Episodic ozone air quality in Jakarta in relation to meteorological conditions

Atmospheric Environment 42 (2008) 6806–6815

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Episodic ozone air quality in Jakarta in relation to meteorological conditions Didin Agustian Permadi, Nguyen Thi Kim Oanh* Environmental Engineering and Management, SERD, Asian Institute of Technology, P.O. Box 4, Klong Luang, Pathumthani 12120, Thailand

a r t i c l e i n f o

a b s t r a c t

Article history: Received 5 February 2008 Received in revised form 4 May 2008 Accepted 6 May 2008

Surface O3 air quality in Jakarta, Indonesia, was analyzed using hourly monitoring data during January 2002–March 2004 from the five automatic monitoring stations with the aim to provide the first insight into the ozone formation and accumulation leading to the high ozone levels over the city. The city location near the equator with the intensive emission sources is of especial interest in this regard. The surface O3 levels in Jakarta were high which frequently exceeded the hourly national ambient air quality standard (120 ppb), i.e. over 450 hourly measurements in 2002 and 2003 or 0.7% over 66,000 hourly ozone measurements at the five stations during 2002–2003. The monthly average of O3 was maximum in October and minimum in February. Selected days of episodic high O3 in April, May, and October, and low ozone days in February were comparatively analyzed in relation to local and synoptic meteorological conditions. The high ozone days were characterized by more intense solar radiation, higher temperature, and lighter surface wind which are favorable for photochemical production of O3. Low pressure gradients on synoptic charts of the high ozone days linked to the low wind and more stagnant air that are favorable for ozone build-up over the city. Further studies, including photochemical modeling, are required to understand better the conditions leading to high ozone in the city in order to formulate the ozone management strategies. Ó 2008 Elsevier Ltd. All rights reserved.

Keywords: Surface ozone Episode Meteorology Hotspots Indonesia

1. Introduction Jakarta is the capital city of Indonesia which has 661 km2 of land area and is inhabited by approximately 8.7 million people (JBS, 2006). It is located in a low land area with average height of around 7 m above the sea level and centered at 6120 South latitude and 106 480 East longitude. The climate in the city is characterized by monsoons which bring about two major seasons, the dry (centered in September–November) and wet (centered in January– March). In the dry season the southeasterly (SE) monsoon dominates while in the wet season the northwesterly (NW) wind dominates (Sofyan et al., 2007). The intensive industrialization, urbanization, and economic development in the city have led to serious air * Corresponding author. Tel.: þ662 524 5641. E-mail address: [email protected] (N.T. Kim Oanh). 1352-2310/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2008.05.014

pollution problems. The measured air pollutants (CO, NO, SO2, PM10 and O3) frequently exceed the National Ambient Air Quality Standard (NAAQS) at various air quality monitoring sites (Shanty et al., 2002). This was largely due to high emission from large vehicle fleets, especially with high traffic congestion. Jakarta EPA (2004) reported that ozone (O3) is one of the two pollutants (PM10 is the other) that cause the air pollution standard index (PSI) to be above the unhealthy level of 100. Surface O3 becomes a major environmental concern because of its adverse impacts on human health, crops and forest ecosystems (Sillman, 1999). O3 has been extensively studied in developed countries but less in tropical Asia (Zhang and Kim Oanh, 2002; Mittal et al., 2007). Extensive monitoring and modeling applications are normally required to understand the complex processes involved in ozone formation and build-up over a location. Specifically, surface O3 formation is a highly non-linear

D.A. Permadi, N.T. Kim Oanh / Atmospheric Environment 42 (2008) 6806–6815

process in relation to the precursors (NOx and VOCs) and is strongly influenced by the meteorological conditions. It has been shown that, under some atmospheric conditions, the O3 formation is mainly affected by NOx, while in other conditions, O3 production is mainly affected by VOCs. This non-linear relationship is frequently represented by such a diagram which plots contour of O3 concentrations as a function of VOC and NOx concentrations (Seinfeld and Pandis, 1998). Ozone in Jakarta is of research interest primarily because of its near-equatorial location, where abundance of sunshine and high temperature would enhance the O3 formation. A previous study on O3 air quality in Jakarta using the intermittent O3 monitoring data collected by Jakarta Environmental Protection Agency (JEPA) before 2002 has identified the lack of systematic monitoring data as the main barrier to in-depth understanding of the ozone pollution situation (Shanty et al., 2002). Since 2002, additional five automatic monitoring stations (JAF1–JAF5) have been operating by JEPA. This work, therefore, attempts to analyze the status of ozone air quality in Jakarta using the newly generated continuous monitoring records with a focus on the conditions leading to episodic high ozone levels in the city.

