Analysis of the National Air Pollutant Emission Inventory (CAPSS 2015) and the Major Cause of Change in Republic of Korea

In 2015, air pollutant emissions in the Republic of Korea were 792,776 metric tons of CO, 1,157,728 metric tons of NOx, 352,292 metric tons of SOx, 604,243 metric tons of TSP, 233,177 metric tons of PM10, 98,806 tons of PM2.5, 15,934 metric tons of BC, 1,010,771 metric tons of VOCs, and 297,167 metric tons of NH3. Among major emission source categories, the main emission sources and the contributions to emissions, by pollutant, were as follows: road transport (31.0%), biomass burning (29.3%), and non-road transport (17.1%) for CO; road transport (31.9%), non-road transport (26.3%), and manufacturing industry (14.6%) for NOx; industrial processes (29.9%), energy production (25.9%), and manufacturing industry (24.2%) for SOx; fugitive dust (67.6%) manufacturing industry (20.1%) for TSP; fugitive dust (47.0%) and manufacturing industry (30.4%) for PM10; manufacturing industry (36.8%), fugitive dust (17.5%), and non-road transport (14.3%) for PM2.5; road transport (42.0%) and non-road transport(39.6%) for BC; solvent use (54.9%) and industrial processes (18.1%) for VOCs; and agriculture (77.8%) and industrial processes (13.3%) for NH3. The data we calculate can be used as official national emissions data for the establishment, implementation, and assessment of air quality-related policy, such as measures to deal with particulate matter, as well as for related modeling and other research.


INTRODUCTION
Estimating air pollutant emissions data is vital for informing policy and research to improve the atmospheric environment.However, it is a delicate issue due to the various politico-economic interests involved.Nevertheless, this data is needed to establish policies for atmosphere management and to counter climate change and is an important tool for policy setting and outcome assessment (National Institute of Environmental Research, 2018).
Looking at the state of emissions in two developed countries, in the United States, the Environmental Protection Agency (EPA) compiles and publishes the National Emission Inventory (NEI), focusing on general air pollutants and hazardous air Analysis of the National Air Pollutant Emission Inventory (CAPSS 2015) and the Major Cause of Change in Republic of Korea pollutants (HAPs).Alternatively, Japan does not have an official unified national inventory, and emissions from each emission source are estimated by the institution with convenient access and control of data.For example, the emission data in JEI-DB is compiled by the Japan Auto-Oil Program ( JATOP), which is an inventory program combining emission sources estimated and managed by each institution, emission sources calculated directly from statistical data using equations, and emission sources estimated using approximate emission models (National Institute of Environmental Research, 2018).
In the Republic of Korea, the National Institute of Environmental Research (NIER) estimates the annual emissions of the air pollutants, CO, NO x , SO x , TSP, PM 10 , PM 2.5 , BC, VOCs, and NH 3 , via the Clean Air Policy Support System (CAPSS).To this end, around 300 data points are collected from 150 domestic institutions (as of 2015 emissions).Emissions are calculated by applying the emissions factors and control efficiency for each emission source/fuel to the appropriate activity level for each emission source (bottom-up only).
The estimated emissions amounts play the role of the official air pollutants emissions data for the Republic of Korea, which are then used as basis to establish and analyze the expected effects of policies for air improvement, such as the combined air improvement plan, the basic plan for atmospheric environment management in the capital, special measures against particulate matter, and combined measures to control particular matter.It is also used as input data for air quality prediction models.Thus, alongside air pollution monitoring network data, emissions data is the most important basic data.
In this report, we describe the results of 2015 emissions estimates and analyze the major factors contributing to changes from 2014.

