Analysis of Air Pollutant Emissions for Mechanized Rice Cultivation in Korea

In Korea, rice is a major staple grain and it is mainly cultivated using various types of agricultural machinery. Air pollutants emitted from agricultural machinery have their origins mainly from the exhaustion of internal combustion engines. In this study, the emission characteristics of five main air pollutants by the European Environment Agency’s Tier 1 method for rice cultivation were analyzed. Diesel is a main fuel for agricultural machinery and gasoline is generally used only for rice transplanters as a fuel in Korea. Tractors consume 46% of total fuel consumption and 56% of diesel fuel consumption. Gasoline used for rice transplanters accounts for about 17% of the total fuel consumption each year. Tractors and rice transplanters emit 82% of all total pollutants. From 2011 to 2019, the total amount of air pollutant emissions decreased by 15%. That accounted for the reduction of rice cultivation fields in those periods. Rice transplanting operation accounts for 42% of total emissions. Then, harrowing, harvesting, tilling, leveling, and pest control operations generated 10%, 10%, 8%, 8%, and 7% of total emissions, respectively. The contribution of each air pollutant held 54% of CO, 39% of NOx, 5% of NMVOC, and 2% of TSP from the total emission inventory. The three major regions emitting air pollutants from mechanized agricultural practices were Jeollanam-do, Chungcheongnam-do, and Jeollabuk-do, which consume 55% of the total fuel usage in rice farming. The total amount of air pollutant emissions from rice cultivation practices in 2019 was calculated as 8448 tons in Korea.


Introduction
Rice (Oryza sativa L.) is a globally cultivated species and is the most cultivated crop in many Asian countries [1]. Rice (Oryza sativa L.) is the staple food for four billion people. The top three main rice producers in Asia are China, India, and Indonesia, while Korea is at position 15th in Asia [2,3]. Korea is the one of the largest crop producing countries with 1,643×10 3 ha total arable area for crops and produces a total grain production of 4,375×10 3 tons in 2015 [4,5]. Rice is a staple crop and is cultivated in 730×10 3 ha in 2019 in Korea [4].
Traditionally agriculture produces and consumes energy in one form or another; fossil fuel energy, electric energy, animal power and human power [6]. The amount of energy used in agricultural production has increased intensively because the traditional, low energy input farming is being replaced by modern high energy systems to produce more products efficiently [7]. Agricultural practices including tillage, planting, fertilizer spreading, harvesting etc. were done mostly by various machinery and have been recognized as a significant source of atmospheric particulate matter (PM) and gaseous pollutants which adversely affect human health and regional environment [8,9,10]. Agriculture is an industry that is directly or indirectly affected by climate change while emitting air pollutants through the use of various agricultural machinery in producing agricultural products [11].
Along with the mechanization of agricultural farming in Korea, more animal and human powers that used to be the main agricultural power sources in the past were substituted by agricultural machinery in the recent decades. Most of agricultural practices necessary to cultivate rice have been mechanized; the degree of mechanization is reported to be 98.6% [12]. Air pollutants emitted from agricultural machinery have their origins mainly from the exhaustion of internal combustion engines. Fossil fuels used in internal combustion engines include diesel, gasoline, kerosene, heavy oil, etc. Among them, agricultural machinery uses mainly diesel and gasoline as their fuels in Korea. Given the growing importance of agricultural machinery, researchers started to estimate the emissions at the city, regional or country level [13,14]. The agricultural machinery emissions of NOx, PM10, VOCs and CO were estimated at 16,209, 1,348, 1,933 and 7,097 Mg, respectively, in 2015, and 16,249, 1,330, 1,902 and 7,038 Mg, respectively, in 2018 in Korea [15]. The emissions of agricultural machinery were not negligible even they were not evenly distributed in a whole year. They could be extremely large on preparing fields for seeding or planting and harvesting seasons. When agricultural machines are intensively used, their emissions could be comparable with on-road vehicles and play an important role on air quality [16].
The current agricultural machinery emission inventories were developed based on the machinery activity data (mileage, work output or fuel usage) and corresponding air pollutant emission factors [17,18,19]. The National Institute of Environmental Research (NIER) in Korea published a recommendation to estimate the amount of air pollutants from the use of various agricultural machinery [20]. Many data should be provided to calculate the yearly amount of eight air pollutants from agricultural machinery use. The emission factor, rated power, and load factor data are provided by the NIER handbook. But other data including the number and working hours of each machinery type also are required for calculation process. The European Environment Agency (EEA), on the other hand, adopts a somewhat different approach to calculate the amount of air pollutants from agricultural machinery [21]. Even with different methods developed, there is still a huge gap between current data and the real-world in-use activity. Firstly, the number of agricultural machines owned in a certain area cannot indicate the actual amount of machinery used. During the busy farming season, a large amount of agricultural machinery is rented and used, and some unused agricultural machinery may be included. Secondly, the working environment and utilization rate differ depending on the crop cultivation environment.
The objectives of the study are to analyze emission characteristics of five main air pollutants by EEA Tier 1 method for rice cultivation in Korea from 2011 to 2019 every two year. In addition, the spatial distribution of the amount of five pollutants was visualized by geographic information system (GIS) on country scale.

