scholarly journals Meteorology influencing springtime air quality, pollution transport, and visibility in Korea

Elem Sci Anth ◽  
2019 ◽  
Vol 7 ◽  
Author(s):  
David A. Peterson ◽  
Edward J. Hyer ◽  
Sang-Ok Han ◽  
James H. Crawford ◽  
Rokjin J. Park ◽  
...  
Keyword(s):  
Air Quality ◽  
Sea Breeze ◽  
Ozone Pollution ◽  
Pollution Transport ◽  
Sources Of Pollution ◽  
Seoul Metropolitan Area ◽  
Primary Mechanism ◽  
Range Transport ◽  
Dynamic Meteorology ◽  
The Impact

In an environment with many local, remote, persistent, and episodic sources of pollution, meteorology is the primary factor that drives periods of unhealthy air quality and reduced visibility. The 2016 Korea-United States Air Quality (KORUS-AQ) field study provides a unique opportunity to examine the impact of meteorology on the relative influence of local and transboundary pollution. Much of the KORUS-AQ campaign can be grouped into four distinct research periods based on observed synoptic meteorology, including a period of complex aerosol vertical profiles driven by dynamic meteorology, stagnation under a persistent anticyclone, low-level transport and haze development, and a blocking pattern. These episodes are examined using a diverse archive of ground, airborne, and satellite data. While frontal boundaries are recognized as the primary mechanism driving pollution transport in eastern Asia, results show that they are not always related to sustained periods of hazardous air quality and reduced visibility at the surface. Significant long-range transport of pollution and dust was constrained to a few short events, suggesting that the majority of pollutants sampled during KORUS-AQ originated from local sources. A severe regional pollution episode is examined in detail, featuring dense haze and significant secondary particle formation within a shallow moist boundary layer. Observations during KORUS-AQ also highlight a rapid, 40 ppbv increase in ozone pollution as a strong sea breeze front traversed the Seoul Metropolitan Area. Representativeness of meteorology and pollution conditions measured by KORUS-AQ is considered by comparison with climatology. This analysis is an essential step toward improved local and regional forecasting of air quality and visibility.

scholarly journals Impacts of future land use and land cover change on mid-21<sup>st</sup>-century surface ozone air quality: Distinguishing between the biogeophysical and biogeochemical effects

2019 ◽  
Author(s):  
Lang Wang ◽  
Amos P. K. Tai ◽  
Chi-Yung Tam ◽  
Mehliyar Sadiq ◽  
Peng Wang ◽  
...  
Keyword(s):  
Land Use ◽  
Air Quality ◽  
Land Cover ◽  
Dry Deposition ◽  
Surface Ozone ◽  
Boreal Summer ◽  
Ozone Pollution ◽  
Lulc Change ◽  
Lulc Changes ◽  
The Impact

Abstract. Surface ozone (O3) is an important air pollutant and greenhouse gas. Land use and land cover (LULC) is one of the critical factors influencing ozone, in addition to anthropogenic emissions and climate. LULC change can on the one hand affect ozone biogeochemically, i.e., via dry deposition and biogenic emissions of volatile organic compounds (VOCs). LULC change can on the other hand alter regional- to large-scale climate through modifying albedo and evapotranspiration, which can lead to changes in surface temperature, hydrometeorology and atmospheric circulation that can ultimately impact ozone biogeophysically over local and remote areas. Such biogeophysical effects of LULC on ozone are largely understudied. This study investigates the individual and combined biogeophysical and biogeochemical effects of LULC on ozone, and explicitly examines the critical pathway for how LULC change impacts ozone pollution. A global coupled atmosphere–chemistry–land model is driven by projected LULC changes from the present day (2000) to future (2050) under RCP4.5 and RCP8.5 scenarios, focusing on the boreal summer. Results reveal that when considering biogeochemical effects only, surface ozone is predicted to have slight changes by up to 2 ppbv maximum in some areas due to LULC changes. It is primarily driven by changes in isoprene emission and dry deposition counteracting each other in shaping ozone. In contrast, when considering the integrated effect of LULC, ozone is more substantially altered by up to 6 ppbv over several regions, reflecting the importance of biogeophysical effects on ozone changes. Furthermore, large areas of these ozone changes are found over the regions without LULC changes where the biogeophysical effect is the only pathway for such changes. The mechanism is likely that LULC change induces a regional circulation response, in particular the formation of anomalous stationary high-pressure systems, shifting of moisture transport, and near-surface warming over the middle-to-high northern latitudes in boreal summer, owing to associated changes in albedo and surface energy budget. Such temperature changes then alter ozone substantially. We conclude that the biogeophysical effect of LULC is an important pathway for the influence of LULC change on ozone air quality over both local and remote regions, even in locations without significant LULC changes. Overlooking the impact of biogeophysical effect may cause evident underestimation of the impacts of LULC change on ozone pollution.

