*1.1. Background*

In recent years, South Korea has been suffering from deteriorating air quality because of high particulate matter (PM) levels. In capital Seoul, PM2.5 (PM of 2.5 μm or less in diameter) concentration is nearly two times higher than what is prescribed by the World Health Organization (WHO) guidelines [1]. According to WHO, PM2.5 exposure leads to an increase in mortality because of respiratory and cardiovascular diseases [2]. In Korea, a total of 11,924 deaths were attributable to PM2.5 in 2015 [3].

PM2.5 can be directly emitted from human activities such as power plants, business facilities, and internal combustion engine vehicles (ICEVs). PM2.5 can also be produced secondarily by photochemical reaction with PM2.5 precursor species of nitrogen oxides (NOx), sulfur oxides (SOx), ammonia (NH3), and volatile organic carbons (VOC) in the atmosphere [4]. Regarding sources of domestic PM2.5 emissions, of all PM2.5 in the atmosphere in Korea, half of it comes from secondary formation. Business facilities are the largest PM2.5 emitters nationwide while diesel vehicles are the largest emitters in the Seoul metropolitan area (Seoul, Incheon, and Gyeonggi), where almost half the Korean population resides [5,6].

The Korean government has set up a series of countermeasures to control PM2.5 emissions including a Comprehensive Plan on Fine Dust Management (CPFDM). CPFDM is a comprehensive plan for cutting PM2.5 between 2020 and 2024 which aims to decrease the annual average PM2.5 concentration by 35% below the 2016 levels (26 μg/m3) by 2024. Also, domestic emission reduction target per year with reduction rate for PM2.5 (noted in the parenthesis) was set at 3300 tonnes (8%) for the industry sector; 2000 tonnes (63%) for the power generation sector; 8600 tonnes (35%) for the transportation sector; and 5200 tonnes (17%) for everyday surroundings such as road-cleaning, illegal incineration, and introduction of domestic low-NOx boilers (the term of "everyday surroundgins" is used in the official document) [7]. That is, the transportation sector, especially the road transportation sector, has the largest reduction target of PM2.5 emissions, although the power sector is facing a stricter emission reduction target in terms of the reduction rate. The road transportation sector accounted for around 70% of the total PM2.5 emissions from both road and non-road transportation sectors including fugitive road dust (FRD) in 2016. FRD is generated by tire wear, brake wear, and road wear. It is one of the major emitters accounting for 7% of the overall local emissions of PM2.5 in 2016. At that time, emissions from the road transportation sector were 11% [8].

Zero-emission vehicles (ZEVs) such as electric battery vehicles (BEVs) and fuel cell electric vehicles (FCEVs), are globally promoted for improving air quality and reducing oil consumption [9]. In Korea, ZEVs have been strongly promoted as one of PM2.5 mitigation measures for the transportation sector. In 2018, the government spent \$757 million to carry forward PM2.5 mitigation measures for the transportation sector, which accounted for 56% of the total budget for domestic PM2.5 mitigation measures. In particular, budget spending on the subsidizing ZEVs' purchase accounted for 71% of the PM2.5 mitigation budget for the transportation sector [10].

In addition to the ZEV purchase subsidy, the government also offers tax incentives (for example, tax breaks for special consumption tax, educational tax, acquisition tax, and automobile tax) for ZEVs' buyers [7], and mandates automakers to supply a certain percentage of ZEVs including low-emission vehicles (hybrid electric vehicles (HEVs) and plug in HEVs) without any incentive. Instead, the amount of mandatory supply can be deducted if automakers invest in charging station installations as a contribution to infrastructure construction [11]. Unlike automakers, owners of apartment houses, business facilities, and large car parks get a subsidy for charging station installations [12].
