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Impacts of biomass burning and regional haze on the pH of rainwater in Brunei Darussalam
Atmospheric Environment 34 (2000) 2739}2744
Impacts of biomass burning and regional haze on the pH of rainwater in Brunei Darussalam M. Radojevic *, K.S. Tan Department of Chemistry, University of Brunei Darussalam, Bandar Seri Begawan BE1410, Brunei Darussalam Department of Physics, University of Brunei Darussalam, Bandar Seri Begawan BE1410, Brunei Darussalam Received 5 February 1999; received in revised form 17 July 1999; accepted 26 July 1999
Abstract A number of reports have suggested that biomass burning in the tropics may have an acidifying e!ect on precipitation with consequent e!ects on tropical ecosystems. Although SE Asia has been repeatedly a!ected by severe haze caused by tropical forest "res, the impacts on rainwater acidity and chemistry have not yet been reported. In the present communiction we report, for the "rst time, the impacts of "res and haze on rainwater pH in SE Asia during the past three haze episodes. The analysis of rainwater in Brunei Darussalam during severe haze episodes in Borneo in 1994, 1997, and 1998 failed to reveal any signi"cant impacts on rainwater acidity or wet deposition of hydrogen ions. 2000 Elsevier Science Ltd. All rights reserved. Keywords: Acid rain; Haze; Biomass burning; Wet deposition; Rainwater
1. Introduction Over the last 10 yr a number of authors have suggested that forest "res in the tropics may have an acidifying e!ect on rainwater with potential consequences for tropical ecosystems (Crutzen and Andreae, 1990; Lacaux et al., 1991}1993; Cachier and Ducret, 1991). While there have been few studies on the impacts of biomass burning on rainwater chemistry in South America and Africa, no such studies have been reported in SE Asia, a region that has been severely a!ected by haze from forest "res in recent years (Radojevic, 1998). Biomass "res are inversely related to precipitation; they generally occur during dry periods when precipitation amounts are very low or non-existent since heavy rains tend to put the "res out. Therefore, one would anticipate that even if the acidity and the ionic content of individual rainwater samples, that is when there is any rain, may be high, the wet deposition rates would tend to be low simply because
* Corresponding author. Fax: #673-2-249502. E-mail address: [email protected] (M. Radojevic).
rainfall amounts are so low during the burning season. Most wet deposition takes place during the wet season when precipitation amounts are exceedingly large. It is the deposition rates that should be related to ecological impacts, rather than the composition of individual rainwater samples as has been done in some reported studies (Lacaux et al., 1991}1993).
2. Materials and methods We have previously noted the occurrence of acidic precipitation in Borneo similar to that observed in other tropical regions (Radojevic and Lim, 1995). Extensive forest "res in Borneo and Sumatra have been responsible for major regional haze episodes in SE Asia, notably in 1994, 1997, and 1998 (Radojevic, 1997,1998). Although intense "res burn during dry periods when rainfall amounts are unusually low, precipitation samples were collected and analysed during the 1994, 1997, and 1998 episodes. Experimental details of rainwater analysis have been published previously (Radojevic and Lim, 1995). Samples were analysed for pH immediately after collection. Bulk samplers were used to collect precipitation
1352-2310/00/$ - see front matter 2000 Elsevier Science Ltd. All rights reserved. PII: S 1 3 5 2 - 2 3 1 0 ( 9 9 ) 0 0 3 3 9 - 8
2740
M. Radojevic, K.S. Tan / Atmospheric Environment 34 (2000) 2739}2744
during the 1994 haze episode. Wet-only samples were collected during the 1997 and 1998 haze episodes using an automated wet-only collector, with the exception of samples collected in Bandar Seri Begawan on 21 February 1998 and in Seria during April 1998, which were bulk samples collected on a daily basis.
3. Results and discussion The main forest "re hot-spots and the area a!ected by regional haze during the last three major episodes in SE
Asia are indicated in Fig. 1. In Indonesia, the 1994 "res consumed an area greater than 50,000 km (Nichol, 1997). The 1994 regional haze episode a!ected Brunei between the middle of August and the beginning of October due to the long-range transport of pollution from the Kalimantan region of Borneo and from Sumatra. The prevailing wind direction was generally southerly and southwesterly, characteristic of that time of the year. It should be noted that the 1994 episode was considerably less severe in Brunei than the 1997 or 1998 episodes. The forested area scorched by "res in Indonesia during the 1997 episode is estimated at around 21,000 km (Simons,
Fig. 1. Approximate location of forest "re hot-spots and area a!ected by regional haze in SE Asia. (000) August}October 1994, (} } }) July}October 1997, ( ) February}April 1998. (䉱) Site of forest "res.
