.G. Watson, L.C. Pritchett, W.R. Pierson, C.A. Frazier, and R.G. Purcell. 1993. The DRI thermal/optical reflectance carbon analysis system: Description, evaluation and applications in U.S. air quality studies. Atmos. Environ. 27A:1185–1201.
• Dellago, C., and H. Horvath. 1993. On the accuracy of the size distribution information obtained from light extinction and scattering measurements: I. Basic considerations and models. Atmos. Environ. 24:129–141.
• Eatough, D.J., F. Obeidi, Y. Pang, Y. Ding, N.L. Eatough, and W.E. Wilson. 1999. Integrated and real-time diffusion denuder sampler for PM_2.5. Atmos. Environ. 33:2835–2844.
• Eatough, D.J., H. Tang, W. Cui, and J. Machir. 1995. Determination of the size distribution and chemical composition of fine particulate semi-volatile organic material in urban environments using diffusion denuder technology. Inhalation Toxicol. 7:691–710.
• Eatough, D.J., A. Wadsworth, D.A. Eatough, J.W. Crawford, L.D. Hansen, and E.A. Lewis. 1993. A multiple-system, multi-channel diffusion denuder sampler for the determination of fine-particulate organic material in the atmosphere. Atmos. Environ. 27A:1213–1219.
• Fitz, D.R., and S.V. Hering. 1996. Study to evaluate the CADMP Sampler. Final report. No. 93-333. Prepared for California Air Resour. Board, Sacramento, CA. CE-CERT. Univ. of California, Riverside, CA.
• González Jorge, H., and J.A. Ogren. 1996. Sensitivity of retrieved aerosol properties to assumptions in the inversion of spectral optical depths. J. Atmos. Sci. 53:3669–3683.
• Heintzenberg, J. 1975. Determination in situ of the size distribution of the atmospheric aerosol. J. Aerosol Sci. 6:291–303.
• Heintzenberg, J. 1980. Particle size distribution and optical properties of Arctic haze. Tellus 32:251–260.
• Heintzenberg, J., H. Muller, H. Quenzel, and E. Thomalla. 1981. Information content of optical data with respect to aerosol properties: Numerical studies with a randomized minimum-search-technique inversion algorithm. Appl. Opt. 20:1308.
• John, W., S.M. Wall, and J.L. Ondo. 1988. A new method for nitric acid and nitrate aerosol measurement using the dichotomous sampler. Atmos. Environ. 22:1627–1636.
• King, M.D., D.M. Byrne, B.M. Herman, and J.A. Reagan. 1978. Aerosol size distributions obtained by inversion of spectral optical depth measurements. J. Atmos. Sci. 35:2153–2167.
• Lowenthal, D.H., C.F. Rogers, P. Saxena, J.G. Watson, and J.C. Chow. 1995. Sensitivity of estimated light extinction coefficients to model assumptions and measurement errors. Atmos. Environ. 29:751–766.
• Lowenthal, D.H., P. Saxena, and J.G. Watson. 2000. Contributions to light extinction during Project MOHAVE. Atmos. Environ. 34:2351–2359.
• Malm, W.C., D.E. Day, and S.M. Kreidenweis. 2000. Light scattering characteristics of aerosols as a function of relative humidity: Part I—A comparison of measured scattering and aerosol concentrations using the theoretical models. J. Air Waste Manage. Assoc. 50:686–700.
• Malm, W.C., J.V. Molenar, R.A. Eldred, and J.F. Sisler. 1996. Examining the relationship among atmospheric aerosols and light scattering and extinction in the Grand Canyon area. J. Geophys. Res. 101:19251–19266.
• Malm, W.C., J.F. Sisler, D. Huffman, R.A. Eldred, and T.A. Cahill. 1994. Spatial and seasonal trends in particle concentration and optical extinction in the United States. J. Geophys. Res. 99:1347–1370.
• Molenar, J.V. 1997. Analysis of the real world performance of the Optec NGN-2 ambient nephelometer. p. 243–265. In I.H. Tombach et al. (ed.) Proceedings, Visual Air Quality: Aerosols and Global Radiation Balance. Air and Waste Manage. Assoc., Pittsburgh, PA.