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space of mixed land use including the commercial facilities and residential areas. Both JAF4 and JAF5 are located near the city center with dense population and traffic roads: JAF5 is in the city park inside the Senayan Sport Complex Stadium while JAF4 is in a municipality building complex. Detail information of each monitoring station is given in Table S1, Supplementary information. 3. Data analysis Hourly (rolling average) ozone concentrations were estimated from the 30-min data record to compare with the hourly NAAQS of 120 ppb. The episodes were identified based on the daily maximum hourly O3 concentrations which exceeded the NAAQS for at least two consecutive hours per day at more than one monitoring stations. Synoptic and local meteorological conditions were comparably analyzed for episodic (high O3) and non-episodic (low O3). The monitored data of NOx and CO, were analyzed to reveal the relationship between O3 and its major precursors. 4. Results and discussion 4.1. Status of O3 air quality in Jakarta

2. Monitoring data The air quality monitoring network of Jakarta is operated by JEPA and includes both manual and automatic monitoring stations. The intermittent manual monitoring has been initiated since 1986 at 12 monitoring sites which were operated on a rotational basis. Each station measures selected air pollutants for 24-h every 8 days (Shanty et al., 2002). Since early 2002, the continuous monitoring of the ambient quality has started at five JEPA automatic monitoring stations (JAF1–JAF5). All of these automatic monitoring stations are equipped to monitor CO, NO, NO2, SO2, PM10 and O3 and the meteorology (wind speed and direction, temperature, relative humidity and global radiation) producing 30-min average data online. Methane (CH4) and NMHC (non-methane hydrocarbons) are not monitored at any station, which prevent an in-depth analysis of O3 precursors in the city. The instruments used for the monitoring parameters discussed in this paper include CO analyzer (Horiba-APMA360), NO and NO2 analyzer (Horiba-APNA360), ozone analyzer (Horiba-APOA36) and meteorological sensors for wind, temperature, and global radiation star pyranometer. The operation and maintenance of the stations are handled by the Regional Center (RC) in JEPA that calibrates the equipment once per year. In addition, as a way of Quality Assurance (QA)/Quality Control (QC), in this paper we examine the consistency of monitoring data including diurnal variation of pollutants, the comparability with published patterns in other SEA countries, and consistency with meteorology (wind direction, wind velocity, synoptic scale). All these five stations are classified as the general ambient stations which are not located at the curbside of main roads. Accordingly, JAF1 is located at a dense residential area while JAF2 is located near the commercial area and between the office buildings. JAF3 is located in an open

The maximum hourly ozone concentrations at all stations during the study period 2002–2003 were well above the NAAQS for O3 (120 ppb) as presented in Table 1. Note that in 2002 the temporal completeness of the data records was satisfactory at all five stations with the lowest completeness at JAF2 (211/365) while in 2003 the frequent missing data were observed at JAF3 and JAF2 where the completeness was 97/365 and 190/365, respectively. In 2002, three stations (JAF3–JAF5) located on the southwest (SW) of the city center have a high frequency of exceeding the NAAQS producing higher numbers of hours/days of high ozone (Table 1) as compared to JAF1 (with almost the same temporal completeness of data record) which is located on the northeast (NE) to the city center (Fig. S1, Supplementary information). Similar observation is for 2003 when the highest O3 level (356 ppb) and highest frequency of exceeding NAASQ was revealed at JAF5. In total during 2002–2003, at five monitoring stations hourly ozone of above 120 ppb was observed for 452 h (0.7% over 66,000 hourly ozone measurements at the five stations during 2002–2003) and the highest frequency of exceeding standard was for JAF5, 147 h over the 2 years. For the prevalent SE monsoon over the city during the dry season (when high ozone observed during a year) JAF3, JAF4 and JAF5 are located downwind of the city center which may justify the higher level of O3 observed at these stations. It was observed that in 2002 the number of hours of high ozone (328 h) in Jakarta was significantly higher than 2003 (124 h). The less completeness of the data in 2003 may partly be a reason for this. In addition, it is noted that the El Nino event occurred in 2002 (NCDC, 2005) would result in less rainfall, drought and stable atmosphere in Southeast Asia (Lawrence et al., 2001) hence may lead to abnormally high ozone levels in Jakarta. For example, in

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D.A. Permadi, N.T. Kim Oanh / Atmospheric Environment 42 (2008) 6806–6815