M. Radojevic, K.S. Tan / Atmospheric Environment 34 (2000) 2739}2744
2741
Table 1 Occurrence of haze from forest "res, and rainfall in Brunei Darussalam during the 1994 regional haze episode. <"visual range
No. of haze days Dates when <)5000 m Duration of haze (h) Dates when <)2000 m Duration of haze (h) Dates of rain#haze Sampling dates
August
September
October
2 10, 23 7 * 0 * 10}13, 23}27
22 3}9, 14}15, 18}30 301 6, 22}24, 30 29 6}7, 9, 18}20, 23}24, 26}28, 30 3}7, 7}13, 14}26, 26}28, 28}1/10
3 1}3 59 1}2 31 * 1}4
1998), however, there were signi"cant local "res in the northern Borneo states of Brunei, Sarawak and Sabah. In Brunei, "res consumed about 40 km of forested land during 1997 and 1998. The haze in Brunei during the 1998 episode was largely due to local "res. Dates when haze was present in Brunei during 1994 are summarised in Table 1 on the basis of two visibility categories, )5000 m and )2000 m. We either sampled rainfall when it coincided with haze occurrence, or we sampled the "rst rain that fell after a haze event. The 1997 haze episode ocurred between August and mid-October and it was also caused by the long-range transport of pollutants from forest "res in Indonesia. Southwesterly and southeasterly winds dominated over SE Asia during most of the 1997 episode (Tick and Hai, 1999). In September 1997, southeasterly winds in the southern hemisphere were particularly strong and these advected smoke particles from forest "res in Sumatra and Kalimantan towards Peninsular Malaysia and northern Borneo, leading to the most severe haze conditions. By November 1997, easterlies cleared the haze from most of Malaysia. During the period July}October 1997, southern Peninsular Malaysia and northern Borneo experienced below normal rainfall. The haze of 1997 was considerably more severe than that of 1994 with visibility decreasing to 200}700 m throughout Brunei for up to a week at a time. No aerosol measurements were available in Brunei during the 1997 episode, but in neighbouring Sarawak, the PM concentration climbed to almost 1 mg m\ during the worst period of the haze. The haze was washed out by heavy rainfall early in October and it disappeared completely by 10 October 1997. We have pH measurements for all the rainfall during this period but no other data on the chemical composition of the rain. The 1998 haze episode di!ered signi"cantly in origin, severity, and prevailing wind direction from the 1994 and 1997 episodes. Severe haze a!ected Brunei from February to the end of April 1998 with visibility often dropping to below 2000 m and at times to 100 m. Most of the haze was due to local "res in Brunei and the northern Borneo states of Sarawak and Sabah, with the most intense "res burning in the border region between Brunei
and Sarawak. Long-range transport of pollutants from Kalimantan, where forest "res were also burning, had little impact on northern Borneo due to the prevailing wind direction at the time, which was mainly northerly and northeasterly. This is in sharp contrast to the 1994 and 1997 haze episodes in Brunei, Sarawak and Sabah, which were largely caused by forest "res in Indonesia. The months of February, March and April have the lowest average monthly rainfall and this coincides with the vernal equinoctial season (Sirinanda, 1990). Eastern Sarawak, Sabah, Brunei and eastern Kalimantan received below average rainfall during the months of February, March and April 1998 (Tick and Hai, 1999). The months of February and March were unusually dry in Brunei during 1998; only one sample was collected on 21 February 1998 while no rain fell during extremely severe forest "re and haze events in March 1998 when PM concentrations climbed to almost 1 mg m\ on several occasions. Rainwater samples were also collected in the town of Seria, closer to the area of major "res on several days in April 1998. The pH values of all the rainwater sampled in Brunei during the haze episodes of 1994, 1997, and 1998 are given in Fig. 2. The volume weighted mean pH of rainfall determined from 228 rainwater samples collected during periods una!ected by biomass "res and haze is shown as a line for comparison. The data does not demonstrate any signi"cant acidifying e!ect of biomass burning on rainwater, contrary to what has been postulated in the literature (Crutzen and Andreae, 1990; Lacaux et al., 1991}1993; Cachier and Ducret, 1991). Although biomass burning produces many acidifying compounds, for example SO , NO , and organic acids such as formic and acetic acid, it also produces ions such as Ca>, Mg> and K>, which may act to neutralise the acidity (Ward and Hardy, 1991). We have a complete annual data set of pH measurements from July 1995 to 1996 when there was no signi"cant biomass burning or haze in Borneo. The total annual wet deposition of H> was 0.046 eq m\. Taking this value as a reference, the contribution of H> deposition during periods of biomass burning to the annual wet deposition of H> was calculated (Table 2). The
Fig. 2. pH of rainwater samples collected in Brunei Darussalam during episodes of biomass "res and haze in 1994, 1997, and 1998. Line is VWM pH of 228 rainwater samples collected in absence of biomass "res and haze.
