Weekend/Weekday Ozone Observations in the South Coast Air Basin

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1.0 Sundays mean potential Ozone fraction =([O3]/([O3]+[NOx]) 0.8 0.6 0.4 0.2 0.0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 HOUR (PDT) mean potential Ozone fraction =([O3]/([O3]+[NOx]) 1.0 0.8 0.6 0.4 0.2 Saturdays 0.0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 HOUR (PDT) mean potential Ozone fraction =([O3]/([O3]+[NOx]) 1.0 0.8 0.6 0.4 0.2 Weekdays (Tues-Thur) 0.0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 HOUR (PDT) 80-85 86-90 91-94 95-98 99-00 Figure 3.6-2. Diurnal variations in the ratios of ozone to potential ozone (O 3 + NOx) on Sundays, Saturdays, and weekdays at Azusa for the years 1980-85, 1986-1990, 1991-1994, 1995-1998, and 1999-2000. 3-36
4. WEEKDAY VARIATIONS IN THE SOURCE APPORTIONMENT OF OZONE PRECURSORS This section examines the attribution of ambient NOx and VOC to emission sources with particular focus on the relative contributions of on-road diesel-powered and gasoline-powered vehicles. Multiple linear regression and Chemical Mass Balance (CMB) were used to derive approximate attributions of NOx to gasoline and diesel exhaust. CMB was used to determine the diurnal variations in source attributions of ambient VOC by day-of-the-week. A field measurement program was conducted from September 30, 2000 through October 8, 2000 to collect and assemble air quality and emission activity databases to examine relationships between emissions sources and the diurnal and day-of-the-week variations in CO, NO, NOx, VOC, VOC/NOx and NO 2 /NOx. The field study measurements focused on attribution of ambient precursor concentrations to major sources of VOC and NOx. The field measurements involved mobile sampling during periods that coincide with overnight carryover of ozone precursors, ozone inhibition, and ozone accumulation plus supplemental measurements at existing SCAQMD monitoring sites. A mobile sampling van was used to collect data to characterize the diurnal variations in relative contributions of gasoline and diesel vehicles to the ambient level of ozone precursors by day of the week. Primary pollutants (CO, NO, black carbon [BC], and speciated hydrocarbons) were measured simultaneously in the mobile van along several freeway and surface-street loops and at several regional/background locations during the carry over, ozone inhibition, and ozone accumulation periods. For each loop, the time series of NO and CO were related to indicators of compression-ignition exhaust (black carbon and heavy hydrocarbons) and spark-ignition exhaust (CO and MTBE) for the carry over, ozone inhibition, and ozone accumulation period by day of the week. The premise of this approach is that gasoline exhaust is enriched in CO and MTBE relative to diesel exhaust while diesel exhaust is enriched in black carbon and heavy hydrocarbons (nC 10 -nC 15 ) relative to gasoline exhaust. Multiple regression was used to estimate the amounts of NOx associated with CO and MTBE relative to the NOx associated with black carbon and nC 10 -nC 15 . Diurnal and day-of-the-week variations in the associations of NOx to primary pollutants are correlated to the relative contributions of diesel and gasoline exhaust to ambient NOx. These variations are examined for a variety of sampling locations, which included freeways and surface streets with varying ratios of gasoline- and diesel-powered vehicles, district monitoring stations, and other regional and background sites. The source contributions of gasoline engine exhaust and diesel engine exhaust to NMHC and NOx were estimated by Chemical Mass Balance (CMB) receptor modeling. Source composition profiles were derived for diesel and gasoline exhaust from samples collected at a truck stop and on a stretch of the 110 Freeway where heavy trucks are prohibited. Source profiles were also developed from analysis of gasoline and diesel fuel samples. In addition to the relative contributions of gasoline and diesel exhaust, the detailed speciation of VOC from the mobile sampling and the time-resolved VOC speciation at Los Angeles, Azusa, and Pico Rivera monitoring stations provided source attribution of other sources of VOC by time of day and dayof-the-week. These analyses address questions regarding the source contributions to VOC carried over from the previous evening and the relative importance of on-road versus other area sources on the diurnal variations of VOC/NOx ratios. Diurnal variations in VOC composition were also used to examine day-of-the-week differences in ozone formation potential and reactivity of the 4-1
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WEEKEND/WEEKDAY OZONE OBSERVATIONS
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obtained by DRI from the Phase II f
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TABLE OF CONTENTS Preface..........
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Table No. Table 1.4-1 Table 1.4-2 T
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periods by day-of-week at Los Angel
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Figure 1.4-13. Hourly average nitro
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Figure 3.1-2 Mean day-of-the-week v
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Figure 4.4-1b. Mean estimated sourc
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1. STUDY PERSPECTIVE AND SUMMARY Th
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40 percent. Consequently, the contr
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dioxide (NO 2 ) 4 , and carbon mono
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and upwind samples before and after
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where J 1 is the photolysis frequen
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transported from an urban center to
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of the week on Friday and Saturday.