Table 1 Summary of hourly O3 air quality in Jakarta during 2002–2003 Station

2002 Hoursa

JAF JAF JAF JAF JAF

2003 High O3 daysb

Total monitored daysc

1 2 3 4 5

21 18 118 103 68

13 8 56 48 39

319 211 327 358 348

Total

328

164

1563

Max 1 h-O3 (ppb) 274 149 202 181 243

Hoursa

High O3 daysb

Total monitored daysc

16 0 8 21 79

12 0 3 12 47

331 190 97 348 348

124

74

1314

Max 1 h-O3 (ppb) 140 113 150 151 356

Total hours exceeding NAAQS

37 18 126 124 147 452

JAF 1, 4, 5: more complete record. JAF 3: missing data in July–December 2003. JAF 2: missing data in September–November 2003. a Number of hours exceeding the 1 h-O3 NAAQS of 120 ppb. b Days with at least one ozone measurement exceeding NAAQS. c Days with available monitoring data record.

Hanoi of Vietnam in 2002 the observed mean (23 ppb) and hourly maximum (98 ppb) of 1-hr O3 were higher than the corresponding values in a normal year of 2003 (96 ppb and 13 ppb, respectively) as reported by Long (2006). Similarly, higher hourly maximum ozone of 165 ppb and annual average of 18.9 ppb were observed in northern of Thailand in 2002 as compared to 104 ppb and 18.5, respectively, in 2003. In Bangkok, at ambient stations, the maximum hourly of 175 ppb and annual average of 14.5 ppb were observed in 2002 which actually were lower than that of 2003 (187 ppb and 16.2 ppb) (Nghiem, 2008). Perhaps, fast increase in the source emission would be a more determining factor for ozone fluctuation in Bangkok than the weak El Nino effects of 2002, but further research would be required to confirm this hypothesis. 4.2. Monthly variation of O3 in Jakarta and local meteorology Monthly variations of O3 concentrations and meteorological conditions (wind speed, temperature and global radiation) were analyzed using the monitoring data at three ambient stations where more complete data record was available (JAF1, JAF4 and JAF5). The monthly average of hourly O3 was found to depend strongly on local meteorological conditions. The highest ozone was in October, which is the middle of dry season, with averaged values of 39 ppb in 2002 and 37 ppb in 2003 (Fig. 1). During the dry season (September–November), higher temperature (28–29  C), daytime hourly average global radiation (305–374 W m2) and lower wind speed (1–1.6 m s1) would enhance the formation and accumulation of ozone (Zhang and Kim Oanh, 2002; Peter and Law, 2001) over the city. The lowest monthly O3 are detected in January– February period (averaged values of 16–24 ppb) which coincides with the rainy season with the highest rainfall (e.g. 280 mm month1 for January 2004), lower temperature and generally higher wind speed. Correlations between hourly ozone concentrations and wind speed, temperature, global radiation, respectively, were estimated for the data set combining all the simultaneous measurements at each of three stations, which yielded the correlation coefficient (r) of 0.323, 0.311, and 0.263,

respectively, all significant at the 0.01 level (two-tailed bivariate correlation analysis). 4.3. Diurnal variation of O3 Diurnal variations of O3, NO, NO2 and CO at the 3 stations (JAF1, JAF4 and JAF5) for each month were analyzed which show typical patterns for large polluted cities (Lam et al., 2001; Zhang and Kim Oanh, 2002; Chan and Yao, 2007). Detail for February (minimum O3), April, May and October (high O3) is presented in Fig. 2. Basically, the highest CO and NO were observed at morning rush hours (around 7:00) while NO2 was peaked around 1 h later reflecting the time period required for the NO to NO2 conversion. The daily peak O3 was observed from 11:00– 13:00 with a maximum at 11:00–12:00 which is similar to that reported in Nugroho et al. (2006) who analyzed ozone measured by a mobile station in Jakarta during 2003. The mobile station data are not included in our study due to its non-fixed location. The appearance of the daily maximum in Jakarta is generally earlier than Bangkok, 13–15:00 (Zhang and Kim Oanh, 2002), or Hong Kong, 14:00–16:00 (Lee et al., 2002), which may be due to the Jakarta’s lower latitude that has the GR peaks generally at 10–12:00 as compared to 13–14:00 in Bangkok, for example. The photochemical build-up of surface O3 in Jakarta is much more significant during the dry season (October) than the rainy season (February) with the difference between daytime and nighttime O3 monthly means of about 10–15 ppb in February and 40–80 ppb in October. The later is higher than the reported values of 10–20 ppb for Hong Kong (Lam et al., 2001). 4.4. Emission sources of ozone precursors in Jakarta The high concentrations during morning peak hours reflect the high traffic emission in the city. Especially, the development of large-scale housing projects around the city has intensified the daily traffic flows between the fringe areas and the central part of Jakarta. There was no significant difference between February and October morning peaks’ levels of CO and NO. For example, at JAF1 in February