2742 M. Radojevic, K.S. Tan / Atmospheric Environment 34 (2000) 2739}2744
M. Radojevic, K.S. Tan / Atmospheric Environment 34 (2000) 2739}2744
2743
Table 2 Wet deposition of H> in Brunei Darussalam during episodes of forest "res and haze and percentage of contribution to total annual wet deposition of H> Haze period
No. of samples
Rainfall amount (mm)
VWM pH
Deposition of H>(leq m\)
Percentage of total annual deposition of H>
5.02 4.63 4.88
334 2460 58
0.73 5.35 0.13
2852
6.21
459 1830 853
1.00 3.98 1.85
3142
6.83
95 0 141
0.21 0.00 0.31
236
0.52
August 1994 September 1994 October 1994
2 5 1
35.3 104.3 4.4
Total 1994 episode
8
144.0
August 1997 September 1997 October 1997
8 9 5
64.0 273.3 189.9
22
527.2
February 1998 March 1998 April 1998
1 0 8
18.2 0.0 115.2
Total 1998 episode
9
133.4
Total 1997 episode
5.14 5.17 5.35
5.28 * 5.91
Note: Complete monthly data sets except for August 1994, October 1994, and October 1997 for which only periods a!ected by haze are included. All deposition values were calculated as sum of products of H> concentration and rainfall amount of individual rainwater samples. Mean of 5 samples collected at di!erent sites on same date. Reference annual H> deposition taken as 0.046 eq m\ determined during a 1 yr period (1995}1996) in absence of forest "res and haze.
monthly contributions during episodes of biomass "res and haze to the total annual wet deposition varied between 0.0 and 5.35%. Even assuming that all of the H> during haze episodes was due to biomass "res (which it obviously is not) the results suggest that forest "res are a minor source of acidity in wet deposition. Our rainwater results agree with studies of rainwater composition in Venezuela during periods of biomass "res. In these studies higher concentrations of all ions were observed than during periods when there were no biomass "res. Higher pH values were observed during periods of vegetation burning in one study (Sanhueza et al., 1989) while in the other it was concluded that biomass burning had no signi"cant e!ect on rainwater acidity (Sanhueza et al., 1992). Although Lacaux et al. (1987) also observed higher pH values during the dry season than during the rainy season in the Ivory Coast, in later studies they claimed a signi"cant contribution of biomass burning, during the dry season to rainwater acidity (Lacaux et al, 1993).