1 Emission Source Classification and Emission Factors
To estimate national air pollutant emissions data, we established an emission source classification system by combining the CORINAIR classification system from Europe with the domestic industrial classification system for air pollutant emission sources.Thus, we classifi-ed emission sources into energy production, non-industry, manufacturing industry, industrial processes, energy transport and storage, solvent use, road transport, nonroad transport, waste, agriculture, other, fugitive dust, and biomass burning (National Institute of Environmental Research, 2013).
Emission factors are displayed as emissions per unit activity.We primarily used emission factors developed from domestic research, including scientific research institutes, and we also referred to emission factors from the EU CORINAIR and the US EPA as necessary (National Institute of Environmental Research, 2015).

2 Method for Emissions Estimation
Emissions were estimated using the appropriate activity levels and emission factors for each emission source.Among emission sources, point pollution sources were estimated using a bottom-up method, based on data collected from the Stack Emission Management System (SEMS) and CleanSYS (remote stack monitoring system), while non-point pollution sources were estimated using a top-down method, using activity levels for each emission source based on statistical data from related institutions, such as fuel consumption and vehicle kilometers traveled (VKT).From these emissions, regional emissions were estimated by a spatial allocation based on factors such as SEMS coordinates and addresses for industrial sites or traffic volume for roads (National Institute of Environmental Research, 2013).

3 Record of Major Improvements in Emissions
The methodology for estimating air pollutant emissions was reviewed by an emission factors committee based on relevant domestic and overseas research results.NH 3 was added to the list of substances for emissions estimation in 2001.In 2005, the state of environmentally-friendly road use was applied to emissions in the capital.In 2007, CleanSYS emissions data were applied, using real-time stack emissions data in CAPSS, and additional emissions were estimated in relevant sectors after the collection of newly imported anthracite coal data.Fugitive dust, a new emission source, was also estimated.In 2011, biomass burning was added as an emission source, and PM 2.5 was added to the list of substances for which emissions are estimated.(In 2015, Biomass burning and fugitive dust emissions were released to the public.But in this paper, the previous emission data of biomass burning and fugitive dust were presented for the consistent analysis.)In 2014, the NO x emission factors were developed and implemented to reflect the actual road driving conditions of diesel vehicles (National Institute of Environmental Research, 2018).Furthermore, past emissions estimates were updated using the latest methodology in the event of major changes in emissions due to the addition of new substances or the discovery of new emission sources, in order to improve the consistency of emission trends analysis.

1. 1 Emissions per Substance and Emission Source
In 2015, the nationwide emissions of air pollutants  1).

1. 2 Emission Trends and Cause of Changes
Although air pollutant emissions have been estimated since 1999, comparisons with past data are difficult due to annual additions of new emission sources or improvements in estimation methods.Since 2007, anthracite coal imports were added to the emissions estimate, CleanSYS emissions data were used, and the VOCs' emission factors were changed, resulting in large shifts in emissions for the related substances.In 2011, improvements to emission estimates continued to be pursued, with the addition of PM 2.5 emissions and new emission sources such as industrial processes, improvement of the car emission factors for transport, and use of control efficiency due to oil mist collection facilities in the energy transport and storage sector.In 2012, the estimation methodology was improved in the non-road transport (construction machinery) sector, and the food and drinks manufacturing (whiskey and other spirits) and VOCs emission factors were improved.In 2014, fishing vessels and leisure boats were added to the ships sector, and the methodology for the roads sector was also improved, such as using NO x emissions factors that reflects the actual road driving conditions.In this report, we present emissions over the last 5 years, from 2011 to 2015, and analyze and describe the main causes of change from 2014 to 2015.The major trends in air pollutant emissions are described below.