D.A. Permadi, N.T. Kim Oanh / Atmospheric Environment 42 (2008) 6806–6815

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Prevalent wind direction (24 H) 3 2.5 2 1.5 1 0.5

Wind speed (m s-1)

0 01-2002 02-2002 03-2002 04-2002 05-2002 06-2002 07-2002 08-2002 09-2002 10-2002 11-2002 12-2002 01-2003 02-2003 03-2003 04-2003 05-2003 06-2003 07-2003 08-2003 09-2003 10-2003 11-2003 12-2003 01-2004 02-2004 03-2004

Ozone (ppb)

NW NW NW SW SE SE SE SE SW NE SW SW SW SW SW SW SW SE SE SE SE SW SW SW NW SW SW

45 40 35 30 25 20 15 10 5 0

Ozone

Wind speed

Prevalent wind direction (day time) NW SW NW SW SE NE NE NE SW SW SW SW SW SW SW SW SW SE SE NE SE SW SW SW SW SW SW

300 250 200 150 100 50 0 01-2002 02-2002 03-2002 04-2002 05-2002 06-2002 07-2002 08-2002 09-2002 10-2002 11-2002 12-2002 01-2003 02-2003 03-2003 04-2003 05-2003 06-2003 07-2003 08-2003 09-2003 10-2003 11-2003 12-2003 01-2004 02-2004 03-2004

Glob Rad (W m-2) Rainfall (mm month-1)

350

Temperature (deg C)

29.5 29 28.5 28 27.5 27 26.5 26 25.5 25

400

Glob Rad

Rainfall

Temperature

Fig. 1. Monthly average of (diurnal and/or daytime only) ozone and meteorological variables during January 2002–March 2004.

morning peaks CO was 2.3 ppb and NO was 34 ppb, as compared to the corresponding values in October of 2.4 ppb for CO and 38 ppb for NO (Fig. 2). Given a better atmospheric mixing condition in the wet season (at least higher wind speed) somewhat lower ambient pollutants concentrations would be expected from the same emission intensity. These together suggest that the traffic is the major source of the pollutants in the city all year around (both dry and wet seasons). It is noted that the evening peaks of CO and NO appeared quite late (21–22:00) and were even higher than the morning peaks, which may be due to both the restriction in vertical mixing and increased emission sources (cooking) in the evening hours in Jakarta. Biomass open burning could also be another important source of ozone precursors affecting Jakarta but the contribution would be predominant only during the dry season. In fact, burning activities may emit a significant amount of VOC, NOx, and CO. Fire has been a traditional means to clear land for agricultural production in Indonesia. It is believed to be the cheapest way to improve the soil structure, to reduce weed and plant re-growth, and to control pests and diseases (Ketterings et al., 1999). The traditional slash and burning (S&B) method is commonly used. Farmers generally start slashing in March and burning in August which may last for a few months (Ketterings et al., 1999). Intensive biomass burning toward the end of dry

season would potentially contribute a large amount of precursors to maximize ozone in this period. In an attempt to qualitatively discuss the effect of biomass burning on ozone air quality, the daily counts of hotspots were obtained from the Web Fire Mapper (http://maps.geog.umd. edu/maps.asp), which provides hotspots/fires detected by the MODIS Terra and Aqua two times per day. Monthly accumulated hotspots over the Java Island were analyzed over the period of January 2002–March 2004 (Fig. S3, Supplementary information). Largest number of hotspots was found in the middle of the dry season (August–October), indicating more intensive open burning during this period. The SE prevalent wind in the dry season (Fig. 1) would transport the ozone precursors and other pollutants emitted from the main agricultural areas at this upwind southeastern part of Jakarta toward the city. To understand the impact of different emission sources on the ozone air quality in Jakarta a detailed emission inventory for ozone precursors should be first developed. This would facilitate application of photochemical smog modeling to analyze the sensitivity of ozone formation related to the precursor emission reduction for emission control strategy formulation. In addition to the formation of ground level ozone from the precursors there is a possibility of intrusion of ozonerich stratospheric and upper tropospheric air that can