Acknowledgements We would like to thank the Meteorological Service, Department of Civil Aviation, Ministry of Communi-
cations, Government of Brunei and Dr. T.R. Muraleedharan of Brunei Shell Petroleum Co. Sdn Bhd for supplying some of the information used in this report. Thanks are also due to L.H. Lim, R. Medan and M. Kasim for performing some of the analyses. References Cachier, H., Ducret, J., 1991. In#uence of biomass burning on equatorial rains. Nature 352, 228}230. Crutzen, P.J., Andreae, M.O., 1990. Biomass burning in the tropics: impacts on atmospheric chemistry and biogeochemical cycles. Science 250, 1669}1678. Lacaux, J.-P., Cachier, H., Delmas, R., 1993. Biomass burning in Africa: an overview of its impacts on atmospheric chemistry. In: Crutzen, J.P., Goldammer, J.G. (Eds.), Fire in the Environment: The Ecological, Atmospheric, and Climatic Importance of Vegetation Fires. Wiley, Chichester, pp. 159}191. Lacaux, J.-P., Delmas, R.A., Cros, B., Lefeivre, B., Andreae, M.O., 1991. In#uence of biomass burning emissions on precipitation chemistry in the equatorial forests of Africa. In: Levine, J.S. (Ed.), Global Biomass Burning. Cambridge, MA, MIT Press, pp. 167}174. Lacaux, J.P., Loemba-Ndembi, J., Lefeivre, B., Cros, B., Delmas, R., 1992. Biogenic emissions and biomass burning in#uences on the chemistry of the fogwater and stratiform precipita-
2744
M. Radojevic, K.S. Tan / Atmospheric Environment 34 (2000) 2739}2744
tions in the African equatorial forest. Atmospheric Environment 26A, 541}551. Lacaux, J.-P., Servant, J., Baudet, J.G.R., 1987. Acid rain in the tropical forests of western Africa. In: Perry, R., Harrison, R.M., Bell, J.N.B., Lester, J.N. (Eds.), Acid Rain } Scienti"c and Technical Advances. Selper Ltd, London, pp. 264}269. Nichol, J., 1997. Bioclimatic impacts of the 1994 smoke haze event in Southeast Asia. Atmospheric Environment 31, 1209}1219. Radojevic, M., 1997. The haze in South East Asia. Environmental Scientist 6, 1}3. Radojevic, M., 1998. Burning issues. Chemistry in Britain 34 (12), 38}42. Radojevic, M., Lim, L.H., 1995. A rain acidity study in Brunei Darussalam. Water, Air and Soil Pollution 85, 2369}2374.
Sanhueza, E., Arias, M.C., Donoso, L., Graterol, N., Hermoso, M., Marti, I., Romero, J., Rondon, A., Santana, M., 1992. Chemical composition of acid rains in the Venezuelan savannah region. Tellus 44B, 54}62. Sanhueza, E., Elbert, W., Rondon, A., Arias, M.C., Hermoso, M., 1989. Organic and inorganic acids in rain from a remote site of the Venezuelan savannah. Tellus 41B, 170}176. Simons, L.M., 1998. Indonesia's plague of "re. National Geographic 194 (2), 100}118. Sirinanda, K.U., 1990. Rainfall seasonality in Negara Brunei Darussalam. Asian Geographer 9, 39}52. Tick, L.J., Hai, O.S., 1999. E!ects of biomass burning in Malaysia}Indonesia region during the 1997}1998 El Nino. Paper presented at the International Workshop on Biomass Burning and its Transport, 1}3 March 1999, Kuala Lumpur. Ward, D.E., Hardy, C.C., 1991. Smoke emissions from wildland "res. Environment International 17, 117}134.
Impacts of biomass burning and regional haze on the pH of rainwater in Brunei Darussalam M. Radojevic *, K.S. Tan Department of Chemistry, University of Brunei Darussalam, Bandar Seri Begawan BE1410, Brunei Darussalam Department of Physics, University of Brunei Darussalam, Bandar Seri Begawan BE1410, Brunei Darussalam Received 5 February 1999; received in revised form 17 July 1999; accepted 26 July 1999
Abstract A number of reports have suggested that biomass burning in the tropics may have an acidifying e!ect on precipitation with consequent e!ects on tropical ecosystems. Although SE Asia has been repeatedly a!ected by severe haze caused by tropical forest "res, the impacts on rainwater acidity and chemistry have not yet been reported. In the present communiction we report, for the "rst time, the impacts of "res and haze on rainwater pH in SE Asia during the past three haze episodes. The analysis of rainwater in Brunei Darussalam during severe haze episodes in Borneo in 1994, 1997, and 1998 failed to reveal any signi"cant impacts on rainwater acidity or wet deposition of hydrogen ions. 2000 Elsevier Science Ltd. All rights reserved. Keywords: Acid rain; Haze; Biomass burning; Wet deposition; Rainwater
1. Introduction Over the last 10 yr a number of authors have suggested that forest "res in the tropics may have an acidifying e!ect on rainwater with potential consequences for tropical ecosystems (Crutzen and Andreae, 1990; Lacaux et al., 1991}1993; Cachier and Ducret, 1991). While there have been few studies on the impacts of biomass burning on rainwater chemistry in South America and Africa, no such studies have been reported in SE Asia, a region that has been severely a!ected by haze from forest "res in recent years (Radojevic, 1998). Biomass "res are inversely related to precipitation; they generally occur during dry periods when precipitation amounts are very low or non-existent since heavy rains tend to put the "res out. Therefore, one would anticipate that even if the acidity and the ionic content of individual rainwater samples, that is when there is any rain, may be high, the wet deposition rates would tend to be low simply because
* Corresponding author. Fax: #673-2-249502. E-mail address: [email protected] (M. Radojevic).
