Journal of the Air Pollution Control Association
ISSN: 0002-2470 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/uawm16
A Lagrangian Model of the Los Angeles Smog Aerosol Warren H. White & Rudolf B. Husar To cite this article: Warren H. White & Rudolf B. Husar (1976) A Lagrangian Model of the Los Angeles Smog Aerosol, Journal of the Air Pollution Control Association, 26:1, 32-35, DOI: 10.1080/00022470.1976.10470216 To link to this article: http://dx.doi.org/10.1080/00022470.1976.10470216
Published online: 13 Mar 2012.
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Date: 09 June 2016, At: 05:05
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A Lagrangian Model of the Los Angeles Smog Aerosol
Warren H. White and Rudolf B. Husar W. M. Keck Laboratories of Environmental Health Engineering, California Institute of Technology
Smog aerosol can be related to sources, atmospheric transport, and particle growth through a Lagrangian model. Sample calculations indicate that the midday Pasadena aerosol is dominated by material produced in the atmosphere, and that the afternoon drop in aerosol mass is due to the advection of cleaner air. Numerical experiments suggest that control of primary particulate emissions without corresponding control of reactive gases would not substantially improve visibility.
of the primary aerosol.7*8 Based on this breakdown, they then synthesized the size spectrum of the Pasadena aerosol from the spectral contributions of the major sources.9-10 The use of chemical tracers allowed these investigators to bypass the consideration of atmospheric transport in estimating source contributions. For this very reason, they did not study the factors which determine the concentration and composition of aerosol at a given location and time. The purpose of this paper is to describe a simple model which relates the physical and chemical properties of the ambient aerosol to sources, atmospheric transport, and particle growth. Model Formulation
Smog aerosol is a heterogeneous mixture of particles from various sources. In recent years, a substantial amount has been learned about the physical and chemical nature of the Pasadena aerosol.1"6 It is now clear that much of the aerosol is not emitted directly, but is the product of reactions in the atmosphere.2-7 Friedlander and coworkers developed a chemical tracer method which allowed them to quantify the major sources 32
The incorporation of atmospheric transport into source receptor models is most simply accomplished from the Lagrangian point of view. Our analysis is based on a conceptual model of a vertical column which maintains its identity as it is transported with the air flow. The column extends from ground level up through the mixing layer, and material is gained or lost only through the base and not through the sides. The neglect of horizontal dispersion is appropriate for an environment dominated by area sources.11 Journal of the Air Pollution Control Association
Downloaded by [37.123.130.176] at 05:05 09 June 2016
The trajectory such an air column would follow can be calculated from the wind field.12 The trajectories arriving at Pasadena calculated from surface winds on Sept. 3,1969, are shown in Figure 1. These trajectories reflect the characteristic shift from a leisurely southerly flow of air in the morning to the usual westerly sea breeze in the afternoon.13'14 Mixing heights were estimated from the model of Edinger.15 The mixing heights for the beginning and end of a trajectory were taken from his averages, and a uniform lifting rate was assumed. The initial aerosol for each trajectory was set equal to a marine aerosol measured by the authors at El Segundo in Sept. 1972. The volume concentration of this aerosol was 16 AJm3/cm3 at 45% relative humidity, and the size distribution is shown in Figure 2. The relative importance of various sources and transformation mechanisms depends on the range of particle sizes under consideration. The large particle (Dp > 1.0 jun) fraction of the ambient aerosol is dominated by dusts, and the small particle (Dp < 0.1 nm) fraction is dominated by primary emissions from combustion sources.9 Because surface deposition and coagulation are effective removal mechanisms for the very large and very small particles, the quantity of material in each of these size ranges is strongly affected by transients from nearby primary sources. In contrast, most of the material in the intermediate (0.1 yum < Dp < 1.0 /Ltm) size range appears to be produced in the atmosphere.2 Material tends to accumulate in this relatively stable size range, which is thus more representative of large scale effects. Particles in the intermediate size range account for nearly all of the visibility reduction3 and are the ones inhaled most deeply into the lungs.16 Accordingly, sources and transformation mechanisms considered
0
5
10 mi.
0
8
16 km.