scholarly journals Monitoring the Impact of Air Quality on the COVID-19 Fatalities in Delhi, India: Using Machine Learning Techniques

2020 ◽  
pp. 1-8
Author(s):  
Jasleen Kaur Sethi ◽  
Mamta Mittal
Keyword(s):  
Machine Learning ◽  
Air Quality ◽  
Air Pollutants ◽  
Machine Learning Techniques ◽  
Environmental Restoration ◽  
The Novel ◽  
Ozone Pollution ◽  
Learning Techniques ◽  
Novel Coronavirus ◽  
The Impact

ABSTRACT Objective: The focus of this study is to monitor the effect of lockdown on the various air pollutants due to the coronavirus disease (COVID-19) pandemic and identify the ones that affect COVID-19 fatalities so that measures to control the pollution could be enforced. Methods: Various machine learning techniques: Decision Trees, Linear Regression, and Random Forest have been applied to correlate air pollutants and COVID-19 fatalities in Delhi. Furthermore, a comparison between the concentration of various air pollutants and the air quality index during the lockdown period and last two years, 2018 and 2019, has been presented. Results: From the experimental work, it has been observed that the pollutants ozone and toluene have increased during the lockdown period. It has also been deduced that the pollutants that may impact the mortalities due to COVID-19 are ozone, NH3, NO2, and PM10. Conclusions: The novel coronavirus has led to environmental restoration due to lockdown. However, there is a need to impose measures to control ozone pollution, as there has been a significant increase in its concentration and it also impacts the COVID-19 mortality rate.

scholarly journals Long-Range Transport Influence on Key Chemical Components of PM2.5 in the Seoul Metropolitan Area, South Korea, during the Years 2012–2016

Atmosphere ◽  
2019 ◽  
Vol 11 (1) ◽  
pp. 48 ◽  
Author(s):  
Changhan Bae ◽  
Byeong-Uk Kim ◽  
Hyun Cheol Kim ◽  
Chul Yoo ◽  
Soontae Kim
Keyword(s):  
Long Range ◽  
Metropolitan Area ◽  
Inorganic Ions ◽  
Long Range Transport ◽  
Chemical Components ◽  
Component Ratio ◽  
Seoul Metropolitan Area ◽  
Range Transport ◽  
The Impact ◽  
Pm2.5 Concentration

