Comparison of Diesel Tractor Emissions in Korea

: Due to the shortage of agricultural labor forces and rapid aging of farmers, the utilization of tractors is becoming popular and essential in Korea. Tractors can be classified into two types, a walking tractor called as a power tiller and a riding tractor. In this study, agricultural tractors including walking and riding types were categorized into 4 levels by rated output power. And diesel emission inventory of tractors was established and analyzed using 2011 and 2019 survey data in Korea. Emission inventory including CO, NOx, SOx, TSP(PM 10 ), PM 2.5 , VOCs and NH 3 were established using Tier 3 methodology. The total amount of emission using agricultural tractors was decreased about 13% from 2011 to 2019. The number of walking tractors were decreased by about 19% in 8 years, on the other hand that of riding tractors were increased by about 12%. However, the emission reduction is about 48% for walking tractors and the emission increment is about 5% for riding tractors. Thus, the total emission from agricultural tractors was decreased by about 16% in those periods. It is due to the decrease of 21% and 15% in the hours of use of walking and riding tractors, respectively, in 2019. Walking tractors mainly emit air pollutants from spraying and transporting. Riding tractors mainly 61% of total air pollutants emits from soil preparation and transporting operations. Geographic information system (GIS) was used to spatially assign air pollutants variables into 17 provinces and metropolitan cities in Korea. High emission generating regions and changes of emissions during 8 years were clearly seen in GIS analysis. High air pollutant emitting regions are mainly located in the western and southern regions of Korea, which have plenty of arable areas compared to other regions in Korea.


Introduction
In 2019, the total cultivated land in Korean was 1,643,465 ha, and the amount of production was 4,375x10 3 tons, 8,186 x10 3 tons, 2,206 x10 3 tons and 65 x10 3 tons of grain crops, vegetables, fruits, and specialty crops, respectively [1,2]. Due to the decline of agricultural labor forces and rapid aging of farmers, the utilization of agricultural machinery is becoming popular. Recently, there is a trend that farmers are utilizing bigger size tractors comparing to 2010 in Korea [3]. The mechanization rate of rice farming is more than 99%, and that of the other major agricultural works in open field farming is about 62% in average in 2019 [4].
Tractor is a multi-purpose vehicle that performs major agricultural operations while driving with various implements such as a plow, a rotary, or a baler, and is frequently used in Korean agriculture [5,6]. Tractors are used to do many agricultural practices such as tillage, harrowing, fertilizer and compost spreading, and transportation in almost every agricultural sector of grain, vegetable, fruit production, and livestock husbandry. Tractors usually use a diesel as a fuel and emit a lot of pollutant substances which are primary and secondary sources of particulate matter (PM) and the other air pollutants. PM is considered as one of the most concerning air pollutants due to its effect on human health and environment both in urban and rural area [7,8,9,10,11,12,13]. The non-road mobile machinery sector including tractors largely contributes to the emissions of PM10 and PM2.5, being responsible for 7.4% and 16.4% of the total emissions respectively [14].
An emission inventory can show the temporal and spatial distributions and changes in pollutants in a certain area over a period of time. Currently, the global level non-road machinery activities and emission data are difficult to obtain, and the development of emission models and inventories is still being undertaken. Only the NONROAD model, developed by the U.S. Environmental Protection Agency (EPA), has been widely used [15].
Mobile sources can exhaust many kinds of pollutants including sulfur dioxide (SO2), nitrogen oxides (NOx), total hydrocarbons (THC), carbon monoxide (CO) and particulate matter (PM)) during the process of fuel combustion. These pollutants can cause direct or indirect adverse influences to air pollution [16,17,18], human health [19,20] and climate change [21,22,23]. For example, emitted PM could directly increase atmospheric particulate matter with a diameter below 2.5 μm (PM2.5) concentrations; as important fine particle precursors, SO2 and NOx can transform into sulfate and nitrate, making a secondary contribution to the PM2.5 [24,25].
In this study, a diesel emission inventory for agricultural tractors including 2 wheeled driving (2WD) and 4 wheeled driving (4WD) tractors was established and analyzed using 2011 and 2019 data in Korea by categorizing tractors in terms of their rated powers. Also, emission characteristics of seven air pollutants from various field operations was analyzed. In addition, the spatial distribution of the amount of eight pollutants was visualized by geographic information system (GIS) and was investigated on country scale.

