Environmental Pollution 273 (2021) 116428 Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol Sensitivity of fine particulate matter concentrations in South Korea to regional ammonia emissions in Northeast Asia* * Eunhye Kim a, Byeong-Uk Kim b, Hyun Cheol Kim c, d, Soontae Kim a, a Department of Environmental & Safety Engineering, Ajou University, Suwon, South Korea b Georgia Environmental Protection Division, Atlanta, GA, 30354, USA c Air Resources Laboratory, National Oceanic and Atmospheric Administration, College Park, MD, 20740, USA d Cooperative Institute for Satellite Earth System Studies, University of Maryland, College Park, MD, 20740, USA article info abstract Article history: Ammonia (NH3) is an important precursor for forming PM2.5. In this study, we estimated the impact of Received 16 November 2020 upwind transboundary and local downwind NH3 emissions on PM2.5 and its inorganic components via Accepted 2 January 2021 photochemical grid model simulations. Nine sensitivity scenarios with ±50% perturbations of upwind Available online 5 January 2021 (China) and/or downwind (South Korea) NH3 emissions were simulated for the year 2016 over Northeast Asia. The annual mean PM2.5 concentrations in the downwind area were predicted to change from À3.3 Keywords: 3 (À18%) to 2.4 mg=m (13%) when the NH3 emissions in the upwind and downwind areas were perturbed Particulate matter by -50% to þ50%. The change in PM concentrations in the downwind area depending on the change in Long-range transport 2.5 Ammonia NH3 emissions in the upwind area was the highest in spring, followed by winter. This was mainly - Sensitivity attributed to the change in nitrate (NO3), a secondary inorganic aerosol (SIA) that is a predominant Vertical mixing constituent of PM2.5. Since NH3 is mainly emitted near the surface and vertical mixing is limited during - the night, it was modeled that the aloft nitric acid (HNO3)-to-NO3 conversion in the morning hours was increased when the NH3 accumulated near the surface during nighttime begins to mix up within the Planetary Boundary Layer (PBL) as it develops after sunrise. This implies that the control of upwind and/ or downwind NH3 emissions is effective at reducing PM2.5 concentrations in the downwind area even under NH3 rich conditions in Northeast Asia. © 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction 2019; Sun et al., 2018; Zheng et al., 2018). However, advanced emission controls, such as flue gas desulfurization (FGD), will likely In many countries, emission control policies have been imple- be required to further reduce SO2 emissions in the future, and these mented to reduce PM2.5 (particulate matter with an aerodynamic advanced emission controls can result in significant increases in diameter smaller than 2.5 mm) due to its adverse effect on public capital and operating costs for businesses (Zhang et al., 2017). health. In Northeast Asia, known for frequent events of high PM2.5 Some studies have reported that the management of ammonia concentration, policies for reducing PM2.5 have been focused on the (NH3) emissions could be cost-effective for reducing SIA concen- reduction of sulfur dioxide (SO2) and nitrogen oxides (NOx; pre- trations (Gu et al., 2014; Pinder et al., 2007), although they focused cursors of secondary inorganic aerosols (SIAs)) emissions because on estimating the impact of NH3 emission reductions on local PM2.5 the fraction of SIAs is large during high PM2.5 events (Bae et al., concentrations (Supplementary Table 1 and references therein). 2019; Huang et al., 2014; Itahashi et al., 2017; Kim et al., 2017a; Considering the lifetime and long-range transportation of PM2.5 Zhang et al., 2012). Until recently, tangible achievements as a result and its precursors (Itahashi et al., 2017; Pinder et al., 2008; Seinfeld of these policies have been reported; for example, Chinese SO2 and Pandis, 2006), changes in NH3 emissions in upwind areas could emissions decreased by 62% between 2010 and 2017 (Lachatre et al., affect concentrations of air pollutants in downwind areas. Once released into the atmosphere, NH3 can be converted into ammo- þ nium (NH4 ) depending on the atmospheric conditions, e.g. tem- perature, relative humidity, atmospheric pressure, and availability * This paper has been recommended for acceptance by Pavlos Kassomenos. of other chemicals (Seinfeld and Pandis, 2006). Thus, to estimate * Corresponding author. E-mail address: [email protected] (S. Kim). the effects of upwind NH3 changes on downwind air quality, it is https://doi.org/10.1016/j.envpol.2021.116428 0269-7491/© 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/ ). E. Kim, B.