In 2017, the Food and Agriculture Organization of the United Nations (FAO) reported that there were 102 countries with sugarcane cultivation, with a total of 26 million hectares (Mha) of sugarcane-cultivated land, and a total of 1842 million tons (Mt) of fresh sugarcane produced. The country that produced the most sugarcane was Brazil, which could produce up to 759 Mt (equivalent to 41% of total sugarcane), followed by India and China, which produced 306 Mt (17%) and 104 Mt (6%) respectively. Thailand was the fourth largest sugarcane producer, producing 103 Mt of sugarcane (6%) [1
According to a report by the Office of Cane and Sugar Board (OCSB), in the production year 2018/2019 [2
], Thailand had a total area of 2.0 Mha to produce fresh sugarcane as raw materials for 131 Mt. The sugarcane purchased from farmers by sugar factories was divided into fresh sugarcane and burned sugarcane, accounting for 51 Mt or 39% of total sugarcane and 80 Mt or 61% respectively. As of 2019, there were 56 sugar factories in operation in Thailand, producing a total of 1.46 Mt of sugar. Normally, sugar factories purchase sugarcane around late November to late April every year, which takes approximately 94−166 days depending on the production capacity and quantity of sugarcane around the area of each factory.
According to the information from the production season 2018/2019 [2
], the sugar production process produces about 5.88 Mt of molasses (accounting for 44% of sugarcane raw material) and 48.4 Mt of bagasse (accounting for 37% of sugarcane raw materials). Molasses is used as raw material for ethanol production, while about 49% of bagasse is used as fuel to generate heat in sugar factories. The other 51% of the bagasse is used as fuel in thermal power plants. It can be seen that the agricultural waste produced in the production process is sufficient to be used as fuel for heat production in sugar factories, but the waste agricultural residues in cultivated areas, namely the sugarcane tops and leaves, have not been utilized in the energy sector.
Farmers usually burn sugarcane tops and leaves before harvesting to ease the cutting and transporting of sugarcane logs to sugar factories, even though the price paid at sugar factories for burned sugarcane is lower. In the production year 2018/19 [3
], 1 United States Dollar (USD) (1 USD ~ 30.5 baht) was deducted for one ton of burned sugarcane sent to a sugar factory. Seventy per cent of the money was paid to farmers who sold fresh sugarcane to the factory, and the remaining 30% was paid to the farmers who sold burned sugarcane. Nevertheless, considering the reduction of labor costs in harvesting, most farmers still prefer to burn sugarcane tops and leaves before harvesting.
The high rate of preharvest sugarcane burning has been affecting the air quality in the surrounding area. Information has been collected in three monitoring stations located in the provinces with a lot of sugarcane cultivation area [4
], namely Kanchanaburi Meteorological Station (79T) in Kanchanaburi province (harvested area in 2018 = 115 kilo hectares (kha)), the Regional Water Resources Office Station 4 (46T) in Khon Kaen province (102 kha), and the Regional Environment Office Station 8 (26T) in Ratchaburi province (29 kha) (Figure A1
). According to the air quality measurement data gained from these stations, the monthly average of PM2.5
concentration in 2018 until June 2019 was in the range of 39−60 micrograms per cubic meter (µg/m3
) during the time when sugar factories were open to buy sugarcane, and the monthly average PM2.5
was between 8−20 µg/m3
during the period when sugar factories were closed for buying sugarcane (Figure A2
a). While, the World Health Organization (WHO) advises that the annual average PM2.5
value should not exceed 10 µg/m3
, and the average amount in 24 hours should not exceed 25 µg/m3
]. Figure A2
b shows the number of days in each month with PM2.5
exceeding 24-h mean concentration guideline levels. During the months when sugar factories were open to buy sugarcane, it can be seen that the 24-h PM2.5
concentration average was higher than the WHO guidelines levels in all three stations. However, please note that the daily average variation of particulate matter concentration is also related to the meteorological factors, such as relative humidity, temperature, and wind speed [7
The concentration of PM2.5
that exceeds the guidelines levels has been affecting human health. The Bureau of Occupational and Environmental Diseases (BOED), the Ministry of Public Health, Thailand [9
], has reported that in the northern region of Thailand, the number of patients hospitalized with chronic diseases of the lower respiratory tract (ICD−10 Code J40−J47) increased significantly between January and April, which was the time when the particles with a diameter of 10 microns or less (PM10
) and PM2.5
value exceeded the guidelines levels for the 24-h average due to agricultural biomass burning and forest fires.
In addition, according to a report by José, C. et al. [10
], air pollution from preharvest sugarcane burning in 1997−1998 affected the respiratory systems of children and the elderly. The increase in PM2.5
to 10.2 µg/m3
and the increase in PM10
to 42.9 µg/m3
has caused an increase in the number of children and the elderly diagnosed with respiratory diseases, approximately 21.4% and 31.03% respectively. The impact was higher during the time that sugarcane was burned than during the time of no burning. The information corresponds with a research by Silveira, H. et al. [11
], which reported that the sugarcane burning during the harvest period affected the health of workers in sugarcane cultivation in Brazil. Also, according to Nicolella, A.C. and Belluzzo, W. [12
], the reduction of preharvest sugarcane burning area brought about a decline in the number of patients in São Paulo, Brazil, and their study also found that the effects of fine particles from preharvest sugarcane burning had more health impacts than other emissions sources, such as transportation and industry.