Auto organics/ Marine background
0.01
1.0
Figure 2. Normalized volume distributions of primary aerosols.
here are those most important for the (0.1 nm < Dp < 1.0 /urn) size range, although the entire submicron fraction must be treated in the analysis to allow for growth into this size range. The major sources of primary aerosol identified by Friedlander were soil dust, motor vehicle emissions and industrial emissions.8 The mass of soil dust is concentrated in particles larger than one micron,17 above the size range of interest to us. Although important in some areas of the Los Angeles Basin, industrial emissions are estimated to play a secondary role in the development of the Pasadena aerosol.7-10 Therefore, the only major primary source considered in the calculations was motor vehicle exhaust. The exhaust of automobiles using leaded gasoline contains roughly equal mass concentrations of organic and lead halide particles.18 Figure 2 shows the measured size distribution of emitted lead-containing particles19 and the calculated size distribution of the remaining exhaust aerosol,20 which is assumed to be organic material. Emission rates were calculated by combining data on the spatio-temporal distribution of traffic21 with a total particulate emission of 0.3 g/car mile.22 As noted earlier, much of the Pasadena smog aerosol is not primary, but is produced in the atmosphere from reactive gases. Existing smog chamber observations23'24 are consistent with the interpretation that a pseudo first order gas phase reaction is the rate-limiting step in this process. In such a system, the rate at which secondary aerosol is produced is determined by the rate at which condensable species are generated, and is independent of the existing aerosol. The distribution of condensable species onto the aerosol is governed by gas phase diffusion and by the affinity of individual particles for the condensable species. In our calculations, the rate of particulate production in the atmosphere was set proportional to the intensity of solar radiation and to the accumulated emissions of motor vehicle exhaust, with a one hour time lag:
= bl(t) p
(1)
Jo Figure 1. Calculated air trajectories arriving in Pasadena on 3 September 1969. Numbers give time of arrival, dots denote hour intervals.
January 1976
Volume 26, No. 1
Here R is the rate at which secondary aerosol mass is produced, / is the intensity of solar radiation, and E is the rate 33
Downloaded by [37.123.130.176] at 05:05 09 June 2016
at which exhaust is emitted. The constant b was chosen so that the calculated average concentration of converted material in the Pasadena aerosol during the period 0900-2000 on Sept. 3,1969 is 25 jttm3/cm3, in agreement with Friedlander's estimate.7 The significant feature of Eq. (1), as will be discussed in the next section, is the proportionality of R to the integral of E, rather than to E itself. This choice is suggested by the evidence from the experiments referenced above that a given charge of reacting gases is not "used up" quickly, but continues to produce particulate material over an extended time interval. Chamber experiments and field measurements in Pasadena indicate that the addition of material to the aerosol occurs by heterogeneous condensation on existing nuclei.2'23 Electron microscopic observations of ambient particles suggest that the chainlike aggregates of lead halide particles are not effective condensation nuclei and that most of the material is deposited on other types of nuclei such as automobile organics and sea salt. In our calculations, the converted material was assumed to condense on existing non lead halide particles according to the diffusional rate law25:
this approximately quadratic dependence on residence time that the calculated concentration of converted material increases so rapidly at midday. The evolution of the calculated aerosol size distribution along the midday trajectory is shown in Figure 4. Due to the nonlinear dependence of the conversion process on residence time, most of the aerosol growth occurs late in the trajectory, between 1000 and 1200. The calculated final size distribution is comparable with the size distribution actually measured, the calculated mass median particle diameter being slightly smaller than observed. The sensitivity of the model was tested with a large number of calculations in which assumptions and data were systematically varied. A sample of the results is shown in Table I, which shows how predicted light scattering coefficients depend on the growth law in Eq. (2) and on the rate of emission of organic particulates by motor vehicles, when all other factors are held constant. According to these figures, control of particulate emissions without corresponding control of gaseous emissions would not produce much improvement in visibility.
dDp = a ( C (2) dt Dp + 2X1 In expression (2), Dp is the particle diameter, X is the mean free path of the condensing vapor, C, and Co are the concentrations of this vapor far from the particle and at the surface, and / and a are constants.
Acknowledgments
This work was strongly influenced by Dr. S. K. Friedlander of the California Institute of Technology. It was supported by the California Air Resources Board Aerosol Characterization Study and by N.I.E.H.S. Training Grant # E S 00080-06. The contents do not necessarily reflect the views and policies of the sponsoring agencies.