rainfall amounts are so low during the burning season. Most wet deposition takes place during the wet season when precipitation amounts are exceedingly large. It is the deposition rates that should be related to ecological impacts, rather than the composition of individual rainwater samples as has been done in some reported studies (Lacaux et al., 1991}1993).
2. Materials and methods We have previously noted the occurrence of acidic precipitation in Borneo similar to that observed in other tropical regions (Radojevic and Lim, 1995). Extensive forest "res in Borneo and Sumatra have been responsible for major regional haze episodes in SE Asia, notably in 1994, 1997, and 1998 (Radojevic, 1997,1998). Although intense "res burn during dry periods when rainfall amounts are unusually low, precipitation samples were collected and analysed during the 1994, 1997, and 1998 episodes. Experimental details of rainwater analysis have been published previously (Radojevic and Lim, 1995). Samples were analysed for pH immediately after collection. Bulk samplers were used to collect precipitation
1352-2310/00/$ - see front matter 2000 Elsevier Science Ltd. All rights reserved. PII: S 1 3 5 2 - 2 3 1 0 ( 9 9 ) 0 0 3 3 9 - 8
2740
M. Radojevic, K.S. Tan / Atmospheric Environment 34 (2000) 2739}2744
during the 1994 haze episode. Wet-only samples were collected during the 1997 and 1998 haze episodes using an automated wet-only collector, with the exception of samples collected in Bandar Seri Begawan on 21 February 1998 and in Seria during April 1998, which were bulk samples collected on a daily basis.
3. Results and discussion The main forest "re hot-spots and the area a!ected by regional haze during the last three major episodes in SE
Asia are indicated in Fig. 1. In Indonesia, the 1994 "res consumed an area greater than 50,000 km (Nichol, 1997). The 1994 regional haze episode a!ected Brunei between the middle of August and the beginning of October due to the long-range transport of pollution from the Kalimantan region of Borneo and from Sumatra. The prevailing wind direction was generally southerly and southwesterly, characteristic of that time of the year. It should be noted that the 1994 episode was considerably less severe in Brunei than the 1997 or 1998 episodes. The forested area scorched by "res in Indonesia during the 1997 episode is estimated at around 21,000 km (Simons,
Fig. 1. Approximate location of forest "re hot-spots and area a!ected by regional haze in SE Asia. (000) August}October 1994, (} } }) July}October 1997, ( ) February}April 1998. (䉱) Site of forest "res.
M. Radojevic, K.S. Tan / Atmospheric Environment 34 (2000) 2739}2744
2741
Table 1 Occurrence of haze from forest "res, and rainfall in Brunei Darussalam during the 1994 regional haze episode. <"visual range
No. of haze days Dates when <)5000 m Duration of haze (h) Dates when <)2000 m Duration of haze (h) Dates of rain#haze Sampling dates
August
September
October
2 10, 23 7 * 0 * 10}13, 23}27
22 3}9, 14}15, 18}30 301 6, 22}24, 30 29 6}7, 9, 18}20, 23}24, 26}28, 30 3}7, 7}13, 14}26, 26}28, 28}1/10
3 1}3 59 1}2 31 * 1}4
1998), however, there were signi"cant local "res in the northern Borneo states of Brunei, Sarawak and Sabah. In Brunei, "res consumed about 40 km of forested land during 1997 and 1998. The haze in Brunei during the 1998 episode was largely due to local "res. Dates when haze was present in Brunei during 1994 are summarised in Table 1 on the basis of two visibility categories, )5000 m and )2000 m. We either sampled rainfall when it coincided with haze occurrence, or we sampled the "rst rain that fell after a haze event. The 1997 haze episode ocurred between August and mid-October and it was also caused by the long-range transport of pollutants from forest "res in Indonesia. Southwesterly and southeasterly winds dominated over SE Asia during most of the 1997 episode (Tick and Hai, 