Weekend/Weekday Ozone Observations in the South Coast Air Basin

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• The ratios of the average 6-9 a.m. (PDT) VOC/NOx ratio on Saturday to that on Wednesday are 1.05, 1.06, 1.17, and 1.18 for the years 1981-84, 1985-89, 1990-94, and 1995-98, respectively. The corresponding Sunday/Wednesday ratios are 1.10, 1.17, 1.27 and 1.42. Similar differences are observed for the VOC/NOx ratios during the time of maximum ozone. • The average weekday 6-9 a.m. (PDT) VOC/NOx ratios during the 1990s are about 7 compared to 8-9 on Saturdays and 9-10 on Sundays, and the ratios at maximum ozone are 10-11 on weekdays, 12-13 on Saturdays and 13-14 on Sundays. • The morning VOC/NOx ratios are above the ridgeline in the ozone isopleth plot or VOClimited during weekdays and move toward the ridgeline on weekends. While greater carryover of VOC on weekends contributes to greater weekend morning VOC/NOx ratios, most of the increase is due to lower NO emissions during weekend mornings. 2-8
Table 2-1 Air Quality Parameters for the Conceptual Explanation of the Weekend Effect 2 No. Parameter Purpose 1 [O 3 ]max (ppb) WE/WD effect indicator 2 4-5 PDT [NO] (ppb) Carryover 3 4-5 PDT [NO2] (ppb) Carryover 4 4-5 PDT [NO2]/[NOx] (ppb) Carryover 5 4-5 PDT [NMHC] (ppbC) Carryover (via Bendix or regression with CO) 6 7-8 PDT [NO] (ppb) Ozone titration potential (morning rush hour) 7 7-8 PDT [NO2] (ppb) For NO 2 -NO comparison 8 7-8 PDT [CO] (ppm) Surrogate for gas-powered morning emissions 9 7-8 PDT [NMHC] (ppbC) Fresh emissions (morning rush hour) 10 6-9 PDT NMHC/NOx Reaction efficiency/rate for morning commute 11 tNO=O3 (PST) Interpolated time of morning crossover of O 3 and NO. Marks ends of O 3 inhibition period and the beginning of the ozone accumulation period. 12 tO3max (PST) Interpolated time of daily maximum O 3 13 tO3max-tNO=O3 Duration of O 3 accumulation 14 O 3 rate (ppb/hour) Rate of O 3 accumulation (see definition below) 15 NMHC/NOx(t O3max ) Reaction efficiency/rate at t O3max Rate of O3 accumulation: ([O3]max-[O3(tNO=O3)])/(tO3max-tNO=O3) 2 Data are tabulated in Appendix A of Fujita et al. (2000b). 2-9
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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
Page 17 and 18: 1. STUDY PERSPECTIVE AND SUMMARY Th
Page 19 and 20: 40 percent. Consequently, the contr
Page 21 and 22: dioxide (NO 2 ) 4 , and carbon mono
Page 23 and 24: and upwind samples before and after
Page 25 and 26: where J 1 is the photolysis frequen
Page 27 and 28: transported from an urban center to
Page 29 and 30: of the week on Friday and Saturday.
Page 31 and 32: VOC reactivity, photochemical aging
Page 33 and 34: corresponding source attributions a
Page 35 and 36: multiplicative constant. This const
Page 37 and 38: Table 1.4-1 Trends in Duration and
Page 39 and 40: Table 1.4-3 Regression Statistics f
Page 41 and 42: O 3 Ozone Formation Chemistry NO 2
Page 43 and 44: 200 1981-84 200 1995-98 160 160 120
Page 45 and 46: 100 NO 1000 NMHC (estimated from CO
Page 47 and 48: 5 Sunday - Wednesday (1981-84) 10 T
Page 49 and 50: 10.0 8.0 NMHC/NOx 6.0 4.0 2.0 0.0 S
Page 51 and 52: Ratio of Peak Ozone to Potential Oz
Page 53 and 54: Nitrogen Oxides at Azusa, 9/30/00 t
Page 55 and 56: Ambient NOx Associated with CO and
Page 57 and 58: Source Contribution Estimate (ug/m3
Page 59 and 60: 2.8 2.6 Ozone (ppb) 2.4 log NOx (pp
Page 61 and 62: 2. EVOLUTION OF THE OZONE EFFECT IN
Page 63 and 64: the SoCAB has dropped sharply as sh
Page 65 and 66: the duration of ozone accumulation,
Page 67: • NO 2 concentrations and NO 2 /N
Page 71 and 72: 0.18 Azusa, Summer 1995 12.0 0.15 1
Page 73 and 74: 250 200 150 100 50 0 1976 1977 1978
Page 75 and 76: 80 1981-84 60 40 20 0 80 Sun Mon Tu
Page 77 and 78: 1.00 1981-84 0.80 0.60 0.40 0.20 0.
Page 79 and 80: 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
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160 140 Upland - Saturdays mean Ozo
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maximum 1hour ozone (ppb) 100 90 80
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NMHC/NOx ratio 14 12 10 8 6 4 2 0 S
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Los Angeles - N. Main Azusa 140 140
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Los Angeles - N. Main Azusa 140 140
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2.8 2.6 PAN (ppb) 2.8 2.6 HCHO (ppb
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NO2 Photolysis Rate Parameter 0.35
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4. WEEKDAY VARIATIONS IN THE SOURCE
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9 a.m. andnoon. Sampling was conduc
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interfaced to an Entech model 7100
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values measured at the regional sit
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into a category named "UNID." The s
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more than a few percent of the tota
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period, the amount of NOx associate
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weekend/weekday differences during
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• Day-of-the-week changes in the
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Table 4.4-1 Default Source Composit
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Table 4.4-1a Number of observations
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Table 4.4-1c Number of observations
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Table 4.4-2a Number of observations
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Table 4.4-2c Number of observations
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Table 4.4-3a CMB Performance Parame
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Table 4.4-3c Source Contribution Es
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Table 4.5-2 Weekend/Weekday Differe
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800 700 600 Wednesday NO and NOy (p
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Estimated NOx Estimated NOx (ppb) 5
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VOC/NOx Ratios 6.0 5.0 4.0 Mon, 10/
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Nitrogen Oxides at Azusa 80 60 02-0
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Nitrogen Oxides at Pico Rivera 180
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Nonmethane Organic Gas at Azusa 500
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Nonmethane Organic Gas at Pico Rive
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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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Ambient NOx Associated with CO and
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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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