Results
Results of calculations based on the above model are shown in Figures 3 and 4. These figures were produced by integrating the rate equations for aerosol growth along the hourly trajectories arriving at Pasadena, taking into account the spatio-temporal distribution of emissions. Both atmospheric transport and gas-to-particle conversion thereby influenced the characteristics of the calculated Pasadena aerosol. As Figure 3 shows, the diurnal variation of the calculated aerosol concentration is similar to that actually observed. Both calculated and observed aerosol volume increase rapidly during the late morning hours, reach a peak at midday, and drop sharply with the arrival of the marine layer in the afternoon. The variation of the calculated concentration of converted material indicates that the composition of the Pasadena aerosol undergoes marked changes during the day. Although primary material is an important constituent of the aerosol in the early morning and late afternoon, the midday aerosol is dominated by secondary species. It is instructive to compare the variation of aerosol concentration with the variation of residence time, also shown in Figure 3. If we assume that the air is clean at 0600 and that the mixing height and the emission rates are constant, then the concentration of primary material in an air parcel is proportional to the length of time, T, that the parcel has spent over land since 0600. If solar radiation were also constant, then according to Eq. (1) the rate of gas to particle conversion would be roughly proportional to T, so that the concentration of the converted matter accumulated in the parcel would be proportional to T 2 . It is primarily due to 34
90 Measured aerosol volume
Calculated aerosol volume
Calculated secondary aerosol volume
10 Residence time
10
11
12N 1 Time of day
Figure 3. Diurnal patterns in Pasadena aerosol on 3 September 1969. Top three curves show calculated and measured submicron aerosol volume concentrations; bottom curve shows estimated time spent over land since 6:00 by air mass.
Journal of the Air Pollution Control Association
300
1
' ' ' ' 1
- Calculated o Measured
250 -
f° \
•
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_
J\2:QV\
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o
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I
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Downloaded by [37.123.130.176] at 05:05 09 June 2016
ioo -
-
°J /l0:0cN
50 -
O
/ /
/
°°o 1 1 1
1.0
0.1
Figure 4. Volume distribution of midday Pasadena aerosol on 3 September 1969. Curves show development of calculated volume distribution along air trajectory arriving in Pasadena at 12:00; dots show volume distribution measured in Pasadena at 12:00.
References 1. P. K. Mueller, R. W. Mosley, and L. B. Pierce, "Chemical composition of Pasadena aerosol by particle size and time of day. IV. Carbonate and non-carbonate carbon content," J. Colloid Interface Sci. 39: 235 (1972). 2. R. B. Husar, K. T. Whitby, and B. Y. H. Liu, "Physical mechanisms governing the dynamics of Los Angeles smog aerosol," J. Colloid Interface Sci. 39: 211 (1972). 3. D. S. Ensor, R. J. Charlson, N. C. Ahlquist, K. T. Whitby, R. B. Husar, and B. Y. H. Liu, "Multiwavelength nephelometer measurements in Los Angeles smog aerosol I: Comparison of calculated and measured light scattering," J. Colloid Interface Sci. 39: 242 (1972). 4. K. T. Whitby, R. B. Husar, and B. Y. H. Liu, "The aerosol size distribution of Los Angeles smog," J. Colloid Interface Sci. 39: 177 (1972). 5. D. Grosjean and S. K. Friedlander, "Gas-particle distribution factors for organic and other pollutants in the Los Angeles atmosphere," J. Air Poll. Control Assoc. 25:1038 (1975). 6. G. M. Hidy, et al., "Characterization of Aerosols in California," Report SC524.25FR, Rockwell International Science Center, Thousand Oaks, CA, 19J4.