1999). In September 1997, southeasterly winds in the southern hemisphere were particularly strong and these advected smoke particles from forest "res in Sumatra and Kalimantan towards Peninsular Malaysia and northern Borneo, leading to the most severe haze conditions. By November 1997, easterlies cleared the haze from most of Malaysia. During the period July}October 1997, southern Peninsular Malaysia and northern Borneo experienced below normal rainfall. The haze of 1997 was considerably more severe than that of 1994 with visibility decreasing to 200}700 m throughout Brunei for up to a week at a time. No aerosol measurements were available in Brunei during the 1997 episode, but in neighbouring Sarawak, the PM concentration climbed to almost 1 mg m\ during the worst period of the haze. The haze was washed out by heavy rainfall early in October and it disappeared completely by 10 October 1997. We have pH measurements for all the rainfall during this period but no other data on the chemical composition of the rain. The 1998 haze episode di!ered signi"cantly in origin, severity, and prevailing wind direction from the 1994 and 1997 episodes. Severe haze a!ected Brunei from February to the end of April 1998 with visibility often dropping to below 2000 m and at times to 100 m. Most of the haze was due to local "res in Brunei and the northern Borneo states of Sarawak and Sabah, with the most intense "res burning in the border region between Brunei
and Sarawak. Long-range transport of pollutants from Kalimantan, where forest "res were also burning, had little impact on northern Borneo due to the prevailing wind direction at the time, which was mainly northerly and northeasterly. This is in sharp contrast to the 1994 and 1997 haze episodes in Brunei, Sarawak and Sabah, which were largely caused by forest "res in Indonesia. The months of February, March and April have the lowest average monthly rainfall and this coincides with the vernal equinoctial season (Sirinanda, 1990). Eastern Sarawak, Sabah, Brunei and eastern Kalimantan received below average rainfall during the months of February, March and April 1998 (Tick and Hai, 1999). The months of February and March were unusually dry in Brunei during 1998; only one sample was collected on 21 February 1998 while no rain fell during extremely severe forest "re and haze events in March 1998 when PM concentrations climbed to almost 1 mg m\ on several occasions. Rainwater samples were also collected in the town of Seria, closer to the area of major "res on several days in April 1998. The pH values of all the rainwater sampled in Brunei during the haze episodes of 1994, 1997, and 1998 are given in Fig. 2. The volume weighted mean pH of rainfall determined from 228 rainwater samples collected during periods una!ected by biomass "res and haze is shown as a line for comparison. The data does not demonstrate any signi"cant acidifying e!ect of biomass burning on rainwater, contrary to what has been postulated in the literature (Crutzen and Andreae, 1990; Lacaux et al., 1991}1993; Cachier and Ducret, 1991). Although biomass burning produces many acidifying compounds, for example SO , NO , and organic acids such as formic and acetic acid, it also produces ions such as Ca>, Mg> and K>, which may act to neutralise the acidity (Ward and Hardy, 1991). We have a complete annual data set of pH measurements from July 1995 to 1996 when there was no signi"cant biomass burning or haze in Borneo. The total annual wet deposition of H> was 0.046 eq m\. Taking this value as a reference, the contribution of H> deposition during periods of biomass burning to the annual wet deposition of H> was calculated (Table 2). The
Fig. 2. pH of rainwater samples collected in Brunei Darussalam during episodes of biomass "res and haze in 1994, 1997, and 1998. Line is VWM pH of 228 rainwater samples collected in absence of biomass "res and haze.