Calculation of Air Pollutant Amount Emitted from Farm Tractor Operation
Emitted amounts of seven air pollutant substances due to tractor operation were calculated by the method of NIER [26]. The formula is shown in Equation (1): where, Ei,j,k is Total amount of air pollutant emitted from specific region (kg/yr); Ni,k is Number of machinery of specific region (unit); HPi is Average rated power of tractor (kw); LF is Load factor (=0.48); HRSi is Average annual activity of tractor (hr/yr); EFi,j is Emission factor (kg/(kWh-unit)); i is Farm tractor type (walking, riding)(i=1, ···, 4); j is type of air pollutant(j=1, ···, 8); k is region(k=1, ···,10).

Number of Farm Tractors
In agricultural machinery statistic data from the Ministry of Agriculture, Food and Rural Affairs (MAFRA) in Korea, the number of agricultural tractors were categorized into two groups, a power tiller so called as a walking 2WD tractor and a farm tractor known as a riding 4WD tractor. The farm tractor group contains three subgroups, small, medium, large, categorized by tractor's engine rated powers. The Table 1 shows statistic data of tractors used in Korean agriculture in 2011 and 2019. Table 1 shows the number of tractors each year in Korea. Table 2 shows the average rated powers of diesel tractors used for calculating diesel emissions.

Average Annual Operating Hours of Farm Tractor
Average annual operating hours are given in Table 3 according to tractor types as well as some typical agricultural practices. Survey data by the Rural Development Administration (RDA) on the utilization of agricultural machinery were used to identify the average annual operating hours of agricultural tractors [4,27].  Table 4 shows emission and fuel factors required to calculate the amount of six air pollutants emitted from agricultural tractors.

Visualization of Emissions
To calculate the domestic spatial distribution of total air pollutant emissions from tractors, an open source geographic information system (GIS) software (QGIS, Windows 10 version) was used. The total of 9 provinces and 1 total metropolitan city (TMC) including 8 metropolitan cities was analyzed in the study. Based on the geocoded residential addresses, individual exposure to the various variables was assessed applying GIS program. QGIS is a widely-used, open-source GIS visualization tool that allows users to produce, edit, visualize and analyze spatial data. It supports vector and raster format, as well as a database format and functionalities (QGIS, 2021).

Total Emissions of Agricultural Tractors
The air pollutant emission inventory for agricultural tractors in 2011 and 2019 in Korea was calculated. Tables 5 and 6 show that the amount of air pollutants emitted from various agricultural practices from agricultural tractors. The two main sources of air pollutants emitted from walking tractor are transporting and spraying. They emit about 81% of emission from waling tractors. Riding tractors are heavily used in soil preparation, which emits about 42% of air pollutants, including tilling, harrowing and leveling, for seeding and planting in Korea. Figure 1 shows the change of calculated total emissions in agricultural tractors categorized into 4 groups. The total amount of emission using agricultural tractors was decreased about 13% from 2011 to 2019. The number of power tillers were decreased by about 19% in 8 years, on the other hand that of farm tractors were increased by about 12%. However, the emission reduction is about 48% for power tillers and the emission increment is about 5% for farm tractors. Thus, the total emission from agricultural tractors was decreased by about 16% in those periods. It is due to the decrease of 21% and 15% in the hours of use of walking and riding tractors, respectively, in 2019. However, the total amount of air pollutants emitted from large size riding tractors was increased by about 33% in 2019. Recently, Korean farmers are showing a tendency of using large size riding tractors to reduce working hours in the fields.