-U. Kim, H.C. Kim et al. Environmental Pollution 273 (2021) 116428 Table 1 limited due to the sparsity of the observation sites (one site located Upwind and downwind NH3 emission scenarios. in China, three located in South Korea, and 12 located in Japan). Case Upwind (China) Downwind (South Korea) More details about EANET observations can be found in EANET C50K50 50% 50% reports (EANET, 2016b). C50 50% 100% C50K150 50% 150% 2.2. Study area and period Base 100% 100% K50 100% 50% Air pollutants can be transported over long distances by west- K150 100% 150% C150K50 150% 50% erly winds in Northeast Asia (Itahashi et al., 2017; Li et al., 2007), C150 150% 100% thus China was set as the upwind area and South Korea as the C150K150 150% 150% downwind area. To examine the impact of NH3 emission changes in The simulation period is 1 year (2016). the upwind and downwind areas on PM2.5 concentrations, the study area covers Northeast Asia (Fig. 1). Specifically, the focus of this study was on the changes in PM2.5 and SIA concentrations at necessary to understand the fate of atmospheric NHx the two supersites, BR and SD, in South Korea. The Seoul Metro- þ (¼NH3 þ NH4 ) during the long-range transport in lieu of NH3 politan Area (SMA) represented by SD is a densely populated region (Gilliland et al., 2006). Surface measurements, satellite observa- with large local emissions. The Chinese contribution to PM2.5 tions, and air quality model simulation can be used to understand concentrations in the SMA has been reported to account for the fate of NHx. A challenge is that current surface observation data 30e70% (Choi et al., 2019; Kim et al., 2017b), which suggests that for Northeast Asia are available only for very limited spatiotem- the impact of NH3 emission changes in China and South Korea on poral coverage of ambient concentrations and deposition with no PM2.5 concentration could be interwoven at SD. On the other hand, vertical distribution information. Space- and airborne measure- BR is located on a small island (~51 km2) at westernmost South ments can be used to estimate NH3 vertical distribution, but they Korea approximately 200 km east of the Shandong Peninsula, exhibit low spatial and temporal resolution over limited spatial and China, that has low local emissions of PM2.5 and its precursors and temporal coverage. On the other hand, a three-dimensional is in the pathway of air pollutant transport from China to South photochemical transport model covering a wide range of time Korea throughout the year. For this reason, BR is suitable for and space can be used to explain the emission, transport, and examining the transported PM2.5 and its precursors from China to transformation of NHx. Nevertheless, results from modeling often South Korea (Jo et al., 2020). The study period was set to the year fi have high uncertainty due to dif culties in acquiring accurate NH3 2016, and monthly variations of PM2.5 and its constituents were emission data (Gilliland et al., 2006; Pinder et al., 2008)in analyzed to consider seasonal variability of synoptic meteorology conjunction with insufficient data to verify them. Thus, it is often and emissions in Northeast Asia. indispensable to conduct a series of simulations to address un- certainties in the model inputs, such as emissions. 2.3. Air quality simulation In this study, we attempted to investigate the impact of regional NH3 emissions on downwind PM2.5 concentrations in Northeast For the air quality simulation, a Eulerian photochemical model, Asia using air quality simulations with all available observational Community Multi-scale Air Quality (CMAQ) v4.7.1 was used with a data. First, we compared the observed and simulated NH3, SIA, and 27-km horizontal resolution over the study area. Furthermore, PM2.5 levels to evaluate the model performance. Second, we Process Analysis (PA), which is a probing tool provided by CMAQ, examined the sensitivity of the downwind PM2.5 concentration to was applied for comprehensive understanding: it enables quanti- both upwind and downwind NH3 emissions by using a set of sim- tative evaluation of the physical and chemical processes of air ulations. Third, we analyzed the modeled vertical profiles of NH3 pollutants (Gipson, 1999; Liu et al., 2010). The processes are þ and NH4 to explain how the upwind NH3 emission controls can calculated by applying several terms, such as emissions, advection, affect downwind areas. Last, we evaluated the effectiveness of diffusion, aerosols, chemistry, clouds, deposition, etc. (Gipson, future NH3 emission controls on PM2.5 improvements in downwind 1999). areas in terms of NH3 emission uncertainty. Meteorological input data for CMAQ were prepared by pro- cessing the output from the Weather Research and Forecasting 2. Research methods (WRF; Skamarock et al., 2008) v3.5.1 simulation using initial/ boundary conditions from the Final Operational Global Analysis 2.1.