Materials and Methods
There are several important factors in the calculation of emission inventory.

Calculation of Air Pollutant Emissions
Tier 1 method developed by the EEA was used to calculate air pollutants in the study. As shown in Eq. (1), the calculation of emissions requires fuel consumption used for rice producing and emission factors for each air pollutant emitted from agricultural engines.
where, Ei, j, k is amount of emission of pollutant from agricultural machinery of region; FCi, k is amount of fuel consumption by agricultural machinery of region; EFj is emission factor of pollutant (kg/ton fuel); i is agricultural machinery type (i=1, ···, 4); j is type of air pollutant (j=1, ···, 5); k is region (k=1, ···, 10).

Factors Related to Calculating Amount of Fuel Consumption
About four types of agricultural machines including tractors, power tillers, rice transplanters, and combines, are frequently used for rice cultivation in Korea. The power tiller is a two-wheel tractor, sometimes called a walking tractor, and performed various agricultural operations. The power tiller was an important role in the mechanization of Korean agriculture. The tractors are equipped with various implements such as plow, rotavator, and harrow, etc. and are used for tilling, harrowing, leveling, transportation, etc., and power tillers are currently equipped with small gasoline engines and are mainly used for using in pesticide spreading operation in the study. Rice transplanters and combines are currently equipped with diesel engines. Data on the amount of fuel consumed per rice acreage could be obtained from the relevant literature [22]. Rice cultivation fuel consumption is classified according to the type of machinery and equipment used, and is listed as shown in Table 1. Table 1. Fuel consumption data for machinery and implements used in rice cultivation [22]. The cultivated area of rice by year was searched by the Statistics Korea. It is the rice cultivated area from 2011 to 2019 every two year. As shown in Table 2, rice cultivation areas of studied regions were prepared from 9 provinces and 1 total metropolitan city (TMC) including 8 metropolitan cities in Korea.

Emissions Factors
The emission factors of five air pollutants used in the study are listed in Table 3. They are obtained from the Air Pollutant Emission Inventory Guidebook from EMEP/EEA [21].

Spatial Allocation of Emission
Total amount of emissions calculated in the study was allocated visually to understand the emission characteristics of each region. Emissions of five air pollutants have been assigned to each region and used the QGIS software version (3.10.11). Emissions for agricultural machinery and agricultural work used for rice cultivation are allocated to the vector layer according to the electronic geographic information. Table 4 shows diesel (D) and gasoline (G) fuel consumption of target regions. Gasoline is used only in rice transplanters, and diesel is used for the tractors, power tillers, and combines. Fuel consumption is in the order of Jeollanam-do, Gyeongsangnam-do, and Jeollabuk-do, accounting for 55% of the total fuel consumption for mechanized farming in Korean agriculture.       Figure 3 shows the contribution rate of each agricultural operations to the total emissions of rice cultivation over the past 9 years. Rice transplanting operation was the highest at 42%, harrowing and harvesting operation was 10% each, tilling and leveling operation was 8%, and pest control operation was 7%, followed by that. Analyzing the contribution rate for each air pollutant was CO 54%, NOx 39%, NMVOC 5%, and TSP 2% in that order.   Figure 5, respectively. In general, the areas where rice cultivation emits air pollutants are concentrated in areas with large cultivated filed. Relatively low emissions are generally distributed in areas with low population densities and low rice production. In addition, economically developed large cities emit less air pollutants due to less agricultural activity.

Conclusions
In this study, we calculated and analyzed five air pollutants emitted from four agricultural machinery from 2011 to 2019 in Korea. The total amounts of fuel consumed annually of tractors, power tillers, rice transplanters, and combines were calculated to estimate air pollutant emissions. Also, the amount of fuel consumed by 9 regions were analyzed. Total yearly fuel consumption from 2011 to 2019 was calculated as 139.5 Ml, 136,1 Ml, 130.6 Ml, 123.3 Ml, 119.3 Ml, respectively. Tractors consumed 46% of the total fuel used for rice production. Rice transplanting operation generated the highest air pollutant emissions among various agricultural operations. Also, it was found rice transplanters were the main source of CO emission. As a result of analyzing air pollutants emitted by region, Jeollanam-do, Chungcheongnam-do, and Jeollabuk-do were main regions. From 2011 to 2019, air pollution emissions emitting from rice cultivation was decreased by 15%. It is presumed that the rice cultivation areas decreased, so did air pollutant emissions.
The results of analysis of air pollutants emissions in this study can improve the air quality management of local areas. It can contribute to establish effective policies to manage energy consumptions and to protect the health of farmers.