• Pitchford, M.L., and M.C. Green. 1997. Analyses of sulfur aerosol size distributions for a forty day period in summer, 1992 at Meadview, Arizona. J. Air Waste Manage. Assoc. 47:136–146.
• Ryan, P., and S. Kendall. 1996. Final reconciliation of transfer coefficients for use in the Integrated Assessment System. Ryan Consulting and Phelps Dodge Corp., Phoenix, AZ.
• Seinfeld, J.H., and S.N. Pandis. 1998. Atmospheric chemistry and physics: From air pollution to climate change. John Wiley & Sons, New York, NY.
• Sloane, C.S. 1986. Effect of composition on aerosol light scattering efficiencies. Atmos. Environ. 20:1025–1037.
• Sloane, C.S., J.G. Watson, J.C. Chow, L.C. Pritchett, and L.W. Richards. 1991. Size-segregated fine particle measurements by chemical species and their impact on visibility impairment in Denver. Atmos. Environ. 25A:1013–1024.
• Sloane, C.S., and W.H. White. 1986. Visibility: An evolving issue. Environ. Sci. Technol. 20:760–766.
• Tang, I.N., and H.R. Munkelwitz. 1994. Water activities, densities, and refractive indices of aqueous sulfates and sodium nitrate droplets of atmospheric importance. J. Geophys. Res. 99:18801–18808.
• Turpin, B.J., J.J. Huntzicker, and S.V. Hering. 1994. Investigation of organic aerosol sampling artifacts in the Los Angeles Basin. Atmos. Environ. 28:3061–3071.
• Turpin, B.J., P. Saxena, G.A. Allen, P. Koutrakis, P. McMurry, and L.M. Hildemann. 1997. Characterization of the southwestern desert aerosol, Meadview, AZ. J. Air Waste Manage. Assoc. 47:344–356.
• USEPA. 1980. 40 CFR Part 51—Requirements for preparation, adoption, and submittal of implementation plans. Fed. Regist. 45:80089.
• USEPA 1999a. 40 CFR Part 51—Regional haze regulations. Fed. Regist. 64:35714–35763.
• USEPA 1999b. 40 CFR Part 51—Requirements for preparation, adoption, and submittal of implementation plans. Fed. Regist. 64:35763–35774.
• Watson, J.G., D.L. Blumenthal, J.C. Chow, C.F. Cahill, L.W. Richards, D. Dietrich, R. Morris, J.E. Houck, R.J. Dickson, and S.R. Andersen. 1996. Mt. Zirkel Wilderness Area reasonable attribution study of visibility impairment—Volume II: Results of data analysis and modeling. Prepared for Colorado Dep. of Public Health and Environ., Denver, CO. Desert Res. Inst., Reno, NV.
• Watson, J.G., and J.C. Chow. 1994. Clear sky visibility as a challenge for society. Ann. Rev. Energy Environ. 19:241–266.
• Watson, J.G., J.C. Chow, and C.A. Frazier. 1999. X-ray fluorescence analysis of ambient air samples. p. 67–96. In S. Landsberger and M. Creatchman (ed.) Elemental analysis of airborne particles. Gordon and Breach, Newark, NJ.
• Watson, J.G., J.A. Cooper, and J.J. Huntzicker. 1984. The effective variance weighting for least squares calculations applied to the mass balance receptor model. Atmos. Environ. 18:1347–1355.[ISI]
• White, W.H. 1986. On the theoretical and empirical basis for apportioning extinction by aerosols: A critical review. Atmos. Environ. 20:1659–1672.
• White, W.H., and P.T. Roberts. 1977. On the nature and origins of visibility-reducing aerosols in the Los Angeles air basin. Atmos. Environ. 11:803–812.
• Zhang, X.Q., B.J. Turpin, P.H. McMurry, S.V. Hering, and M.R. Stolzenburg. 1994. Mie theory evaluation of species contributions to 1990 wintertime visibility reduction in the Grand Canyon. J. Air Waste Manage. Assoc. 44:153–162.

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