7. S. K. Friedlander, "Chemical element balances and the identification of air pollution sources," Environ. Sci. Technol. 7: 235 (1973). 8. M. S. Miller, S. K. Friedlander, and G. M. Hidy, "A chemical element balance for the Pasadena aerosol," J. Colloid Interface Sci. 39:165 (1972). 9. S. L. Heisler, S. K. Friedlander, and R. B. Husar, "The relationship of smog aerosol size and chemical element distributions to source characteristics," Atmos. Environ. 7: 633 (1973). 10. G. Gartrell, Jr. and S. K. Friedlander, "Relating particulate pollution to sources: the 1972 California aerosol characterization study," Atmos. Environ. 9: 279 (1975). 11. A. Q. Eschenroeder and J. R. Martinez, "Further Development of the Photochemical Smog Model for the Los Angeles Basin," Report CR-1-191, General Research Corporation, Santa Barbara, CA, 1971. 12. S. Petterssen, Weather Analysis and Forecasting, McGrawHill, New York, 1956. p. 27. 13. J. K. Angell, D. H. Pack, L. Machta, D. R. Dickson, and W. H. Hoecher, "Three-dimensional air trajectories determined from tetroon flights in the planetary boundary layer of the Los Angeles basin," J. Appl. Meteor. 11: 451 (1972). 14. M. Neiburger and J. G. Edinger, "Summary Report on Meteorology of the Los Angeles Basin With Particular Respect to the 'Smog' Problem," Southern California Air Pollution Foundation Report # 1, Los Angeles, CA, 1954. 15. J. G. Edinger, "Changes in the depth of the marine layer over the Los Angeles basin," J. Meteor. 16: 219 (1959). 16. K. A. Bell and S. K. Friedlander, "Aerosol deposition in models of a human lung bifurcation," Staub 33:178 (1973). 17. I. H. Blifford, Jr., "Tropospheric aerosols," J. Geophys. Res. 75: 3099 (1970). 18. J. M. Colucci and C. R. Begeman, "The automotive contribution to airborne polynuclear aromatic hydrocarbons in Detroit," J. Air Poll. Control Assoc. 15:113 (1965). 19. G. L. Ter Haar and R. E. Stephens, "The Effects of Automobile Exhaust Particulates on Visibility," paper presented at the "Twelfth Conference on Methods in Air Pollution and Industrial Hygiene Studies," Los Angeles, CA, April 1971. 20. K. T. Whitby, R. B. Husar, A. R. McFarland, and M. Tomaides, "Generation and Decay of Small Ions," Particle Laboratory Publication #137, Dept. of Mechanical Engineering, University of Minnesota, 1969. 21. P. J. W. Roberts, P. M. Roth, and C. L. Nelson, 'Contaminant Emissions in the Los Angeles Basin'—Appendix A of "Development of a Simulation Model for Estimating Ground Level Concentrations of Photochemical Pollutants," Report 71SAI6, Systems Applications, Inc., Beverly Hills, CA, 1971. 22. K. Habibi, "Characterization of the particulate matter in vehicle exhaust," Environ. Sci. Technol. 7: 223 (1973). 23. R. B. Husar and K. T. Whitby, "The growth rate and size spectrum of photochemical aerosols," Environ. Sci. Technol. 7: 241 (1973). 24. A. Goetz and R. F. Pueschel, "The effect of nucleating particulates on photochemical aerosol formation," J. Air Poll. Control Assoc. 15: 91 (1965). 25. N. A. Fuchs, "Recent Progress in the Theory of Transfer Processes in Aerosols at Intermediate Values of Knudsen Number," Proceedings of the 7th International Conference on Condensation and Ice Nuclei, Sept. 18-24, 1969, Prague and Vien-
Table I. Dependence of calculated light scattering coefficient on rate of organic particulate emissions from motor vehicles and form of particle growth law. 4
Calculated b s c a ^ (10" m "')
Emission rate (grams/mile) 0.05
Growth law
A Dp/At oc (Dp + 2ZA)"M 3.2 A Dp/At oc 1 3.3 A DplAt ccDp 2.6
January 1976
Volume 26, No. 1
0.10 3.4 3.6 3.1
0.15 3.6 3.8 3.5
0.20 3.7 4.0 3.8
Dr. White's present address is Meteorology Research, Inc., 464 W. Woodbury Road, Altadena, CA 91001. Dr. Husar's address is now Department of Mechanical Engineering, Washington University, St. Louis, MO 63130. This is a revision of Paper No. 73-111 which was presented at the 66th Annual Meeting of APCA at Chicago in June 1973.
