Rethinking the Ozone Problem in Urban and Regional Air Pollution (1991) / Chapter Skim
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8 Atmospheric Observations of VOCs, NOx, and Ozone
8 Atmospheric Observations of VOCs, NOx, and Ozone
Pages 211-250
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From page 211... ...
Two important points were made about the VOC/NOX ratio: First, the atmospheric boundary layer (defined here as a well-mixed layer extending from the surface to a height of about 1 or 2 km during the day) cannot be characterized by a single ratio because this ratio varies significantly with location and time of day.
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From page 212... ...
OBSERVATIONS OF OZONE Compared with those for NOX and VOCs, the data base of ozone observations is fairly extensive, especially for urban and suburban areas. At most rural surface sites, ozone concentrations have been found to vary over a diurnal cycle with a minimum in the early morning hours before dawn and a maximum in the late afternoon (Figure 8-1~.
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From page 213... ...
1 1 1 1 1 1 4 8 12 16 2.0 24 TIME OF DAY (fur) 213 FIGURE S-1 Diurnal behavior of ozone at rural sites in the United States in July.
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From page 214... ...
In remote locations, ozone concentrations tend to be quite low, typically ranging from 20 to 40 ppb. Table 8-1 Typical Summertime Daily Maximum Ozone Concentrations Region Ozone, ppb I Urban-suburban II Rural III Remote tropical forest IV Remote marine 100-400 50-120 20-4{)
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From page 215... ...
Four of the sites were downtown, where the average measured NOX concentration ranged from 40 to 99 ppb. At two suburban sites, the average concentrations were 33 ppb (upwind of the core city)
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From page 216... ...
: o ~ w~ off . lo on ding ~ of" ~ C'' ~ C''~- ~ ~ 9~ &''- ~ ~ ~q ~ FIGURE 8-2a NOX concentrations measured in urban locations in the United States during the summer of 1984.
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From page 217... ...
However, concentrations declined rapidly as the plume traveled away from the urban core. NOX concentrations in air masses 4-7 hours downwind of Boston were found to be 5-10 ppb.
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From page 218... ...
Although the data base is still quite sparse, concentrations in remote tropical forests (not under the direct influence of biomass burning) appear to range from 0.02 to 0.08 ppb; the somewhat higher NOX concentrations found in remote tropical forests, as compared with those observed in remote marine locations, could result from biogenic NOX emissions from soil (Kaplan et al.,1988; Torres and Buchan, 1988~.
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From page 219... ...
ATMOSPHERIC OBSERVATIONS TABLE 8-2 Locations 219 Average Concentrations Measured at Nonurban Monitoring NO, NO2, NOx, Reference Location ppb ppb ppb Research Fort McHenry, Maryland NDa 6b HD Triangle Dubois, Pennsylvania ND 1ob ND Institute, McConnelsville, Ohio ND 6b ND 1975 Wilmington, Ohio ND 6b ND Wooster, Ohio ND 6b ND Decker et Bradford, Pennsylvania 2 3b 5b al., 1976 Creston, Louisiana 4 2b 6b Deridder, Louisiana 1 3b 4b Martinez Montague, Massachusetts 2 3b 5b and Singh, Scranton, Pennsylvania 3 11b 14b 1979 Indian River, Delaware 3 5b 8b Research Triangle Park North Carolina 10 13b 23b Lewisburg, West Virginia 1 5b 6b Duncan Falls, Ohio 1 8b gb Fort Wayne, Indiana 3 7b 1ob Rockport, Indiana 3 7b 1ob Giles County, Tennessee 3 1ob 13b Jetmore, Kansas 1 4b 5b Pratt et al., Lamoure County, North 2.4 l7b 4lb 1983 Dakota 4.8 1,5b 6~3b 3.3 2.8b 6.1b 2.7 2,1b 4~8b Wright County, Minnesota 3.2 5,4b 8,6b 3,0 6,7b 9,7b 3.5 5,8b 9,3b 2.9 4,7b 7~6b Pratt et al., Traverse County, Minnesota 3.6 3,7b 7,3b 1983 4.8 3.6b 8~4b 4 0 2.9b 6~9b 2.0 2,2b 4~2b
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From page 220... ...
Kelly et al., 1980 Niwot Ridge, 0-2a Colorado Kelly et al., 1982 Pierre, South 1.2a Dakotab Kelly et al., 1984 Schaeffer <0.2 Observatory Whiteface Mountain, New York 1,1a Bollinger et al., 1984 Niwot Ridge, 0.80 Colorado Fehsenfeld et al., Niwot Ridge, 0.56 1987 Colorado Parrish et al., 1985 Point Arena, 0.37 California aUpper limit for NO2 and NOx bMeasurement site located 40 km WNW of Pierre.