CO Emissions
The annual trends in CO emissions are shown in Fig. 2 and Table 2; recently, there has been an overall decrease in emissions.Road transport emissions, which accounted for 31.0% of CO emissions in 2015, decreased by 35,709 metric tons (12.7%) compared to the previous year.This was the result of a 10.5% reduction in vehicle kilometers traveled (VKT) by small passenger cars (2014: 13.624 billion km → 2015: 12,195 billion km).In the non-industry category, which also accounts for a high percentage of CO emissions, use of anthracite coal for heating decreased by 9.6% compared to the previous year (2014: 1,628,911 metric tons → 2015: 1,473,094 metric tons), leading to a 5.6% (4,295 metric tons) decrease in emissions.In the energy production category, emissions decreased 4.7% (2,718 metric tons); this was due to a 19.5% decrease in emissions in the public power generation category, the result of a 42.4% decrease in LNG consumption (2014: 12.210943 billion m 3 → 2015: 7.038176 billion m 3 ).Conversely, in the non-road transport category, CO emissions increased 17.1% (9,597 metric tons) compared to the previous year due to an increase in the mean operating rate of construction machinery (2014: 40.71% → 2015: 41.55%).

NO x Emissions
The annual trends in NO x emissions are shown in Fig. 3 and Table 3; in the last 5 years, there has been an overall increase in emissions.In 2015, NO x emissions increased 13,220 metric tons compared to the previous year.This was due to increased emissions in the non-road  On the other hand, energy production, which accounts for 13.0% of total NO x emissions, decreased 7.4% (12,000 metric tons) relative to the previous year.This appears to be due to a 42.4% decrease in LNG usage at public power generation facilities (2014: 12.210943 billion m 3 → 2015: 7.037176 billion m 3 ) and a 15.4% decrease in LNG usage at district heat production plants (2014: 2.367650 billion m 3 → 2015: 2.003366 billion m 3 ).Manufacturing industry, which accounts for 14.6% of emissions, also decreased by 2.6% (4,521 metric tons) compared to the previous year; this was due to decreases in anthracite coal (2014: 1.961 million metric tons → 2015: 1.281 million metric tons) and LNG usage (2014: 4.694507 billion m 3 → 2015: 3.196508 billion m 3 ), which are included in the 'Other' subcategory for this emission source.

SO x Emissions
As shown in Fig. 4 and Table 5, SO x emissions, which are heavily affected by the sulfur content of fuel, showed an overall decreasing trend (2011: 434,113 metric tons → 2015: 352,292 metric tons).However, in 2015, emissions increased by 9,131 metric tons compared to the previous year.Due to the continual expansion of low sulfur fuel supply policies and clean fuel use policies, fuel's sulfur content has been decreasing, including die-   1,049,435 1,084,383 1,099,723 1,144,508 1,157,728 1.2% (units: metric tons/year) sel, kerosene, and gasoline (Table 4).This has resulted in decreasing SO x emissions in the fuel combustion categories, such as energy production and non-industry, as well as the transport categories.
In 2015, emissions from industrial processes, which accounted for 29.9% of total SO x emissions, increased 6.5% (6,458 metric tons) compared to the previous year.This was due to an emissions increase of 20.1% (5,938 metric tons) in the iron and steel industry, which was the result of increased CleanSYS emissions from some sites (CleanSYS SO x emissions from the pertinent sites, 2014: 8,403 metric tons → 2015: 10,473 metric tons).Non-industry emissions increased 16.5% (4,068 metric tons) compared to the previous year; this was because of a 21.6% increase (2014: 2.012 million kL → 2015: 2.448 million kL) in Bunker-C fuel oil (4.0%) usage at commercial and public institutions.Manufacturing industry accounts for 24.2% of total SO x emissions and increased by 2.5% (2,116 metric tons) compared to the previous year.This was due to an 8.6% increase (2014: 6.500 million metric tons → 2015: 7.058 million metric tons) in the use of anthracite coal for industrial purposes, such as iron and steel, cement, and other uses.
On the other hand, emissions in the Energy production category, which account for 25.9% of total emissions, decreased 3.5% (3,319 metric tons) compared to the previous year.This was due to a 1.6% increase (2014: 79.608 million metric tons → 2015: 80.860 million metric tons) in the use of bituminous coal at public power generation plants.