This study identified the key chemical components based on an analysis of the seasonal variations of ground level PM2.5 concentrations and its major chemical constituents (sulfate, nitrate, ammonium, organic carbon, and elemental carbon) in the Seoul Metropolitan Area (SMA), over a period of five years, ranging from 2012 to 2016. It was found that the mean PM2.5 concentration in the SMA was 33.7 μg/m3, while inorganic ions accounted for 53% of the total mass concentration. The component ratio of inorganic ions increased by up to 61%–63% as the daily mean PM2.5 concentration increased. In spring, nitrate was the dominant component of PM2.5, accounting for 17%–32% of the monthly mean PM2.5 concentrations. In order to quantify the impact of long-range transport on the SMA PM2.5, a set of sensitivity simulations with the community multiscale air-quality model was performed. Results show that the annual averaged impact of Chinese emissions on SMA PM2.5 concentrations ranged from 41% to 44% during the five years. Chinese emissions’ impact on SMA nitrate ranged from 50% (winter) to 67% (spring). This result exhibits that reductions in SO2 and NOX emissions are crucial to alleviate the PM2.5 concentration. It is expected that NOX emission reduction efforts in China will help decrease PM2.5 concentrations in the SMA.

scholarly journals Regional contributions to particulate matter concentration in the Seoul metropolitan area, South Korea: seasonal variation and sensitivity to meteorology and emissions inventory

2017 ◽  
Vol 17 (17) ◽  
pp. 10315-10332 ◽  
Author(s):  
Hyun Cheol Kim ◽  
Eunhye Kim ◽  
Changhan Bae ◽  
Jeong Hoon Cho ◽  
Byeong-Uk Kim ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Seasonal Variation ◽  
Air Quality ◽  
South Korea ◽  
Metropolitan Area ◽  
Policy Support ◽  
Seoul Metropolitan Area ◽  
Regional Air Quality ◽  
Emissions Inventories ◽  
The Impact

Abstract. The impact of regional emissions (e.g., domestic and international) on surface particulate matter (PM) concentrations in the Seoul metropolitan area (SMA), South Korea, and its sensitivities to meteorology and emissions inventories are quantitatively estimated for 2014 using regional air quality modeling systems. Located on the downwind side of strong sources of anthropogenic emissions, South Korea bears the full impact of the regional transport of pollutants and their precursors. However, the impact of foreign emissions sources has not yet been fully documented. We utilized two regional air quality simulation systems: (1) a Weather Research and Forecasting and Community Multi-Scale Air Quality (CMAQ) system and (2) a United Kingdom Met Office Unified Model and CMAQ system. The following combinations of emissions inventories are used: the Intercontinental Chemical Transport Experiment-Phase B, the Inter-comparison Study for Asia 2010, and the National Institute of Environment Research Clean Air Policy Support System. Partial contributions of domestic and foreign emissions are estimated using a brute force approach, adjusting South Korean emissions to 50 %. Results show that foreign emissions contributed  ∼  60 % of SMA surface PM concentration in 2014. Estimated contributions display clear seasonal variation, with foreign emissions having a higher impact during the cold season (fall to spring), reaching  ∼  70 % in March, and making lower contributions in the summer,  ∼  45 % in September. We also found that simulated surface PM concentration is sensitive to meteorology, but estimated contributions are mostly consistent. Regional contributions are also found to be sensitive to the choice of emissions inventories.

Effect of sea breeze regime on aerosol optical properties over the city of Rome, Italy.

2020 ◽  
Author(s):  
Annalisa Di Bernardino ◽  
Anna Maria Iannarelli ◽  
Stefano Casadio ◽  
Gabriele Mevi ◽  
Monica Campanelli ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Optical Properties ◽  
Air Quality ◽  
Sea Breeze ◽  
Coastal Areas ◽  
Horizontal Wind ◽  
Tyrrhenian Sea ◽  
Depth Analysis ◽  
The Impact ◽  
The City