D.A. Permadi, N.T. Kim Oanh / Atmospheric Environment 42 (2008) 6806–6815

JAF 1

February

100

3

2

60

1.5 40

1

20

0.5

0 5

7

9

13

15

NO2 ppb

O3 ppb

17

19

21

1.5 40

1

20

0.5

0

0 11

13

15

NO2 ppb

O3 ppb

17

19

21

100

2 60

1.5

40

1

20

0.5 3

5

7

9

13

15

NO2 ppb

O3 ppb

17

19

21

100

40

1

20

0.5

0

0 13

15

17

19

21

100

1.5 40

1

20

0.5

0 5

7

9

13

15

NO2 ppb

O3 ppb

17

19

21

100

40

1

20

0.5

0

0 O3 ppb

11

NO2 ppb

13

15

17

19

NO ppb

0 3

21

23 CO ppm

5

7

9

11 13 15 17

NO2 ppb

19

21 23 CO ppm

NO ppb

JAF 1

3.5

October

100

3 2.5

80

2 60 1.5 40

1

20

0.5 0 3

5 O3

7

9

11 13 15 17 NO2 NO

19

21 23 CO

3.5

October

100

3 2.5

80

2

60

1.5 40

1

20

0.5 0 3

5

7

9

11 13 15 17 NO2

19

NO

21 23 CO

JAF 5

3.5

October

100

3 2.5

80

2 60 1.5 40

1

20

CO in ppm

1.5

CO in ppm

60

9

0.5

120

3.5

2

7

1

20

O3

3

80

5

1.5 40

1

2.5

3

2

CO ppm

NO ppb

May

1

2.5

60

23

JAF 5

120

Concentration (ppb)

11

Concentration (ppb)

3

3

80

0

0 1

3.5

CO in ppm

60

CO ppm

NO ppb

JAF 4

CO in ppm

2

21 23

120

3 2.5

19

April

1

3.5

80

11 13 15 17

NO2 ppb

100

23

May

9

JAF 5

CO ppm

NO ppb

JAF 4

120

Concentration (ppb)

11

7

0

Concentration (ppb)

9

NO2 ppb

5

CO in ppm

1.5

7

0 3

120

CO in ppm

2.5

60

5

0.5

O3 ppb

3

2

3

1

20

1

3.5

May

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1.5 40

CO ppm

NO ppb

80

1

2 60

23

JAF 1

120

Concentration (ppb)

11

Concentration (ppb)

1

3

0

0

0

3.5

CO in ppm

80

CO ppm

NO ppb

2.5

120

3 2.5

21 23

80

O3 ppb

CO in ppm

Concentration (ppb)

February

NO2 ppb

19

April

1

3.5

120

11 13 15 17

JAF 4

CO ppm

NO ppb

9

100

23

JAF 5

7

0

Concentration (ppb)

9

5

CO in ppm

60

7

0 3

120

CO in ppm

2

5

0.5

O3 ppb

3 2.5

3

1

20

1

3.5

80

1

1.5

40

CO ppm

NO ppb

February

100

2

60

23

JAF 4

120

Concentration (ppb)

11

Concentration (ppb)

3

2.5

80

0

0 1

3

April

100

CO in ppm

2.5

80

JAF 1

120

3.5

CO in ppm

Concentration (ppb)

120

Concentration (ppb)

6810

0.5

0

0 1

3

5 O3

7

9

11 13 15 17 NO2

NO

19

21 23 CO

Fig. 2. Diurnal variation of O3 and precursors during the high O3 (April, May, October) and the low O3 (February) at three monitoring stations in 2002–2003.

D.A. Permadi, N.T. Kim Oanh / Atmospheric Environment 42 (2008) 6806–6815

contribute to diurnal and seasonal O3 variations in the city. An example of vertical ozone profile (EORC/NASDA, 2002) is included in Fig. S2, Supplementary information showing high ozone concentration at the altitude of around 5 km, which suggests possibility of the downward transport of O3 when strong convective motion exists (Ninong and Slamet, 1995). This is an interesting a subject of further study especially for the near equator location of Jakarta. 4.5. Ozone episodes’ analysis