Air Pollution Emissions from Farm Tractor Operations
The diesel emission inventory for agricultural tractors in Korea was refined by categorizing the rated power of riding tractors into 3 sub-groups. Figures 2 and 3 show that calculated amounts of average air pollutants emission from various agricultural operations by walking and riding tractors, respectively. Walking tractors mainly emit air pollutants from spraying and transporting. In particular, in the case of transporting, 2,639 Mg of air pollutants was emitted in 2011 and 1,429 Mg of air pollutants was emitted in 2019. Riding tractors mainly emit air pollutants from soil preparation and transporting operations. About 61% of total air pollutants are emitted from those operations. Particularly air pollutant emission from loading in 2019 was nearly doubled compared to 2011. Korean farmers are using riding tractors as loading heavy material recently.

Spatial and Temporal Distribution of Air Pollutant Emissions
The amount of air pollutants emitted by Korean agricultural tractors was calculated on a region-level. Tables 7, 8 100  199  5  20  18  30  6  349  CHN 2  192  384  10  38  35  58  11  673  GAW 3  85  171  5  17  16  26  5  299  GYB 4  306  613  16  61  56  92  18  1,074  GYG 5  129  258  7  26  24  39  8  453  GYN 6  195  390  10  39  36  58  11  684  JEB 7  133  265  7  27  24  40  8  465  JEJ 8  32  65  2  6  6  10  2  114  JEN 9  232  464  12  46  43  70  14  814  TMC 10  64  128  3  13  12  19  4  225  Total  1,469 2,940  78  296  270  441    The spatial distribution of the total amount of tractor air pollutant emission in Korea were visualized at the region-level using a GIS technique, as shown in Figures 4 and 5. Figure 4 Figures 4 and 5 show that the emission of the walking tractor is decreasing, but the emission of the riding tractor is increasing in Gyeongsangbuk-do region. In 2011, riding tractor emissions were in about same range in Chungcheongnam-do, Gyeongsangbuk-do, Gyeonggi-do, and Jeollanam-do, but in 2019, the emission range in Gyeongsangbuk-do, Jeollanam-do, Chungcheongbuk-do and Jeollabuk-do increased by one level. These high-emission areas are mainly located in the western and southern regions of Korea, which have plenty of arable areas compared to other regions in Korea. However, riding tractor emissions are much lower in Gangwon-do and Chungcheongbuk-do. This area is mainly mountainous, so there is little agricultural area to produce agricultural products. Metropolitan cities with high population generate less emissions from agricultural tractors compared to other regions.

Conclusions
In this study, agricultural tractors including walking and riding types were categorized into 4 levels by rated output power and diesel emissions of tractors were analyzed using 2011 and 2019 survey data in Korea. Emission inventory including CO, NOx, SOx, TSP(PM10), PM2.5, VOCs and NH3 were established using Tier 3 methodology. As a result, the annual emissions of CO, NOx, SOx, TSP(PM10), PM2. 5 The total amount of emission using agricultural tractors was decreased about 13% from 2011 to 2019. The number of walking tractors were decreased by about 19% in 8 years, on the other hand that of riding tractors were increased by about 12%. However, the emission reduction is about 48% for walking tractors and the emission increment is about 5% for riding tractors. Thus, the total emission from agricultural tractors was decreased by about 16% in those periods. It is due to the decrease of 21% and 15% in the hours of use of walking and riding tractors, respectively, in 2019. Walking tractors mainly emit air pollutants from spraying and transporting. In particular, in the case of transporting, 2,639 Mg of air pollutants was emitted in 2011 whereas 1,429 Mg of air pollutants was emitted in 2019. Riding tractors mainly emit air pollutants from soil preparation and transporting operations. About 61% of total air pollutants are emitted from those operations. High emission generating regions and changes of emissions during 8 years were clearly seen in GIS analysis. High air pollutant emitting regions are mainly located in the western and southern regions of Korea, which have plenty of arable areas compared to other regions in Korea.