35
ISSN: 0002-2470 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/uawm16
A Lagrangian Model of the Los Angeles Smog Aerosol Warren H. White & Rudolf B. Husar To cite this article: Warren H. White & Rudolf B. Husar (1976) A Lagrangian Model of the Los Angeles Smog Aerosol, Journal of the Air Pollution Control Association, 26:1, 32-35, DOI: 10.1080/00022470.1976.10470216 To link to this article: http://dx.doi.org/10.1080/00022470.1976.10470216
Published online: 13 Mar 2012.
Submit your article to this journal
Article views: 23
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=uawm16 Download by: [37.123.130.176]
Date: 09 June 2016, At: 05:05
Downloaded by [37.123.130.176] at 05:05 09 June 2016
A Lagrangian Model of the Los Angeles Smog Aerosol
Warren H. White and Rudolf B. Husar W. M. Keck Laboratories of Environmental Health Engineering, California Institute of Technology
Smog aerosol can be related to sources, atmospheric transport, and particle growth through a Lagrangian model. Sample calculations indicate that the midday Pasadena aerosol is dominated by material produced in the atmosphere, and that the afternoon drop in aerosol mass is due to the advection of cleaner air. Numerical experiments suggest that control of primary particulate emissions without corresponding control of reactive gases would not substantially improve visibility.
of the primary aerosol.7*8 Based on this breakdown, they then synthesized the size spectrum of the Pasadena aerosol from the spectral contributions of the major sources.9-10 The use of chemical tracers allowed these investigators to bypass the consideration of atmospheric transport in estimating source contributions. For this very reason, they did not study the factors which determine the concentration and composition of aerosol at a given location and time. The purpose of this paper is to describe a simple model which relates the physical and chemical properties of the ambient aerosol to sources, atmospheric transport, and particle growth. Model Formulation
Smog aerosol is a heterogeneous mixture of particles from various sources. In recent years, a substantial amount has been learned about the physical and chemical nature of the Pasadena aerosol.1"6 It is now clear that much of the aerosol is not emitted directly, but is the product of reactions in the atmosphere.2-7 Friedlander and coworkers developed a chemical tracer method which allowed them to quantify the major sources 32
The incorporation of atmospheric transport into source receptor models is most simply accomplished from the Lagrangian point of view. Our analysis is based on a conceptual model of a vertical column which maintains its identity as it is transported with the air flow. The column extends from ground level up through the mixing layer, and material is gained or lost only through the base and not through the sides. The neglect of horizontal dispersion is appropriate for an environment dominated by area sources.11 Journal of the Air Pollution Control Association
Downloaded by [37.123.130.176] at 05:05 09 June 2016
The trajectory such an air column would follow can be calculated from the wind field.12 The trajectories arriving at Pasadena calculated from surface winds on Sept. 3,1969, are shown in Figure 1. These trajectories reflect the characteristic shift from a leisurely southerly flow of air in the morning to the usual westerly sea breeze in the afternoon.13'14 Mixing heights were estimated from the model of Edinger.15 The mixing heights for the beginning and end of a trajectory were taken from his averages, and a uniform lifting rate was assumed. The initial aerosol for each trajectory was set equal to a marine aerosol measured by the authors at El Segundo in Sept. 1972. The volume concentration of this aerosol was 16 AJm3/cm3 at 45% relative humidity, and the size distribution is shown in Figure 2. The relative importance of various sources and transformation mechanisms depends on the range of particle sizes under consideration. The large particle (Dp > 1.0 jun) fraction of the ambient aerosol is dominated by dusts, and the small particle (Dp < 0.1 nm) fraction is dominated by primary emissions from combustion sources.9 Because surface deposition and coagulation are effective removal mechanisms for the very large and very small particles, the quantity of material in each of these size ranges is strongly affected by transients from nearby primary sources. In contrast, most of the material in the intermediate (0.1 yum < Dp < 1.0 /Ltm) size range appears to be produced in the atmosphere.2 Material tends to accumulate in this relatively stable size range, which is thus more representative of large scale effects. Particles in the intermediate size range account for nearly all of the visibility reduction3 and are the ones inhaled most deeply into the lungs.16 Accordingly, sources and transformation mechanisms considered
0
5
10 mi.
0
8
16 km.