2742 M. Radojevic, K.S. Tan / Atmospheric Environment 34 (2000) 2739}2744
M. Radojevic, K.S. Tan / Atmospheric Environment 34 (2000) 2739}2744
2743
Table 2 Wet deposition of H> in Brunei Darussalam during episodes of forest "res and haze and percentage of contribution to total annual wet deposition of H> Haze period
No. of samples
Rainfall amount (mm)
VWM pH
Deposition of H>(leq m\)
Percentage of total annual deposition of H>
5.02 4.63 4.88
334 2460 58
0.73 5.35 0.13
2852
6.21
459 1830 853
1.00 3.98 1.85
3142
6.83
95 0 141
0.21 0.00 0.31
236
0.52
August 1994 September 1994 October 1994
2 5 1
35.3 104.3 4.4
Total 1994 episode
8
144.0
August 1997 September 1997 October 1997
8 9 5
64.0 273.3 189.9
22
527.2
February 1998 March 1998 April 1998
1 0 8
18.2 0.0 115.2
Total 1998 episode
9
133.4
Total 1997 episode
5.14 5.17 5.35
5.28 * 5.91
Note: Complete monthly data sets except for August 1994, October 1994, and October 1997 for which only periods a!ected by haze are included. All deposition values were calculated as sum of products of H> concentration and rainfall amount of individual rainwater samples. Mean of 5 samples collected at di!erent sites on same date. Reference annual H> deposition taken as 0.046 eq m\ determined during a 1 yr period (1995}1996) in absence of forest "res and haze.
monthly contributions during episodes of biomass "res and haze to the total annual wet deposition varied between 0.0 and 5.35%. Even assuming that all of the H> during haze episodes was due to biomass "res (which it obviously is not) the results suggest that forest "res are a minor source of acidity in wet deposition. Our rainwater results agree with studies of rainwater composition in Venezuela during periods of biomass "res. In these studies higher concentrations of all ions were observed than during periods when there were no biomass "res. Higher pH values were observed during periods of vegetation burning in one study (Sanhueza et al., 1989) while in the other it was concluded that biomass burning had no signi"cant e!ect on rainwater acidity (Sanhueza et al., 1992). Although Lacaux et al. (1987) also observed higher pH values during the dry season than during the rainy season in the Ivory Coast, in later studies they claimed a signi"cant contribution of biomass burning, during the dry season to rainwater acidity (Lacaux et al, 1993).
Acknowledgements We would like to thank the Meteorological Service, Department of Civil Aviation, Ministry of Communi-
cations, Government of Brunei and Dr. T.R. Muraleedharan of Brunei Shell Petroleum Co. Sdn Bhd for supplying some of the information used in this report. Thanks are also due to L.H. Lim, R. Medan and M. Kasim for performing some of the analyses. References Cachier, H., Ducret, J., 1991. In#uence of biomass burning on equatorial rains. Nature 352, 228}230. Crutzen, P.J., Andreae, M.O., 1990. Biomass burning in the tropics: impacts on atmospheric chemistry and biogeochemical cycles. Science 250, 1669}1678. Lacaux, J.-P., Cachier, H., Delmas, R., 1993. Biomass burning in Africa: an overview of its impacts on atmospheric chemistry. In: Crutzen, J.P., Goldammer, J.G. (Eds.), Fire in the Environment: The Ecological, Atmospheric, and Climatic Importance of Vegetation Fires. Wiley, Chichester, pp. 159}191. Lacaux, J.-P., Delmas, R.A., Cros, B., Lefeivre, B., Andreae, M.O., 1991. In#uence of biomass burning emissions on precipitation chemistry in the equatorial forests of Africa. In: Levine, J.S. (Ed.), Global Biomass Burning. Cambridge, MA, MIT Press, pp. 167}174. Lacaux, J.P., Loemba-Ndembi, J., Lefeivre, B., Cros, B., Delmas, R., 1992. Biogenic emissions and biomass burning in#uences on the chemistry of the fogwater and stratiform precipita-
2744
M. Radojevic, K.S. Tan / Atmospheric Environment 34 (2000) 2739}2744
tions in the African equatorial forest. Atmospheric Environment 26A, 541}551. Lacaux, J.-P., Servant, J., Baudet, J.G.R., 1987. Acid rain in the tropical forests of western Africa. In: Perry, R., Harrison, R.M., Bell, J.N.B., Lester, J.N. (Eds.), Acid Rain } Scienti"c and Technical Advances. Selper Ltd, London, pp. 264}269. Nichol, J., 1997. Bioclimatic impacts of the 1994 smoke haze event in Southeast Asia. Atmospheric Environment 31, 1209}1219. Radojevic, M., 1997. The haze in South East Asia. Environmental Scientist 6, 1}3. Radojevic, M., 1998. Burning issues. Chemistry in Britain 34 (12), 38}42. Radojevic, M., Lim, L.H., 1995. A rain acidity study in Brunei Darussalam. Water, Air and Soil Pollution 85, 2369}2374.
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