Particulate Matter (TSP, PM 10 , PM 2.5 , BC) Emissions
Among particular matter, PM 2.5 emissions were first estimated and reported in 2011, and black carbon (BC) emissions were first estimated in 2014.In terms of PM 2.5 , manufacturing industry, which accounts for 36.8% of total PM 2.5 emissions, increased 19.8% (5,996 metric tons) compared to the previous year; this was due to an 8.6% increase (2014: 6.500 million metric tons → 2015: 7.058 million metric tons) in the use of anthracite coal for industrial purposes, such as iron and steel, cement, and other uses.Non-road transport, which accounts for 14.3% of total PM 2.5 emissions, increased by 3.2% (435 metric tons) compared to 2014.This was due to a 3.6%  (units: metric tons/year) increase in the number of registered construction machines (Table 6), and an increase in construction machinery's mean operating rate (2014: 40.71% → 2015: 41.55%).
On the other hand, road transport emissions, which accounted for 8.9% of total emissions, decreased 4.4% (401 metric tons) compared to the previous year, due to a decrease of 23.5% (2014: 5.248 million km → 2015: 4.016 million km in the VKT of small passenger cars.In addition, emissions from energy production decreased by 2.0% (72 metric tons), which was due to a decrease in the use of combined-cycle power (2014: 111,711 Gwh → 2015: 100,598 Gwh).(units: metric tons/year) Fig. 7. Trends in PM 2.5 emissions, by emission source, in the last 5 years.

VOCs Emissions
The annual VOCs emission trend is shown in Fig. 9 and Table 11; the change in emissions resulted from changes in coating usage, and improvements in emissions lists and the emission factors.In 2015, emissions increased due to increases in the categories of waste and solvent use.Emissions from solvent use, which accounted for the largest portion of total emissions (54.9%), in-    Moreover, road transport, which accounts for 4.6% of total emissions, has shown a continual decrease in VOCs emissions due to an increase in the number of recent cars being registered and improvements in emissions factors.Emissions from this category also decreased 6.7% (3,323 metric tons) in 2015 compared to the previous year, which was due to a 10.5% decrease (2014: 13.624 billion km → 2015: 12.195 billion km) in the VKT of small passenger cars.

NH 3 Emissions
As Fig. 10 and Table 12 show, there was an overall increasing trend in NH 3 emissions in 2015 compared to 2011, with a 4,666 metric ton increase in 2015 over the previous year.Agriculture (fertilizer use, livestock excrement, etc.), which is the main source of NH 3 emissions, accounts for 77.8% of total NH 3 emissions as of 2015, and emissions from this category increased 3,310 metric tons (1.5%) in 2015 compared to the previous year.There was an increase of 3,581 metric tons (1.7%) in emissions from excrement management, which influenced the increase in total emissions from this category.This was the result of a 5.6% increase (2014: 179.390 million animals → 2015: 189.417 million animals) in the number of livestock.In the industrial processes cat-egory, there was an increase of 3.7% (1,389 metric tons) in 2015 compared to the previous year; this was the result of a 4.5% increase (2014: 144.309 million kL → 2015: 150.862 million kL) in the crude oil input volume in the petroleum product manufacturing sector.
On the other hand, NH 3 emissions from the manufacturing industry category showed a 12.5% decrease (90 metric tons) compared to the previous year.This decrease was due to a 31.9%decrease (2014: 4.694507 billion m 3 → 2015: 3.196508 billion m 3 ) in LNG usage in the  (units: metric tons/year) "Other" subcategory of combustion (manufacturing industry) compared to the previous year.