Auto organics/ Marine background
0.01
1.0
Figure 2. Normalized volume distributions of primary aerosols.
here are those most important for the (0.1 nm < Dp < 1.0 /urn) size range, although the entire submicron fraction must be treated in the analysis to allow for growth into this size range. The major sources of primary aerosol identified by Friedlander were soil dust, motor vehicle emissions and industrial emissions.8 The mass of soil dust is concentrated in particles larger than one micron,17 above the size range of interest to us. Although important in some areas of the Los Angeles Basin, industrial emissions are estimated to play a secondary role in the development of the Pasadena aerosol.7-10 Therefore, the only major primary source considered in the calculations was motor vehicle exhaust. The exhaust of automobiles using leaded gasoline contains roughly equal mass concentrations of organic and lead halide particles.18 Figure 2 shows the measured size distribution of emitted lead-containing particles19 and the calculated size distribution of the remaining exhaust aerosol,20 which is assumed to be organic material. Emission rates were calculated by combining data on the spatio-temporal distribution of traffic21 with a total particulate emission of 0.3 g/car mile.22 As noted earlier, much of the Pasadena smog aerosol is not primary, but is produced in the atmosphere from reactive gases. Existing smog chamber observations23'24 are consistent with the interpretation that a pseudo first order gas phase reaction is the rate-limiting step in this process. In such a system, the rate at which secondary aerosol is produced is determined by the rate at which condensable species are generated, and is independent of the existing aerosol. The distribution of condensable species onto the aerosol is governed by gas phase diffusion and by the affinity of individual particles for the condensable species. In our calculations, the rate of particulate production in the atmosphere was set proportional to the intensity of solar radiation and to the accumulated emissions of motor vehicle exhaust, with a one hour time lag:
= bl(t) p
(1)
Jo Figure 1. Calculated air trajectories arriving in Pasadena on 3 September 1969. Numbers give time of arrival, dots denote hour intervals.
January 1976
Volume 26, No. 1
Here R is the rate at which secondary aerosol mass is produced, / is the intensity of solar radiation, and E is the rate 33
Downloaded by [37.123.130.176] at 05:05 09 June 2016
at which exhaust is emitted. The constant b was chosen so that the calculated average concentration of converted material in the Pasadena aerosol during the period 0900-2000 on Sept. 3,1969 is 25 jttm3/cm3, in agreement with Friedlander's estimate.7 The significant feature of Eq. (1), as will be discussed in the next section, is the proportionality of R to the integral of E, rather than to E itself. This choice is suggested by the evidence from the experiments referenced above that a given charge of reacting gases is not "used up" quickly, but continues to produce particulate material over an extended time interval. Chamber experiments and field measurements in Pasadena indicate that the addition of material to the aerosol occurs by heterogeneous condensation on existing nuclei.2'23 Electron microscopic observations of ambient particles suggest that the chainlike aggregates of lead halide particles are not effective condensation nuclei and that most of the material is deposited on other types of nuclei such as automobile organics and sea salt. In our calculations, the converted material was assumed to condense on existing non lead halide particles according to the diffusional rate law25:
this approximately quadratic dependence on residence time that the calculated concentration of converted material increases so rapidly at midday. The evolution of the calculated aerosol size distribution along the midday trajectory is shown in Figure 4. Due to the nonlinear dependence of the conversion process on residence time, most of the aerosol growth occurs late in the trajectory, between 1000 and 1200. The calculated final size distribution is comparable with the size distribution actually measured, the calculated mass median particle diameter being slightly smaller than observed. The sensitivity of the model was tested with a large number of calculations in which assumptions and data were systematically varied. A sample of the results is shown in Table I, which shows how predicted light scattering coefficients depend on the growth law in Eq. (2) and on the rate of emission of organic particulates by motor vehicles, when all other factors are held constant. According to these figures, control of particulate emissions without corresponding control of gaseous emissions would not produce much improvement in visibility.
dDp = a ( C (2) dt Dp + 2X1 In expression (2), Dp is the particle diameter, X is the mean free path of the condensing vapor, C, and Co are the concentrations of this vapor far from the particle and at the surface, and / and a are constants.
