1. 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 one of the largest crop producing countries with 1643 × 10
3 ha of total arable area for crops and generated a total grain production of 4375 × 10
3 tons in 2015 [
4,
5]. Rice is a staple crop and it was cultivated in 730 × 10
3 ha in 2019 in Korea [
4].
Traditionally, agriculture produces and consumes energy in one form or another, such as 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 types of 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,
11,
12,
13,
14,
15,
16,
17,
18]. Agriculture is an industry that is directly or indirectly affected by climate change while emitting air pollutants through the use of various types of agricultural machinery in producing agricultural products [
7].
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 of rice production was reported to be 98.6% in 2020 in Korea [
19]. 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 [
20,
21]. The agricultural machinery emissions of NOx, PM
10, VOCs, and CO were estimated at 16,209, 1348, 1933, and 7097 tons, respectively, in 2015, and 16,249, 1330, 1902, and 7038 tons, respectively, in 2018 in Korea [
22]. The emissions of agricultural machinery were not negligible even though 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 [
23].
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 [
24,
25,
26]. The National Institute of Environmental Research (NIER) in Korea published a recommendation to estimate the amount of air pollutants from the use of various types of agricultural machinery [
27]. A large number of 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. However, other data including the number and working hours of each machinery type also are required for the 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 [
28]. 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 were to analyze the emission characteristics of five main air pollutants by the EEA Tier 1 method for rice cultivation in Korea from 2011 to 2019 every two years. In addition, the spatial distribution of the amount of five pollutants was visualized by a geographic information system (GIS) on a country scale.
4. Conclusions
In this study, we calculated and analyzed five air pollutants emitted from four types of agricultural machinery from 2011 to 2019 in Korea. The total amounts of fuel consumed annually of tractors, power tillers, rice transplanters, and combine harvesters were calculated to estimate air pollutant emissions. Additionally, the amount of fuel consumed by nine regions was analyzed. The total yearly fuel consumption from 2011 to 2019 was gradually decreased from 139,515 tons to 119,252 tons of diesel and gasoline fuels. Tractors consumed 46% of the total fuel used for rice production. Rice transplanting operation generated the highest air pollutant emissions among various agricultural operations. It was also found that rice transplanters were the main source of CO emissions. The regions with larger air pollutants are Jeollanam-do, Chungcheongnam-do, and Jeollabuk-do. From 2011 to 2019, air pollution emissions emitting from rice cultivation decreased by 15%. It is presumed that the rice cultivation areas decreased, and so did air pollutant emissions.
The results of the analysis of air pollutant emissions in this study can improve the air quality management of local areas. Further study is needed to sophisticate the emission inventory in rice production using a more advanced methodology such as a Tier 2 method and more.