CONCLUSION
Using CAPSS to estimate national emissions in 2015, we found that CO emissions were 792,776 metric tons.The major CO emission sources were road transport (31.0%), biomass burning (29.3%), and non-road transport (17.1%).NO x emissions were 1,157,728 metric tons, of which the main sources were road transport (31.9%), non-road transport (26.3%), and the manufacturing industry (14.6%).SO x emissions were 352,292 metric tons, of which the main sources were industrial processes (29.9%), energy production (25.9%), and the manufacturing industry (24.2%).TSP emissions were 604,243 metric tons, of which the main sources were fugitive dust (67.6%) and the manufacturing industry (20.1%).PM 10 emissions were 233,177 metric tons, of which the main sources were fugitive dust (47.0%) and the manufacturing industry (30.4%).PM 2.5 emissions were 98,806 metric tons, of which the main sources were the manufacturing industry (36.8%), fugitive dust (17.5%), and non-road transport (14.3%).BC emissions were 15,934 metric tons, of which the main sources were road transport (42.0%) and non-road transport (39.6%).VOCs emissions were 1,010,771 metric tons, of which the main sources were solvent use (54.9%) and industrial processes (18.1%).NH 3 emissions were 297,167 metric tons, of which the main sources were agriculture (77.8%) and industrial processes (13.3%).
Most substances showed increased emissions in 2015 relative to 2014.The percentage increases were 1.9% for NO x , 2.6% for SO x , 5.4% for TSP, 10.4% for PM 10 , 8.0.% for PM 2.5 , 0.9% for BC, 1.9% for VOCs, and 1.6% for NH 3 .Meanwhile, CO emissions decreased by 4.1%.When calculating emissions in 2015, since no improvements were made to the methodology, such as improving the emissions factors and the application method of activity levels, the increase in substances was mostly due to the increase in activity levels.In particular, the overall increase in emissions was caused by higher activity levels in sources of emissions significantly impacted by the economic situation, including construction, shipping, production processes, and manufacturing sectors.However, as the ratio of new cars to CO increased, emissions decreased continuously.
These estimates can be used in research, air quality forecast modeling, and as data to support the establishment, implementation, and assessment of air qualityrelated policies.Thus, continued research is required in order to obtain accurate data about air pollutant emission sources, to perform quantitative assessments following the establishment and implementation of related measures, and to correct the uncertainty and increase the reliability of national air pollutant emissions data.

Fig. 2 .
Fig. 2. Trends in CO emissions, by emission source, in the last 5 years.

Fig. 3 .
Fig. 3. Trends in NO x emissions, by emission source, in the last 5 years.

Fig. 4 .
Fig. 4. Trends in SO x emissions, by emission source, in the last 5 years.

Fig. 5 .
Fig. 5. Trends in TSP emissions, by emission source, in the last 5 years.

Fig. 6 .
Fig. 6.Trends in PM 10 emissions, by emission source, in the last 5 years.

Fig. 10 .
Fig. 10.Trends in NH 3 emissions, by emission source, in the last 5 years.

Table 1 .
2015 emissions and the relative contribution of air pollutants per major emission source category.(units: metric tons/year) *BC: BC(Black Carbon) as EC(Elemental Carbon)

Table 2 .
Trends in CO emissions, by emission source, in the last 5 years.

Table 3 .
Trends in NO x emissions, by emission source, in the last 5 years.

Table 4 .
Annual sulfur content of major fuel types.
*Source: Korea Petroleum Quality & Distribution Authority, sulfur content for each fuel type(units: wt%)

Table 5 .
Trends in SO x emissions, by emission source, in the last 5 years.

Table 6 .
The number of registered construction machines.(units: number of machines) *Source: Statistics on the state of construction machines, Ministry of Land, Infrastructure, and Transport

Table 7 .
Trends in TSP emissions, by emission source, in the last 5 years.

Table 8 .
Trends in PM 10 emissions, by emission source, in the last 5 years.

Table 9 .
Trends in PM 2.5 emissions, by emission source, in the last 5 years.

Table 10 .
Trends in BC emissions, by emission source, in the last 2 years.

Table 11 .
Trends in VOCs emissions, by emission source, in the last 5 years.

Table 12 .
Trends in NH 3 emissions, by emission source, in the last 5 years.