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From page 221... ...
During the summer of 1986, NOy was measured at several rural sites In North America: Brasstown Bald Mountain, Georgia; Whitetop Mountain, North Carolina; Bondville, Illinois; Scotia, Pennsylvania; Egbert, Ontario; and Whiteface Mountain, New York. These were all rural sites in the industrial regions of the eastern United States or southern Canada.
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From page 222... ...
, a rural site in the eastern United States; Niwot Ridge, Colorado (Fahey et al., 1986; Parrish et al., 1988) , an isolated inland site in the western United States; Point Arena, California (Parrish et al., 1985)
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From page 223... ...
, three rural sites. Bars show range of measurements made.
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From page 224... ...
On the other hand, because anthropogenic VOC concentrations are usually largest during the early morning and biogenic emis
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From page 225... ...
The VOC data sets analyzed here are listed in Table 8-S. The analysis includes data gathered from 11 different areas: 5 urban-suburban areas in the United States, 2 rural sites in the eastern United States, 3 sites in the tropical forests of Brazil, and a region of the North Atlantic Ocean.
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From page 227... ...
227 ~ 3 ~ ~ ~ ~3 ~ ~S 2 ~e 11 ~o O _ , ~ ·~ ~ _ 0 ~ ~s v: s u' O O O O O O O O O O O O O O C~J ~O t- \8 ~ _ _ _ ~_ _ _ 1 1 1 1 1 1 1 O O O O O O O O O O O O O O ~oo ~d.
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From page 228... ...
228 a ° CQ d Cot 0= r .h Cat 0 o ._ _ C)
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From page 230... ...
230 ~ Zip U]
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From page 231... ...
over tropical forests suggest that it is not especially large. (When averaged over the atmospheric boundary layer, it is less than a factor of two.)
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From page 232... ...
To the extent that the measurements from a given site are representative of the average concentrations throughout the air mass, the OH-reactivity-based method provides a more rational basis for assessing the relative importance of the various VOCs in the air mass to ozone formation as well as for comparing the VOC concentrations in different air masses. The reader should note that the use of propylene's reactivity as
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From page 233... ...
The two highest ranking species using the concentration-based method are i-pentane and nbutane, two relatively unreactive compounds; the third highest ranking species is toluene, a moderately reactive compound. Isoprene, a highly reactive species normally associated with biogenic emissions, is ranked fifteenth using this method, with an average concentration of 4.6 ppbC; it constitutes only about Ho of the total VOCs present during the sampling period.
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From page 234... ...
234 RETHINKING THE OZONE PROBLEM based scale indicates that a significant fraction of the total organic carbon being cycled through the atmosphere at the Atlanta site originated from biogenic VOCs and thus that these species could be quite important. TABLE 8-6 Top 35 and Total VOCs Measured at Georgia Tech Campus, Atlanta, 1100-1400 Species sorted by concentration Species sorted by OH-reactivity Species Concentration, Species Propy ppbC Equiv., ppbC 1 i-pentane 19.8 1 isoprene 17.6 2 e-butane 16.9 2 p-cymene 10.4 3 toluene 14.7 3/m&p-xylene 7.1 4 p-cymene 11.0 4 2-methyl 5.9 2-butene 5 n-pentane 9.4 6 benzene 8.8 7 m&p-xylene 7.6 8 2-me-pentane 5.9 5 1,3,5-trime- 4.3 benzene 6 toluene 3.5 7 m&p-ethyl tolu- 3.4 ene 8 1,2,4-trime- 3.4 benzene 9 cyclohexane 5.4 9 t-2-pentane 3.1 10 2-me-hexane 5.2 10 iso-butene 3.1 11 ethane 5.0 11 i-pentane 3.1 12 undecane 4.9 12 t-2-butene 2.9 13 propane 4.8 13 c-2-butane 2.7 14 i-butane 4.8 14 undecane 2.3
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From page 235... ...
ATMOSPHERIC OBSERVATIONS 15 isoprene 4.6 15 1,4-diethyl 2.3 benzene 16 acetylene 4.3 16 c-2-pentene 2.2 17 n-hexane 3.8 17 cyclohexane 1.8 18 m&p-eth-tolu- 3.6 18 e-butane 1.7 ene 19 3-me-pentane 3.4 19 1,2,3-trime- 1.7 benzene 20 ethylene 3.0 20 o-xylene 1.6 21 me-cyclopen- 2.9 21 2-methyl 1- 1.6 tane butene 22 ethylbenzene 2.8 22 propene 1.5 23 o-xylene 2.8 23 2-methyl hex- 1.4 ane 24 3-me-hexane 2.6 24 n-pentane 1.4 25 2,3-dime-pen- 2.5 25 2-methyl pen- 1.2 tane lane 26 1,4-dieth-ben- 2.4 zene 27 iso-butene 2.2 28 2,2,4-trime- 2.2 pentane 29 1,2,ttrime- 2.2 pentane 30 i-butyl-benzene 2.2 31 2-me-2-butane 1.8 32 1,3,5-trime- 1.8 benzene 33 cyclopentane 1.6 235 26 o-ethyl toluene 1.0 27 ethylene 1.0 28 1-pentene 0.9 29 2,3- dim ethyl 0.8 pentane 30 ethylbenzene 0.8 31 methyl cyclo- 0.8 pentane 32 n-hexane 0.8 33 3-methyl hex- 0.7 ane
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From page 236... ...