Acknowledgments
This work was strongly influenced by Dr. S. K. Friedlander of the California Institute of Technology. It was supported by the California Air Resources Board Aerosol Characterization Study and by N.I.E.H.S. Training Grant # E S 00080-06. The contents do not necessarily reflect the views and policies of the sponsoring agencies.
Results
Results of calculations based on the above model are shown in Figures 3 and 4. These figures were produced by integrating the rate equations for aerosol growth along the hourly trajectories arriving at Pasadena, taking into account the spatio-temporal distribution of emissions. Both atmospheric transport and gas-to-particle conversion thereby influenced the characteristics of the calculated Pasadena aerosol. As Figure 3 shows, the diurnal variation of the calculated aerosol concentration is similar to that actually observed. Both calculated and observed aerosol volume increase rapidly during the late morning hours, reach a peak at midday, and drop sharply with the arrival of the marine layer in the afternoon. The variation of the calculated concentration of converted material indicates that the composition of the Pasadena aerosol undergoes marked changes during the day. Although primary material is an important constituent of the aerosol in the early morning and late afternoon, the midday aerosol is dominated by secondary species. It is instructive to compare the variation of aerosol concentration with the variation of residence time, also shown in Figure 3. If we assume that the air is clean at 0600 and that the mixing height and the emission rates are constant, then the concentration of primary material in an air parcel is proportional to the length of time, T, that the parcel has spent over land since 0600. If solar radiation were also constant, then according to Eq. (1) the rate of gas to particle conversion would be roughly proportional to T, so that the concentration of the converted matter accumulated in the parcel would be proportional to T 2 . It is primarily due to 34
90 Measured aerosol volume
Calculated aerosol volume
Calculated secondary aerosol volume
10 Residence time
10
11
12N 1 Time of day
Figure 3. Diurnal patterns in Pasadena aerosol on 3 September 1969. Top three curves show calculated and measured submicron aerosol volume concentrations; bottom curve shows estimated time spent over land since 6:00 by air mass.
Journal of the Air Pollution Control Association
300
1
' ' ' ' 1
- Calculated o Measured
250 -
f° \
•
3
_
J\2:QV\
200 _
o
1
I
150 -
A
/ir.oo\
\ ° -
Downloaded by [37.123.130.176] at 05:05 09 June 2016
ioo -
-
°J /l0:0cN
50 -
O
/ /
/
°°o 1 1 1
1.0
0.1
Figure 4. Volume distribution of midday Pasadena aerosol on 3 September 1969. Curves show development of calculated volume distribution along air trajectory arriving in Pasadena at 12:00; dots show volume distribution measured in Pasadena at 12:00.
References 1. P. K. Mueller, R. W. Mosley, and L. B. Pierce, "Chemical composition of Pasadena aerosol by particle size and time of day. IV. Carbonate and non-carbonate carbon content," J. Colloid Interface Sci. 39: 235 (1972). 2. R. B. Husar, K. T. Whitby, and B. Y. H. Liu, "Physical mechanisms governing the dynamics of Los Angeles smog aerosol," J. Colloid Interface Sci. 39: 211 (1972). 3. D. S. Ensor, R. J. Charlson, N. C. Ahlquist, K. T. Whitby, R. B. Husar, and B. Y. H. Liu, "Multiwavelength nephelometer measurements in Los Angeles smog aerosol I: Comparison of calculated and measured light scattering," J. Colloid Interface Sci. 39: 242 (1972). 4. K. T. Whitby, R. B. Husar, and B. Y. H. Liu, "The aerosol size distribution of Los Angeles smog," J. Colloid Interface Sci. 39: 177 (1972). 5. D. Grosjean and S. K. Friedlander, "Gas-particle distribution factors for organic and other pollutants in the Los Angeles atmosphere," J. Air Poll. Control Assoc. 25:1038 (1975). 6. G. M. Hidy, et al., "Characterization of Aerosols in California," Report SC524.25FR, Rockwell International Science Center, Thousand Oaks, CA, 19J4.