400

a

The diurnal variation of O3 and its precursors during the October episode days (Fig. 4) follows the same patterns as the monthly average (Fig. 2) discussed earlier, with the morning peaks of precursors lower than the evening peaks. On October 11 (a Friday), morning and evening peaks of NO and diurnal and NO2 were the highest among the considered days. High ozone for a long period (11:00–16:00) and high NO2 indicate intensive photochemistry. On 12 October 2003 (a Saturday – holiday) the morning peaks were lower than the previous day, which could be linked to lesser morning traffic. As compared to 11 October 2002, the time period between peaked NO and peaked NO2 was also longer, indicating a longer period for NO to NO2 conversion. The evening peaks of CO on 11–12 October 2002 may be linked to high traffic volume during the weekend as well as other outdoor activities such as cooking at food stalls commonly being practiced in the city. Perhaps this source would contribute precursors for the next day ozone formation during the stagnant air conditions. However, no in-depth study on the effects of outdoor food stalls to air quality has been reported in Jakarta. Similar patterns of the diurnal variations were also observed on 22–23 October 2003 but with lower peaks of the pollutants. May 13–14, 2002 (Tuesday and Wednesday) episode was characterized by a rather different variation pattern of the pollutants than the October episodes with a very high morning CO peak which was higher than the evening peak. On May 13, the NO and CO peaks at JAF4 were the highest of all the presented episode days. High ozone was observed for short time and quite early, i.e. 9:00–11:00. On May 14 at JAF1 the high ozone started at 9:00 with a sharp peak at 13:00 then dropped significantly at 14:00. For most days, presented in Fig. 4, NO was reduced to close to zero (below the detection limit) levels from 8:00–19:00 when NO2 elevated indicating high intensity of photochemistry.

2002

300

11-12 Oct 2002

13-14 May 2002

200 100

Dec

Nov

Oct

Sept

Aug

July

June

May

Apr

Mar

Jan

Feb

0

400

b

23-24 April 2003

22-23 Oct 2003

2003

300 200 100

JAF 1

JAF 4

JAF 5

Dec

Nov

Oct

Sept

Aug

July

June

May

Apr

Mar

Feb

0 Jan

O3 concentration (ppb)

O3 concentration (ppb)

4.5.1. Episode screening Hourly highest O3 concentration for each day during the period of January 2002–December 2003 at three stations (JAF1, JAF4 and JAF5), where more complete data are available, is shown in Fig. 3. It is noted that the exceedance of the NAAQS was observed often during the period with a higher frequency during September–November and some high peaks, mainly at JAF5, observed in April–May. The selected episodes of high O3 for in-depth analysis include: (i) 11–12 October 2002; (ii) 22–23 October 2003; (iii) 23–24 April 2003; and (iv) 13–14 May 2002, when ozone was high at several stations. The highest hourly ozone observed in the city during episodes 1, 2, 3 and 4 were 142–184 ppb, 123–151 ppb, 115–356 and 135– 274 ppb, respectively, which all exceeded the hourly NAAQS (120 ppb). During October episodes’ ozone was high at JAF4 and JAF5 which are the downwind of the city center during the dry season as mentioned above. During the May episode, on 13 May 2002 the hourly high ozone levels of 160 and 135 ppb were also observed at JAF4 and JAF5 while on 14 May 2002 the high ozone was observed only at JAF1 but quite extreme (274 ppb). A single extremely high 1 h-O3 was observed on 24 April 2003 at only JAF5 which was located downwind of the city center the time.

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NAAQS

Fig. 3. Time series of daily highest 1 h-O3 during (a) January–December 2002 and (b) January–December 2003 at different stations in Jakarta.

D.A. Permadi, N.T. Kim Oanh / Atmospheric Environment 42 (2008) 6806–6815

200

0

5

7

9

11 13 15 17 19 21 23

400

200

0

1

3

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0

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NO2

O3

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17

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21

8 7 6 5 4 3 2 1 0

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400

1

8 7 6 5 4 3 2 1 0

23

200

3

8 7 6 5 4 3 2 1 0

23

200

3

8 7 6 5 4 3 2 1 0

23

14 May 2002 (JAF 4)

11 13 15 17 19 21 23 NO

21

400

1 0

0

19

0

CO in ppm

200

17

13 May 2002 (JAF 5)

1 8 7 6 5 4 3 2

23 April 2003 (JAF 5) C in ppb

1

11 13 15 17 19 21 23

400

11 13 15

400

CO in ppm

C in ppb

14 May 2002 (JAF 1)

9

0

1 8 7 6 5 4 3 2 1 0

7

200

11 13 15 17 19 21 23

400

5

23 Oct 2003 (JAF 4)

CO in ppm

C in ppb

13 May 2002 (JAF 4)

8 7 6 5 4 3 2 1 0

3

400

CO in ppm

C in ppb

22 Oct 2003 (JAF 4)

3

1 8 7 6 5 4 3 2 1 0

C in ppb

C in ppb

400

1

0

11 13 15 17 19 21 23

C in ppb

9

C in ppb

7

C in ppb

5

CO in ppm

3

CO in ppm

1

200

8 7 6 5 4 3 2 1 0

CO in ppm

0

12 Oct 2002 (JAF 5)

CO in ppm

200

400

CO in ppm

11 Oct 2002 (JAF 4)

CO in ppm

8 7 6 5 4 3 2 1 0

400

C in ppb

6812

23

CO

Fig. 4. Diurnal variation of ambient levels of NO, NO2, O3 and CO on episode days.