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VOC reactivity, photochemical aging
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corresponding source attributions a
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multiplicative constant. This const
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Table 1.4-1 Trends in Duration and
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Table 1.4-3 Regression Statistics f
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O 3 Ozone Formation Chemistry NO 2
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200 1981-84 200 1995-98 160 160 120
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100 NO 1000 NMHC (estimated from CO
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5 Sunday - Wednesday (1981-84) 10 T
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10.0 8.0 NMHC/NOx 6.0 4.0 2.0 0.0 S
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Ratio of Peak Ozone to Potential Oz
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Nitrogen Oxides at Azusa, 9/30/00 t
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Ambient NOx Associated with CO and
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Source Contribution Estimate (ug/m3
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2.8 2.6 Ozone (ppb) 2.4 log NOx (pp
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2. EVOLUTION OF THE OZONE EFFECT IN
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the SoCAB has dropped sharply as sh
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the duration of ozone accumulation,
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• NO 2 concentrations and NO 2 /N
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Table 2-1 Air Quality Parameters fo
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0.18 Azusa, Summer 1995 12.0 0.15 1
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250 200 150 100 50 0 1976 1977 1978
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80 1981-84 60 40 20 0 80 Sun Mon Tu
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1.00 1981-84 0.80 0.60 0.40 0.20 0.
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160 1981-84 120 80 40 0 160 Sun Mon
Page 81 and 82: 5.0 1981-84 4.0 3.0 2.0 1.0 0.0 5.0
Page 83 and 84: 12.00 1981-84 11.00 10.00 9.00 8.00
Page 85 and 86: NMHC (ppbC) 1000 800 600 400 200 4-
Page 87 and 88: 10.00 1981-84 8.00 6.00 4.00 2.00 0
Page 89 and 90: Sunday 1981-84 Time (PDT) 16 15 14
Page 91 and 92: 16 Sunday 1990-94 35 Time (PDT) 15
Page 93 and 94: 40 Sunday O3 Accumulation Rate (ppb
Page 95 and 96: 15.0 1981-84 12.0 9.0 6.0 3.0 0.0 1
Page 97 and 98: 3. CHARACTERIZATION OF THE CURRENT
Page 99 and 100: 3.2 Weekday Differences in Diurnal
Page 101 and 102: timing hypothesis, which requires a
Page 103 and 104: through the conversion of NO to NO
Page 105 and 106: Weekday Differences in Diurnal Vari
Page 107 and 108: activity including [HNO 3 ]/[H 2 O
Page 109 and 110: Table 3.2-1 Day-of-the-Week Variati
Page 115 and 116: Table 3.3-1b Day-of-the-Week Differ
Page 117 and 118: 120 Los Angeles - N. Main - Saturda
Page 119 and 120: 160 140 Upland - Saturdays mean Ozo
Page 121 and 122: maximum 1hour ozone (ppb) 100 90 80
Page 123 and 124: NMHC/NOx ratio 14 12 10 8 6 4 2 0 S
Page 125 and 126: Los Angeles - N. Main Azusa 140 140
Page 127 and 128: Los Angeles - N. Main Azusa 140 140
Page 129 and 130: 2.8 2.6 PAN (ppb) 2.8 2.6 HCHO (ppb
Page 131: NO2 Photolysis Rate Parameter 0.35
Page 135 and 136: 9 a.m. andnoon. Sampling was conduc
Page 137 and 138: interfaced to an Entech model 7100
Page 139 and 140: values measured at the regional sit
Page 141 and 142: into a category named "UNID." The s
Page 143 and 144: more than a few percent of the tota
Page 145 and 146: period, the amount of NOx associate
Page 147 and 148: weekend/weekday differences during
Page 149 and 150: • Day-of-the-week changes in the
Page 151 and 152: Table 4.4-1 Default Source Composit
Page 153 and 154: Table 4.4-1a Number of observations
Page 155 and 156: Table 4.4-1c Number of observations
Page 157 and 158: Table 4.4-2a Number of observations
Page 159 and 160: Table 4.4-2c Number of observations
Page 161 and 162: Table 4.4-3a CMB Performance Parame
Page 163 and 164: Table 4.4-3c Source Contribution Es
Page 165 and 166: Table 4.5-2 Weekend/Weekday Differe
Page 167 and 168: 800 700 600 Wednesday NO and NOy (p
Page 169 and 170: Estimated NOx Estimated NOx (ppb) 5
Page 171 and 172: VOC/NOx Ratios 6.0 5.0 4.0 Mon, 10/
Page 173 and 174: Nitrogen Oxides at Azusa 80 60 02-0
Page 175 and 176: Nitrogen Oxides at Pico Rivera 180
Page 177 and 178: Nonmethane Organic Gas at Azusa 500
Page 179 and 180: Nonmethane Organic Gas at Pico Rive
Page 181 and 182: NMOG/NOx Ratios at Azusa 20 15 02-0
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estimated contribution by source (u
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500 Nonmethane Hydrocarbons 400 NMH
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5 Azusa, Weekdays 6-9 a.m (10/2/00-
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2.0 Azusa, Weekdays 6-9 a.m (10/2/0
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Pico Rivera 150 120 BC-Associated C
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Nitrogen Oxides 800.00 700.00 600.0
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5. REFERENCES Altshuler, S.L., T.D.
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Fujita, E.M., J.G. Watson, J.C. Cho
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Roberts, J.M. (1983) Measurements o
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Weekend/Weekday Ozone Observations in the South Coast Air Basin

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