Weekend/Weekday Ozone Observations in the South Coast Air Basin

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HO and HO 2 the contour plots were made for solar noon while all other plots were made for sunset of the first simulated day. 1.4 Results and Discussion The weekend ozone effect is rooted in ozone’s complex photochemistry, and arises from the day-of-the-week differences in the temporal and spatial patterns of VOC and NOx emissions. These emission-activity differences alter the diurnal and spatial variations in VOC and NOx concentrations and VOC/NOx ratios, which affect the diurnal evolution of ozone chemistry. Day-of-the-week differences in the concentrations of ozone were examined with respect to its diurnal patterns, the diurnal patterns of NO, ratios of peak ozone to potential ozone, VOC reactivity, photochemical aging, and NO 2 photolysis rates. The results of these analyses were synthesized with the fundamental knowledge of ozone formation, theoretical analysis of ozone and its precursors, and time-variations in the source contributions of VOC and NOx to develop a self-consistent explanation for the weekend ozone effect. 1.4.1 Fundamentals of Ozone Formations The chemistry of ozone formation is well established. Ozone is produced in the atmosphere by the reaction of a ground state oxygen atom, O ( 3 P), and molecular oxygen (O 2 ). While O 2 is abundant in the atmosphere, free oxygen atoms are not. At lower altitudes, where only UV radiation with wavelengths greater than 280 nm is present, the only significant net oxygen atom production is from photodissociation of NO 2 into NO and ground state oxygen atoms, Reaction (1). The ground state oxygen atoms react with molecular oxygen to produce O 3 , Reaction (2), (where M is a third body such as N 2 or O 2 ). NO 2 + hν → NO + O( 3 P) (1) O( 3 P) + O 2 + M → O 3 + M (2) When nitric oxide molecules are present, O 3 reacts rapidly with NO to regenerate NO 2 , Reaction (3). O 3 + NO → NO 2 + O 2 (3) The first and third reactions occur rapidly, establishing a steady-state equilibrium ozone concentration [O 3 ] that is determined by the "NO-photostationary state equation," Equation (4) [O 3 ] = J 1[NO 2 ] k 3 [NO] (4) 1-8
where J 1 is the photolysis frequency of Reaction (1), k 3 is the rate constant for Reaction (3), [NO 2 ] is the concentration of nitrogen dioxide and [NO] is the concentration of nitric oxide. Because these reactions only recycle O 3 and NO x , they are insufficient, by themselves, to create excessive ozone levels. When carbon monoxide or volatile organic compounds are present, however, their oxidation produces the hydroperoxy radical (HO 2 ) and organic peroxy radicals (RO 2 ), which react with NO to form NO 2 without destruction of ozone, thereby allowing ozone to accumulate. The hydroxyl radical (HO) initiates the oxidation of VOCs that form the peroxy radicals. A fraction of O 3 photolyzes to produce an excited oxygen atom, O( 1 D), Reaction (5), which reacts with water to produce hydroxyl (HO) radicals, Reaction (6). O 3 + hν → O( 1 D) + O 2 (5) O( 1 D) + H 2 O → 2 HO (6) Other sources of HOx radicals include the photolysis of carbonyl compounds and smaller contributions due to nitrous acid (HONO) and other radical precursors. The HO radicals react with CO or organic compounds (RH) to produce peroxy radicals (HO 2 or RO 2 ). The peroxy radicals react with NO to produce NO 2 which photolyzes to produce additional O 3 : CO + HO (+O 2 ) → CO 2 + HO 2 (7) RH + HO → R + H 2 O (8) R + O 2 + M → RO 2 + M (9) RO 2 + NO → RO + NO 2 (10) RO + O 2 → HO 2 + CARB (11) HO 2 + NO → HO + NO 2 (12) The net reaction is the sum of Reactions (8) through (12) plus twice Reactions (1) and (2): RH + 4 O 2 + 2 hν → CARB + H 2 O + 2 O 3 (13) where CARB is a carbonyl species, either an aldehyde (R'CHO) or a ketone (R'CR''O). The carbonyl compounds may further react with HO or they may photolyze to produce additional peroxy radicals that react with NO to produce NO 2 (Seinfeld, 1986; Finlayson-Pitts and Pitts, 1986). Peroxy radical reactions with NO reduce the concentration of NO and increase the concentration of NO 2 . This reduces the rate of Reaction (3), which destroys O 3 and increases the rate of reaction (1), which eventually produces ozone. The increase in [NO 2 ]/[NO] ratio leads to higher O 3 concentration according to Equation (4). 1-9
Page 1 and 2: WEEKEND/WEEKDAY OZONE OBSERVATIONS
Page 3 and 4: obtained by DRI from the Phase II f
Page 5 and 6: TABLE OF CONTENTS Preface..........
Page 7 and 8: Table No. Table 1.4-1 Table 1.4-2 T
Page 9 and 10: periods by day-of-week at Los Angel
Page 11 and 12: Figure 1.4-13. Hourly average nitro
Page 13 and 14: Figure 3.1-2 Mean day-of-the-week v
Page 15 and 16: 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 upwind samples before and after
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 and 68: • NO 2 concentrations and NO 2 /N
Page 69 and 70: Table 2-1 Air Quality Parameters fo
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
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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
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Sunday 1981-84 Time (PDT) 16 15 14
Page 91 and 92:
16 Sunday 1990-94 35 Time (PDT) 15
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40 Sunday O3 Accumulation Rate (ppb
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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
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Weekday Differences in Diurnal Vari
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activity including [HNO 3 ]/[H 2 O
Page 109 and 110:
Table 3.2-1 Day-of-the-Week Variati
Page 111 and 112:
Page 113 and 114:
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 and 132:
NO2 Photolysis Rate Parameter 0.35
Page 133 and 134:
4. WEEKDAY VARIATIONS IN THE SOURCE
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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
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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
Page 185 and 186:
500 Nonmethane Hydrocarbons 400 NMH
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5 Azusa, Weekdays 6-9 a.m (10/2/00-
Page 189 and 190:
2.0 Azusa, Weekdays 6-9 a.m (10/2/0
Page 191 and 192:
Ambient NOx Associated with CO and
Page 193 and 194:
Page 195 and 196:
Page 197 and 198:
Pico Rivera 150 120 BC-Associated C
Page 199 and 200:
Nitrogen Oxides 800.00 700.00 600.0
Page 201 and 202:
5. REFERENCES Altshuler, S.L., T.D.
Page 203 and 204:
Fujita, E.M., J.G. Watson, J.C. Cho
Page 205 and 206:
Roberts, J.M. (1983) Measurements o
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Weekend/Weekday Ozone Observations in the South Coast Air Basin

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