The April 23–24, 2003 (Wednesday and Thursday) episode was also characterized by higher value of CO evening peak than morning peak similar to the October episodes. On 23 April the ozone peak was observed earlier, i.e. 10:00–11:00 and high ozone levels remained until late afternoon (17:00), while NO was reduced to the level of 14 ppb during the time. On April 24 very high O3 levels were observed starting from 14:00 (230 ppb) and peaks on 16:00 p.m. (356 ppb) which

were quite late compared with the other episodes and with the average pattern (Fig. 2). It is noted that NO was reduced to low values at around midday, 14 ppb on 23 April and 3 ppb on 24 April, but was not as low as the previously discussed episodes. The daily pattern of CO on 24 April (Wednesday) was also unusual which may be due to a change in emission pattern (additional sources or change in traffic pattern) or stagnant air that circulated the emission in the city.

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Possible influence of biomass burning to the high ozone in the episode days was examined using the daily hotspots counts (MODIS, two times per day) for Java islands (agriculture and forestry areas). The highest number of hotspots (23) was recorded on 11 October 2002 while a few were observed during other days (Table 2). The 24-h back trajectory of the air masses arriving at Jakarta on the selected days was analyzed using HYSPLIT4 (http://www.arl.noaa.gov/ready.html) show that the air masses passed through the locations with more dense hotspots (Fig. S4, Supplementary information) during the October and April episodes. The precursors emitted from biomass burning thus may contribute to elevated ozone levels in Jakarta in October when the city was located about 50–100 km downwind of the intensive burning areas. On the May episode, only a single hotspot was detected each day and the air mass had also the origin on the Java Island but travelling over shorter distance which indicates regional stagnant air conditions and the trajectory did not pass the hotspot. It is also noted that the horizontal motion of the air masses on the episode days was E–SE. On the low ozone day of February, the air mass origin was to the NW of the city, i.e. opposite to the May, April and October. 4.5.2. Typical meteorological conditions during O3 episodes Surface meteorological conditions during the selected episode days were compared with the respective monthly mean values during monitoring period 2002–2003, as well as the values on selected low O3 days in February (Table 2). The average wind speeds on the presented days were lower than the monthly average values (in parentheses). On the episode days, the daily average relative humidity (RH) was lower than the monthly means, while maximum hourly global radiation (GR) and temperature were higher. In contrast, during the low ozone days in February the RH were higher than the February monthly mean and some light rain was also observed (Table 2). Note that the maximum hourly GR was fluctuating with the highest value on October 11, 2002 (812 W m2) as compared to the monthly average of 329 W m2. These GR values are, however, generally lower than those reported in Zhang (2002) for Bangkok where the maximum hourly GR during the episode days could reach above

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900 W m2. On April 24 the average wind was very low as compared to the monthly average indicating the stagnant air in the city which may explain the extremely high maximum ozone recorded. Prevalent local wind direction during the midday (10:00–16:00), when ozone was high, was NE in all episodes though the large-scale wind indicated by the back trajectory of air masses mentioned earlier show the SE direction for all presented episode days. Only in February the local and the large-scale wind directions were consistent. This observation agrees with that by Sofyan et al. (2007) who noted that the lower atmosphere of Jakarta is not largely affected by synoptic scale wind. In fact, it may be a reflection of the city topography which is bounded by a mountain range extending along the south coast of the West Java Island with the average height of 1500 m. The highest elevations are along the south most border with Salak, a mountain range with the summit of 3019 m, located to the SE of the city. This mountain range has an almost V-shape which is directed along NE on one side and NW on the other. It, therefore, blocks the SE wind and modifies it to follow the NE direction but would not alter the NW wind. Hence, for NW wind the local and large-scale wind directions coincide. It was observed also that the diurnal wind direction varied substantially following the sea–land breeze. During the daytime the sea breeze would strengthen the northerly wind. As a way of example, on 12 October 2002 the N–NE wind was dominant in the daytime while the southerly (S) wind was dominant in the nighttime. The streamline charts (NOAA, 2007) and synoptic charts over the west Java Island on selected episode days and on the February days with low O3 were analyzed. Examples of these charts at 06:00 UTC or 13:00 LST are presented in Fig. S5 (Supplementary information). Note that on episode days in October the synoptic scale flows were consistently SE with no significant diurnal changes, which show the typical of SE monsoon circulation. During the ozone episode of 13–14 May 2002, the E–SE synoptic flow was observed over the study area. On contrary, in February, i.e. in the rainy season, the NW synoptic flows (NW monsoon) dominate. These synoptic flows have been captured well in the back trajectory analysis presented earlier.