The FAO has evaluated the amount of burned sugarcane biomass by setting the default value of the proportion of the burned sugarcane biomass per sugarcane yield to 0.65 for every country [13
]. From the FAO’s data, it is roughly projected that in 2017, a total of 16.9 Mt of sugarcane biomass was burned worldwide, emitting 1.3 Mt of CO2
, 45.6 kilotons (kt) of CH4
, and 366 kt of N2
O. It can be seen from these results that the countries with the most sugarcane biomass burning are listed in order of their sugarcane production capability. However, there are other factors influencing preharvest sugarcane burning such as the size of the plantation, the harvest method (use of machinery or human labor), labor costs, the amount of labor in each country, and environmental laws.
Evaluation of air emissions from preharvest sugarcane burning has been done in many countries with the highest sugarcane cultivation such as Brazil. Daniela, F. et al. [14
] studied in São Paulo, the city with the most sugarcane cultivation in Brazil, by using remote sensing data to evaluate the burned area. The study reported that during 2006−2011, São Paulo had annual average air emissions from preharvest sugarcane burning as follows: 1130 kt of CO, 26 kt of NOX
, 16 kt of CH4
, 45 kt of PM2.5
, 120 kt of PM10
, and 154 kt of NMHC (nonmethane hydrocarbons).
In Thailand, Sornpoon, W. et al. [15
] conducted an experiment by burning sugarcane biomass in 13 sugarcane plantations to study the amount of air pollution from the burning of biomass per unit area. The results showed that the sugarcane plantation areas had average air emissions per area of 766 grams per square meters (g/m2
) of CO2
, 46.5 g/m2
of CO, 1.4 g/m2
, 0.04 g/m2
O, and 1.3 g/m2
. In addition, Kim Oanh, N.T. et al. [16
] conducted air pollution assessments from crop residue burning in Southeast Asia (SEA) from 2010−2015, the study set SEA countries’ percentage of sugarcane residue subjected to open burning at 55% of total biomass production.
Because Thailand’s air quality exceeded the health standard, especially the PM2.5
concentration, on June 11, 2019, the Cabinet acknowledged this and agreed with the Ministry of Industry’s proposed measure to solve the burned sugarcane problem in Thailand by law enforcement [17
]. That is, in the production season of the year 2019/20, the amount of burned sugarcane accepted by sugar factories cannot exceed 30% of total sugarcane per day, while in the production season of 2020/21, sugar factories can accept not more than 20% burned sugarcane per day, and in the production season 2021/22 the amount of burned sugarcane to be accepted will be reduced to 0−5% per day. This will eliminate burned sugarcane within three years.
Therefore, the situation of air emissions from preharvest sugarcane burning and the spatial and temporal distribution of sugarcane burning in each province are necessary pieces of information for effective planning and implementation of the measure, and the integration of information in all relevant sectors is as important. This study calculated the preharvest sugarcane burning emissions inventories during the production seasons 2007/08−2018/19 and estimated future air pollution emissions by comparing the amount of air pollution emissions in the scenario of preharvest sugarcane burning in usual business (business as usual or BAU) and in the scenario of the implementation of the government’s measure to reduce burned sugarcane in the next four production seasons (2019/20−2022/23). Moreover, the results also include a map of spatial and temporal distribution of air emissions from preharvest sugarcane burning in Thailand to be used as a database of air quality modelling and management work.
In this study, the researchers have selected the appropriate value for each variable related to the evaluation of air pollution from preharvest sugarcane burning by reviewing numerous past studies that are suitable for the Thailand context. The results showed that, during the production seasons 2007/08−2018/19, burned sugarcane in Thailand tended to continuously increase, resulting in more air pollution, and it can be predicted that air emissions will continue to increase in the future. That is, in the production season 2022/23, the amount of emissions is expected to increase by approximately 21% compared to that in the production season 2018/19. However, if the government enforces the sugarcane burning reduction measure during the production seasons 2019/20−2022/23, farmers must immediately reduce preharvest sugarcane burning, which will reduce the amount of air emissions compared to BAU in each year by 53%, 69%, 92%, and 100% respectively.
The results also showed the differences between the use of the top-down approach and the bottom-up approach to evaluate burned area. That is, the bottom-up approach gave approximately a three times higher value of the burned area than the top-down approach did. Therefore, when using the value gained from the top-down approach in evaluating the air emissions, the results may be lower than the fact. However, the satellite can be used to monitor the spatial and temporal distribution of sugarcane burning adequately.
Finally, all the results should be useful for those who are involved in energy and environmental policies and agricultural economic policies to make effective decisions. Furthermore, in order to improve Thailand’s air quality in the future, the government should also have measures to reduce other types of biomass burning, especially rice straw biomass, which is also considered as a source of air pollution like sugarcane tops and leaves biomass. The government should also support the use of sugarcane tops and leaves biomass materials in the renewable energy sector, which could help farmers earn income from selling biomass scraps and to help reduce their cost of harvesting.