7. S. K. Friedlander, "Chemical element balances and the identification of air pollution sources," Environ. Sci. Technol. 7: 235 (1973). 8. M. S. Miller, S. K. Friedlander, and G. M. Hidy, "A chemical element balance for the Pasadena aerosol," J. Colloid Interface Sci. 39:165 (1972). 9. S. L. Heisler, S. K. Friedlander, and R. B. Husar, "The relationship of smog aerosol size and chemical element distributions to source characteristics," Atmos. Environ. 7: 633 (1973). 10. G. Gartrell, Jr. and S. K. Friedlander, "Relating particulate pollution to sources: the 1972 California aerosol characterization study," Atmos. Environ. 9: 279 (1975). 11. A. Q. Eschenroeder and J. R. Martinez, "Further Development of the Photochemical Smog Model for the Los Angeles Basin," Report CR-1-191, General Research Corporation, Santa Barbara, CA, 1971. 12. S. Petterssen, Weather Analysis and Forecasting, McGrawHill, New York, 1956. p. 27. 13. J. K. Angell, D. H. Pack, L. Machta, D. R. Dickson, and W. H. Hoecher, "Three-dimensional air trajectories determined from tetroon flights in the planetary boundary layer of the Los Angeles basin," J. Appl. Meteor. 11: 451 (1972). 14. M. Neiburger and J. G. Edinger, "Summary Report on Meteorology of the Los Angeles Basin With Particular Respect to the 'Smog' Problem," Southern California Air Pollution Foundation Report # 1, Los Angeles, CA, 1954. 15. J. G. Edinger, "Changes in the depth of the marine layer over the Los Angeles basin," J. Meteor. 16: 219 (1959). 16. K. A. Bell and S. K. Friedlander, "Aerosol deposition in models of a human lung bifurcation," Staub 33:178 (1973). 17. I. H. Blifford, Jr., "Tropospheric aerosols," J. Geophys. Res. 75: 3099 (1970). 18. J. M. Colucci and C. R. Begeman, "The automotive contribution to airborne polynuclear aromatic hydrocarbons in Detroit," J. Air Poll. Control Assoc. 15:113 (1965). 19. G. L. Ter Haar and R. E. Stephens, "The Effects of Automobile Exhaust Particulates on Visibility," paper presented at the "Twelfth Conference on Methods in Air Pollution and Industrial Hygiene Studies," Los Angeles, CA, April 1971. 20. K. T. Whitby, R. B. Husar, A. R. McFarland, and M. Tomaides, "Generation and Decay of Small Ions," Particle Laboratory Publication #137, Dept. of Mechanical Engineering, University of Minnesota, 1969. 21. P. J. W. Roberts, P. M. Roth, and C. L. Nelson, 'Contaminant Emissions in the Los Angeles Basin'—Appendix A of "Development of a Simulation Model for Estimating Ground Level Concentrations of Photochemical Pollutants," Report 71SAI6, Systems Applications, Inc., Beverly Hills, CA, 1971. 22. K. Habibi, "Characterization of the particulate matter in vehicle exhaust," Environ. Sci. Technol. 7: 223 (1973). 23. R. B. Husar and K. T. Whitby, "The growth rate and size spectrum of photochemical aerosols," Environ. Sci. Technol. 7: 241 (1973). 24. A. Goetz and R. F. Pueschel, "The effect of nucleating particulates on photochemical aerosol formation," J. Air Poll. Control Assoc. 15: 91 (1965). 25. N. A. Fuchs, "Recent Progress in the Theory of Transfer Processes in Aerosols at Intermediate Values of Knudsen Number," Proceedings of the 7th International Conference on Condensation and Ice Nuclei, Sept. 18-24, 1969, Prague and Vien-
Table I. Dependence of calculated light scattering coefficient on rate of organic particulate emissions from motor vehicles and form of particle growth law. 4
Calculated b s c a ^ (10" m "')
Emission rate (grams/mile) 0.05
Growth law
A Dp/At oc (Dp + 2ZA)"M 3.2 A Dp/At oc 1 3.3 A DplAt ccDp 2.6
January 1976
Volume 26, No. 1
0.10 3.4 3.6 3.1
0.15 3.6 3.8 3.5
0.20 3.7 4.0 3.8
Dr. White's present address is Meteorology Research, Inc., 464 W. Woodbury Road, Altadena, CA 91001. Dr. Husar's address is now Department of Mechanical Engineering, Washington University, St. Louis, MO 63130. This is a revision of Paper No. 73-111 which was presented at the 66th Annual Meeting of APCA at Chicago in June 1973.
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