In the urban-suburban areas, the total Propy-Equiv concentration is always less than the total VOC concentration, indicative of the large amounts of relatively unreactive VOCs typically present in the urban atmosphere. In rural areas and in the remote tropical forests, on the other hand, where emissions of highly reactive biogenic VOCs are the largest, the total Propy-Equiv concentration is always larger than the total VOC concentration.
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From page 237... ...
. od that the concentrations of VOCs in rural regions of the United States and in the remote tropical forests of Brazil are similar to those found in urban centers of the United States; the total Propy-Equiv concentrations from these three regions all range from 50 to 250 ppbC.
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From page 238... ...
For the Los Angeles sites, we used a speciated VOC inventory prepared by the California Air Resources Board (CARB) to simulate VOC emissions during an August day in the Los Angeles area (T.
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From page 239... ...
239 o c o C' A> ~ O'er ID US at A)
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From page 241... ...
Press. FIGURE ~8 Isoprene concentrations as function of temperature at Pnde, a suburb of Baton Rouge, and at the Louisiana State University campus, in down town Baton Rouge.
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From page 242... ...
The anthropogenic and biogenic contributions to the total reactivity vary significantly over the course of the day. In Baton Rouge and Glendora, anthropogenic VOCs peak in the early morning hours; biogenic VOCs tend to peak during the mid- and late afternoon.
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From page 243... ...
For instance, except for the Los Angeles sites, the splitting of anthropogenic VOCs between mobile and stationary source VOCs was based on a national rather than a local inventory. The assignment of biogenic VOCs is a lower limit because isoprene was generally the only biogenic VOC iclentified in the speciated data.
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From page 244... ...
Our analysis suggests that in many cities, even if anthropogenic VOC emissions are totally eliminated, a background of reactive biogenic VOCs will remain; on hot summer days, this background can be equivalent to 10 or 20 ppbC, or perhaps more, of propylene. Without control of NOX emissions, this VOC background should be able to generate ozone concentrations that exceed the NAAQS concentration of 120 ppb (Chameides et al., 19884.
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From page 245... ...
By contrast, our analysis based on the ambient concentrations of mobile-source and stationary-source VOCs indicates that mobile sources contribute as much as or perhaps somewhat more than stationary sources (Figures 8-9, 8-10, and 8-11~. Moreover, as illustrated in Figure 8-12, this finding appears to be essentially independent of whether the NAPAP invento
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From page 246... ...
80 70 60 c o Q <.' 50 Q Q Q ,- 40 UJ Q ° 30 20 10 · Mobile 3 Stationary ~ Biogenic O NAPAP CARB NAPAP CARB Glendore Glendora Claremont Claremont FIGURE 8-12 Nonmethane VOC Propy-Equiv concentrations in units of ppb Carbon apportioned by source category using the 1985 National Acid Precipitation Assessment Program (NAPAP) speciated VOC inventory for the nation and the California Air Resources Board (CARB)
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From page 247... ...
1 000 100 10 1 .0 0.1 0.01 Urban-suburban Hur~ . O3 = 20-40 ppbv ~ = 20-40 ppb ~1 ~ |Marine| | Remote tropical forest | 1.0 1 0 1 00 1 000 Propy-Equiv, ppbC FIGURE 8-13 VOC, NOX and ozone concentrations in the atmospheric boundary layer at four locations.
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From page 248... ...
This gradient suggests that anthropogenic sources dominate the NOx atmospheric budget in the continental United States and that the greatest domination usually occurs in urban centers. On an OH-reactivity-based scale, the VOC concentrations observed at surface sites in the remote tropical forests of Brazil, in rural areas of the eastern United States, and in urban-suburban areas of the United States are comparable.
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From page 249... ...
A more representative analysis would be possible with a more complete data base, including a more comprehensive set of VOC measurements that more accurately establishes the horizontal and vertical variability of these species in the troposphere. In addition, one cannot exclude the possibility that the VOC analysis has been significantly biased by the inability of current techniques to identify and quantify the concentrations of all VOCs in the atmosphere.
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