&lt;p&gt;Mesoscale meteorological phenomena, such as sea-land breeze regime, strongly impact meteorological conditions of coastal areas, affecting wind intensity, moisture, heat and momentum fluxes and polluted air masses dispersion. This effect must be considered in order to correct design urban spaces, predict the possible influence of land use change on air pollution and climate change and, consequently, improve the quality of life and urban comfort.&lt;/p&gt;&lt;p&gt;In recent years, it has been shown that the breeze regime does not only affect microclimatic conditions but also air quality in coastal areas, because of the mixing of different types of aerosols and condensable gases. Moreover, the advection of marine, colder and more humid air leads to the decrease of the boundary layer height and, consequently, to the increase of the surface concentration of locally emitted pollutants, that are trapped within the boundary layer itself.&lt;/p&gt;&lt;p&gt;The effect of breeze regime is particularly interesting in coastal cities, where the sea breeze entails large modification of physical, optical, chemical, and hygroscopic properties of the urban aerosol.&lt;/p&gt;&lt;p&gt;In this work, we developed an approach to determine the breeze effect on aerosol in correspondence of the BAQUNIN [1] Super-site urban location, in the centre of Rome, Italy. The city is about 28 km far from the Tyrrhenian coast and is often exposed to sea-breeze circulation and to extreme aerosol events [2] [3].&lt;/p&gt;&lt;p&gt;In-situ measurements obtained from different remote sensing instruments are used: (i) vertical profile of horizontal wind velocity and direction by means of SODAR wind profiler; (ii) moisture, air temperature and wind speed from ground-based meteorological station; (iii) aerosol optical depth (AOD), height and evolution of the Boundary Layer from Raman and elastic LIDAR; (iv) precipitable water, AOD, &amp;#197;ngstr&amp;#246;m exponent (AE) and single-scattering albedo (SSA) from sun-photometer CIMEL [4], (v) AOD, AE and SSA from POM 01 L Prede sun-sky radiometer [5][6], (vi) superficial NO&lt;sub&gt;2&lt;/sub&gt; and formaldehyde amounts from PANDORA spectrometer [7], (vii) particulate matter (PM&lt;sub&gt;2.5 &lt;/sub&gt;and PM&lt;sub&gt;10&lt;/sub&gt;) concentrations from ground-based air quality station.&lt;/p&gt;&lt;p&gt;The investigation is focused on several days, during summer of 2019, characterized by anemological breeze regime conditions.&lt;/p&gt;&lt;p&gt;In this study, we present preliminary results aimed to the in-depth analysis of the effects of the breeze regime on the optical properties of aerosols in coastal, urban environment and the impact of the aerosol vertical stratification on ground-level PM concentrations.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;[1] BAQUNIN Boundary-layer Air Quality-analysis Using Network of Instruments, www.baqunin.eu&lt;/p&gt;&lt;p&gt;[2] Petenko I. et al. (2011) &amp;#8220;Local circulation diurnal patterns and their relationship with large-scale flows in a coastal area of the Tyrrhenian sea&amp;#8221;, Boundary-Layer Meteorology, 139:353-366.&lt;/p&gt;&lt;p&gt;[3] Ciardini V. et al. (2012) &amp;#8220;Seasonal variability of tropospheric aerosols in Rome&amp;#8221;, Atmospheric Research, 118:205-214.&lt;/p&gt;&lt;p&gt;[4] AERONET, https://aeronet.gsfc.nasa.gov/new_web/index.html&lt;/p&gt;&lt;p&gt;[5] EUROSKYRAD http://www.euroskyrad.net/&lt;/p&gt;&lt;p&gt;[6] Campanelli M. et al. (2019) &amp;#8220;Aerosol optical characteristics in the urban area of Rome, Italy, and their impact on the UV index&amp;#8221;, Atmospheric Measurement Techniques Discussion.&lt;/p&gt;&lt;p&gt;[7] PGN, https://www.pandonia-global-network.org/&lt;/p&gt;

scholarly journals Megacity and local contributions to regional air pollution: An aircraft case study over London

2019 ◽  
Author(s):  
Kirsti Ashworth ◽  
Silvia Bucci ◽  
Peter J. Gallimore ◽  
Junghwa Lee ◽  
Beth S. Nelson ◽  
...  
Keyword(s):  
Air Quality ◽  
Early Career ◽  
Atmospheric Measurements ◽  
Airborne Measurements ◽  
Sources Of Pollution ◽  
Pollutant Concentrations ◽  
Local Sources ◽  
The Uk ◽  
The Impact ◽  
Pollution Events