Table 2 Meteorological data for episodic high and low O3 days Episode days

Max O3a (ppb)

WSa (m s1)

WDa (deg)

RHa (%)

GRa (W m2)

T a ( C)

Visibilityb (km)

RIb (mm)

No of hotspotsc

11 Oct 2002 12 Oct 2002 22 Oct 2003 23 Oct 2003 13 May 2002 14 May 2002 24 April 2003 20 Feb 2002 21 Feb 2003

172 184 151 124 160 274 356 24 28

1.3(1.4) 1.3(1.4) 1.3(1.4) 1.1(1.4) 1.3(1.9) 1.0(1.9) 0.89(1.6) 1.6(2.1) 1.6(2.1)

NE NE NE NE NE NE NE NW NW

71(72) 67(72) 69(72) 69(72) 72(76) 71(76) 74(74.5) 88(84) 97(84)

812(329) 795(329) 735(329) 762(329) 739(271) 715(271) 612(149) 603(240) 204(240)

34.8(28.6) 34.5(28.6) 35.3(28.6) 36.1(28.6) 34.1(28.3) 34.2(28.3) 32.5(28.5) 30.6(26.7) 26.4(26.7)

10 8 5 5 10 10 10 10 6

0 0 0 0 0 0 0 20 25

23 2 4 9 1 1 4 3 4

WS: Wind speed (daily average), WD: Wind direction (prevalent at 10–16:00), RH: Relative humidity (daily average), GR: Global radiation (highest hourly in the day), T: Temperature (daily maximum), RI: Rainfall intensity (at 13:00 LST). Values in parentheses are the monthly average during 2002–2003. a Data are reported for monitoring station which had the highest O3 in the city. b Data from http://envf.ust.hk/dataview/gts published by Institute for the Environment (IENV), the Hong Kong University of Science and Technology (HKUST). c Number of hotspots counting in Java island, source: http://maps.geog.umd.edu/web fire mapper/south East Asia.

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On the October episode days, the northern hemisphere synoptic situations were generally characterized by a presence of the Intertropical Convergence Zone (ITCZ) over the Continental Southeast Asia (across southern Thailand) and a high pressure system over China (Fig. S5, Supplementary information). On the southern hemisphere, there was a high pressure cell developed over the Australian continent which influences the study area and brings about the SE monsoon circulation over Jakarta. On the 13–14 May 2002 episode, tropical cyclone was observed over the Indian Ocean to the SW of Jakarta. On April 24, 2003 the whole Southeast Asia region was dominated by low pressure cells extending from a vast heat low pressure over India. Late April and early May are in fact the transitional monsoon period between the rainy and dry seasons. During all discussed episodes, a weak pressure gradient over the Java Island, especially during April episode, was observed. This would result in the low wind condition leading to the stagnant air that favors the build-up of air pollution including ozone in the city. On the days with low O3 in February the study area was influenced by a strong low pressure system, centered over Australia, and a strong pressure gradient over Jakarta was observed. On the Northeast Asia, a strong high pressure system was present over China with a ridge reach deep into the Continental Southeast Asia. This synoptic situation result in a stronger wind over Jakarta, i.e. on 20 February 2002, at 06:00 UTC, the NW wind with a speed above 4 m s1 was observed. It is commonly observed that ozone episodes normally occur when the study area is under a weak pressure gradient field that would lead to low wind conditions and enhance the accumulation and build-up all pollutants over the city including ozone precursors and ozone. 5. Conclusions Analysis of surface O3 monitoring data in Jakarta showed that ozone diurnal and seasonal variations are consistent with the meteorological conditions and precursor emission patterns. The results are comparable with published patterns of O3 at other urban areas in Asia though the average daily peak of ozone in Jakarta appears somewhat earlier, at around 12:00, corresponding to the daily peak in global radiation in the city. High O3 levels in Jakarta during the dry season are strongly linked to both more favorable meteorology and possibly more intensive precursor emissions. Traffic is the largest source of precursors’ emission year around which has resulted in almost the same ambient concentrations of precursors during both high ozone months (April, May and October) and low ozone months (February). The contribution from open burning of the agricultural wastes in the island may be significant especially during the dry season (October) when the burning is intensive and the city is located downwind of the agricultural area. A weak pressure gradient is commonly observed over the city on high ozone days that limits horizontal air motion and enhances the build-up of ozone and its precursors. The presence of a high pressure over Australia and Indonesia is normally observed during the high ozone days while the influence of a low pressure

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