Abstract. In July 2017 three research flights circumnavigating the megacity of London were conducted as a part of the STANCO training school for students and early career researchers organised by EUFAR (European Facility for Aircraft Research). Measurements were made from the UK’s Facility for Airborne Atmospheric Measurements (FAAM) BAe-146-301 Atmospheric Research Aircraft with the aim to sample, characterise and quantify the impact of megacity outflow pollution on air quality in the surrounding region. Conditions were extremely favourable for airborne measurements and all three flights were able to observe clear pollution events along the flight path. A small change in wind direction provided sufficiently different airmass origins over the two days such that a distinct pollution plume from London, attributable marine emissions and a double-peaked dispersed area of pollution resulting from a combination of local and transported emissions were measured. We were able to analyse the effect of London emissions on air quality in the wider region and the extent to which local sources contribute to pollution events. The background air upwind of London was relatively clean during both days; concentrations of CO were 88–95 ppbv, total (measured) volatile organic compounds (VOCs) were 1.6–1.8 ppbv, and NOx were 0.7–0.8 ppbv. Downwind of London, we encountered elevations in all species with CO > 100 ppbv, VOCs 2.8–3.8 ppbv, CH4 > 2080 ppbv and NOx > 4 ppbv, and peak concentrations in individual pollution events higher still. Levels of O3 were inversely correlated with NOx during the first flight, with O3 concentrations of 37 ppbv upwind falling to ~ 26 ppbv in the well-defined London plume. Mass balance techniques were applied to estimate pollutant fluxes from London. Our calculated CO2 fluxes are within 10 % of those estimated previously, but there was a greater disparity in our estimates of CH4 and CO. On the second day, winds were lighter and downwind O3 concentrations were elevated to ~ 39–43 ppbv (from ~ 32–35 ppbv upwind), reflecting the contribution of more aged pollution to the regional background. Elevations in pollutant concentrations were dispersed over a wider area than the first day, although we also encountered a number of clear spikes from local sources. This series of flights demonstrated that megacity outflow, local fresh emissions and more distant UK sources of pollution all contribute to pollution events in the southeast of the UK. These sources must therefore all be well-characterised and constrained to understand air quality around London.

scholarly journals Impact of transatlantic transport episodes on summertime ozone in Europe

2006 ◽  
Vol 6 (8) ◽  
pp. 2057-2072 ◽  
Author(s):  
G. Guerova ◽  
I. Bey ◽  
J.-L. Attié ◽  
R. V. Martin ◽  
J. Cui ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Long Range ◽  
North American ◽  
Tropospheric Chemistry ◽  
Long Range Transport ◽  
Back Trajectory ◽  
Pollution Transport ◽  
Upper Troposphere ◽  
Range Transport ◽  
The Impact

Abstract. This paper reports on the transport of ozone (O3) and related species over the North Atlantic ocean and its impact on Europe. Measurements of nitrogen dioxide (NO2) and carbon monoxide (CO) columns from the GOME and MOPITT satellite instruments, respectively, are used in conjunction with the GEOS-CHEM global model of transport and tropospheric chemistry to identify the major events of long range transport that reach Europe over the course of summer 2000. Sensitivity model simulations are used to analyse observed O3 distributions with respect to the impact of long range transport events. For that purpose, we used in-situ O3 observations taken at the mountain site of Jungfraujoch as well as O3 vertical profiles taken in the vicinity of central European cities. Over the course of summer 2000, we identified 9 major episodes of transatlantic pollution transport; 7 events are associated with transient cyclones while 2 events occur through zonal transport (e.g. by advection in the strong low-level westerly winds established in summer between the Azores anticyclone and transient cyclones). We find that on average three episodes occur per month with the strongest ones being in June. The number and frequency of long range transport events that reach Europe are driven by the position and strength of the Azores anticyclone. Model sensitivity simulations indicate that the summer mean North American O3 contribution ranges from 3 to 5 ppb (7–11%) in the planetary boundary layer and 10 to 13 ppb (18–23%) in the middle and upper troposphere. During particular episodes, North American sources can result in O3 enhancements up to 25–28 ppb in the layer between 800–600 hPa and 10–12 ppb in the boundary layer. The impact of the zonal transport events on O3 distribution over Europe is more clearly seen below 700 hPa as they tend to transport pollution at lower levels while the events associated with transient cyclones are more likely to have an impact on the middle and upper troposphere (i.e. above 600 hPa). The air mass origins found in the GEOS-CHEM model are clearly confirmed by back trajectory analyses. During most of the 9 events, a strong contribution in North American O3 is in general associated with only little European O3 and vice-versa (in particular at the Jungfraujoch). A substantial North American contribution (e.g., 30% or higher) to O3 over Europe does not always result in pronounced O3 enhancements in the observations during our period of study.

scholarly journals Case studies of ozone transport between North America and Europe in summer 2000

2005 ◽  
Vol 5 (4) ◽  
pp. 6127-6184 ◽  
Author(s):  
G. Guerova ◽  
I. Bey ◽  
J.-L. Attié ◽  
R. V. Martin
Keyword(s):  
North America ◽  
North American ◽  
North Atlantic Ocean ◽  
Conveyor Belt ◽  
Tropospheric Chemistry ◽  
Pollution Transport ◽  
The North ◽  
Range Transport ◽  
European Mountain ◽  
The Impact

Abstract. This paper reports on Long Range Transport (LRT) of ozone and related species over the North Atlantic ocean and its impact on Europe. Measurements of NO2 and O3 columns from the GOME and MOPITT satellite instruments are first used in conjunction with the GEOS-CHEM global model of transport and tropospheric chemistry to identify the major events of LRT that reach Europe over the course of the summer 2000. Model simulations are then used to examine surface O3 observations at a European mountain site and O3 vertical profiles over several European cities to quantify the impact of the LRT events on the European ozone distributions. Over the course of summer 2000, we identified nine major episodes of pollution transport between North America and Europe, which are in majority associated with WCB/post-frontal outflow (7 events) and zonal transport (2 events). We find that on average three episodes occur per month with the strongest ones being in June. The number and frequency of LRT events that reach Europe after leaving North America is strongly driven by the position and strength of the Azores anticyclone. After leaving North America, the plumes can either i) travel in the North American cyclones, mostly in the Warm Conveyor Belt (WCB), tracking poleward and thus reach Europe at high latitudes; ii) be transported zonally between 40° and 55° N directly to Europe; iii) be incorporated into the Azores anticyclone and reach Europe at mid-latitudes. Based on model sensitivity simulation it can be concluded that on average the North American sources of ozone contribute between 2–8 ppb in PBL and 10–13 ppb in FT. During particular episodes the North American sources resulted in O3 enhancement up to 25–28 ppb in the layer between 800–600 hPa and 10–12 ppb in PBL. For some episodes a substantial North American contribution (30% or higher) does not translate into a well marked enhancement of the total O3.

scholarly journals The Impact of Uncertainties in African Biomass Burning Emission Estimates on Modeling Global Air Quality, Long Range Transport and Tropospheric Chemical Lifetimes

Atmosphere ◽  
2012 ◽  
Vol 3 (1) ◽  
pp. 132-163 ◽  
Author(s):  
Jason E. Williams ◽  
Michiel van Weele ◽  
Peter F. J. van Velthoven ◽  
Marinus P. Scheele ◽  
Catherine Liousse ◽  
...  
Keyword(s):  
Air Quality ◽  
Long Range ◽  
Biomass Burning ◽  
Long Range Transport ◽  
Range Transport ◽  
The Impact

scholarly journals Influence of Intense secondary aerosol formation and long range transport on aerosol chemistry and properties in the Seoul Metropolitan Area during spring time: Results from KORUS-AQ

2017 ◽  
Author(s):  
Hwajin Kim ◽  
Qi Zhang ◽  
Jongbae Heo
Keyword(s):  
Air Quality ◽  
Metropolitan Area ◽  
Meteorological Conditions ◽  
Photochemical Reactions ◽  
Long Range Transport ◽  
Emission Sources ◽  
Aerosol Formation ◽  
Atmospheric Processes ◽  
Seoul Metropolitan Area ◽  
Range Transport

Abstract. Non-refractory submicrometer particulate matter (NR-PM1) was measured in the Seoul Metropolitan Area (SMA), Korea, using an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) from April 14 to June 15, 2016, as a part of the Korea-U.S. Air Quality Study (KORUS-AQ) campaign. This was the first highly time-resolved, real-time measurement study of springtime aerosol in SMA and the results reveal valuable insights into the sources and atmospheric processes that contribute to PM pollution in this region. The average concentration of submicrometer aerosol (PM1 = NR-PM1 + black carbon (BC)) was 22.1 µg m−3, which was composed of 44 % organics, 20 % sulfate, 17 % nitrate, 12 % ammonium, and 7 % BC. Organics had an average atomic oxygen-to-carbon (O / C) ratio of 0.49 and an average organic mass-to-carbon (OM / OC) ratio of 1.82. The concentration and composition of PM1 varied dynamically due to the influences of different meteorological conditions, emission sources, and air mass origins. Four distinct sources of OA were identified via positive matrix factorization (PMF) analysis of the HR-ToF-AMS data: vehicle emissions represented by a hydrocarbon like OA factor (HOA; O / C = 0.15; 17 % of OA mass), cooking activities represented by a cooking OA factor (COA; O / C = 0.19; 22 % of OA mass), and secondary organic aerosol (SOA) represented by a semi-volatile oxygenated OA factor (SV-OOA; O / C = 0.44; 27 % of OA mass) and a low volatility oxygenated OA factor (LV-OOA; O / C = 0.91; 34 % of OA mass). Our results indicate that air quality in SMA during KORUS-AQ was influenced strongly by secondary aerosol formation with sulfate, nitrate, ammonium, SV-OOA, and LV-OOA together accounting for 76 % of the PM1 mass. In particular, high temperature, elevated ozone concentrations, and photochemical reactions during daytime promoted the formation of SV-OOA, LV-OOA and sulfate whereas nocturnal processing of nitrogen oxides and daytime photochemical reactions promoted nitrate formation. In addition, gas-to-particle partitioning processes appeared to have enhanced nighttime SV-OOA and nitrate formation. During a period of 4 days (from May 20 to May 23), LV-OOA was significantly enhanced and accounted for up to 41 % of the PM1 mass. This intense LV-OOA formation event was associated with large enhancements of both anthropogenic and biogenic VOCs (e.g., isoprene, toluene), high concentration of Ox (= O3 + NO2), strong solar radiation, and stagnant conditions, suggesting that it was mainly driven by local photochemical formation. We have also investigated the formation and evolution mechanisms of severe haze episodes. Unlike the winter haze events which were mainly caused by intense local emissions coupled with stagnant meteorological conditions, the spring haze events appeared to be influenced by both regional and local factors. For example, there were episodes of long range transport of plumes followed by calm meteorology conditions, which promoted the formation and accumulation of local secondary species, leading to high concentrations of PM. Overall, our results indicate that PM pollutants in urban Korea originate from complex emission sources and atmospheric processes and that the concentrations and composition of PM are controlled by various factors including meteorological conditions, local anthropogenic emissions, and upwind sources. Therefore, understanding the high aerosol pollution followed by efficient strategies to remove precursors are important to control the air pollution.

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