scholarly journals Elemental Carbon Observed at a Peri-Urban Forest Site near the Seoul Metropolitan Area as a Tracer of Seasonal Haze Occurrence

Atmosphere ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1627
Author(s):  
Jeeyoung Ham ◽  
Inseon Suh ◽  
Meehye Lee ◽  
Hyunseok Kim ◽  
Soyoung Kim
Keyword(s):  
Organic Carbon ◽  
Metropolitan Area ◽  
Elemental Carbon ◽  
Urban Forest ◽  
Biomass Combustion ◽  
Forest Site ◽  
Carbonaceous Aerosols ◽  
Study Region ◽  
Seoul Metropolitan Area ◽  
Haze Days

In order to identify the seasonal variability and source of carbonaceous aerosols in relation to haze occurrence, organic carbon (OC) and elemental carbon (EC) were continuously measured at the Taehwa Research Forest (TRF) near the Seoul metropolitan area from May 2013 to April 2014. For the entire experiment, the mean OC (5.1 µgC/m3) and EC (1.7 µgC/m3) concentrations of TRF were comparable to those of Seoul, with noticeably higher concentrations in winter and spring than in other seasons, and during haze days (6.6 ± 3.2 and 2.1 ± 1.0 μgC/m3) than during non-haze days (3.5 ± 2.2 and 1.3 ± 0.8 μgC/m3). The seasonal characteristics of OC and EC reveal the various sources of haze, including biomass combustion haze either transported for long distances or, in spring, from domestic regions, the greatest contribution of secondary organic carbon (SOC) in summer, and fossil fuel combustion in winter and fall. In addition, the seasonal OC/EC ratios between haze and non-haze days highlights that the increase in EC was more distinct than that of OC during haze episodes, thus suggesting that EC observed at a peri-urban forest site serves as a useful indicator for seasonally varying source types of haze aerosols in the study region.

scholarly journals Fossil vs. non-fossil sources of fine carbonaceous aerosols in four Chinese cities during the extreme winter haze episode of 2013

2015 ◽  
Vol 15 (3) ◽  
pp. 1299-1312 ◽  
Author(s):  
Y.-L. Zhang ◽  
R.-J. Huang ◽  
I. El Haddad ◽  
K.-F. Ho ◽  
J.-J. Cao ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Organic Carbon ◽  
Biomass Burning ◽  
Water Soluble ◽  
Total Carbon ◽  
World Health ◽  
Biomass Combustion ◽  
Carbonaceous Aerosols ◽  
Haze Episode ◽  
Mass Concentrations

Abstract. During winter 2013, extremely high concentrations (i.e., 4–20 times higher than the World Health Organization guideline) of PM2.5 (particulate matter with an aerodynamic diameter < 2.5 μm) mass concentrations (24 h samples) were found in four major cities in China including Xi'an, Beijing, Shanghai and Guangzhou. Statistical analysis of a combined data set from elemental carbon (EC), organic carbon (OC), 14C and biomass-burning marker measurements using Latin hypercube sampling allowed a quantitative source apportionment of carbonaceous aerosols. Based on 14C measurements of EC fractions (six samples each city), we found that fossil emissions from coal combustion and vehicle exhaust dominated EC with a mean contribution of 75 ± 8% across all sites. The remaining 25 ± 8% was exclusively attributed to biomass combustion, consistent with the measurements of biomass-burning markers such as anhydrosugars (levoglucosan and mannosan) and water-soluble potassium (K+). With a combination of the levoglucosan-to-mannosan and levoglucosan-to-K+ ratios, the major source of biomass burning in winter in China is suggested to be combustion of crop residues. The contribution of fossil sources to OC was highest in Beijing (58 ± 5%) and decreased from Shanghai (49 ± 2%) to Xi'an (38 ± 3%) and Guangzhou (35 ± 7%). Generally, a larger fraction of fossil OC was from secondary origins than primary sources for all sites. Non-fossil sources accounted on average for 55 ± 10 and 48 ± 9% of OC and total carbon (TC), respectively, which suggests that non-fossil emissions were very important contributors of urban carbonaceous aerosols in China. The primary biomass-burning emissions accounted for 40 ± 8, 48 ± 18, 53 ± 4 and 65 ± 26% of non-fossil OC for Xi'an, Beijing, Shanghai and Guangzhou, respectively. Other non-fossil sources excluding primary biomass burning were mainly attributed to formation of secondary organic carbon (SOC) from non-fossil precursors such as biomass-burning emissions. For each site, we also compared samples from moderately to heavily polluted days according to particulate matter mass. Despite a significant increase of the absolute mass concentrations of primary emissions from both fossil and non-fossil sources during the heavily polluted events, their relative contribution to TC was even decreased, whereas the portion of SOC was consistently increased at all sites. This observation indicates that SOC was an important fraction in the increment of carbonaceous aerosols during the haze episode in China.

scholarly journals Source apportionment of carbonaceous aerosol in southern Sweden

2011 ◽  
Vol 11 (22) ◽  
pp. 11387-11400 ◽  
Author(s):  
J. Genberg ◽  
M. Hyder ◽  
K. Stenström ◽  
R. Bergström ◽  
D. Simpson ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Source Apportionment ◽  
Fossil Fuels ◽  
Elemental Carbon ◽  
Transport Model ◽  
Total Carbon ◽  
Carbonaceous Aerosol ◽  
Anthropogenic Sources ◽  
Biomass Combustion ◽  
Southern Sweden

Abstract. A one-year study was performed at the Vavihill background station in southern Sweden to estimate the anthropogenic contribution to the carbonaceous aerosol. Weekly samples of the particulate matter PM10 were collected on quartz filters, and the amounts of organic carbon, elemental carbon, radiocarbon (14C) and levoglucosan were measured. This approach enabled source apportionment of the total carbon in the PM10 fraction using the concentration ratios of the sources. The sources considered in this study were emissions from the combustion of fossil fuels and biomass, as well as biogenic sources. During the summer, the carbonaceous aerosol mass was dominated by compounds of biogenic origin (80%), which are associated with biogenic primary and secondary organic aerosols. During the winter months, biomass combustion (32%) and fossil fuel combustion (28%) were the main contributors to the carbonaceous aerosol. Elemental carbon concentrations in winter were about twice as large as during summer, and can be attributed to biomass combustion, probably from domestic wood burning. The contribution of fossil fuels to elemental carbon was stable throughout the year, although the fossil contribution to organic carbon increased during the winter. Thus, the organic aerosol originated mainly from natural sources during the summer and from anthropogenic sources during the winter. The result of this source apportionment was compared with results from the EMEP MSC-W chemical transport model. The model and measurements were generally consistent for total atmospheric organic carbon, however, the contribution of the sources varied substantially. E.g. the biomass burning contributions of OC were underestimated by the model by a factor of 2.2 compared to the measurements.

scholarly journals Elemental and Organic Carbon, Ionic and Non ionic components in TSP and PM Particulates of Kathmandu 10 Valley, Nepal

2016 ◽  
Vol 11 (1) ◽  
pp. 79-87 ◽  
Author(s):  
R. K. Sharma ◽  
B. K. Bhattarai ◽  
B. K. Sapkota ◽  
M. B. Gewali ◽  
B. Kjeldstad ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Elemental Carbon ◽  
Ambient Air ◽  
Particulate Matters ◽  
Carbonaceous Aerosols ◽  
Vehicular Emission ◽  
Wind Pattern ◽  
X Ray ◽  
Air Sampler ◽  
Ionic Components

Particulate matters of different aerodynamic diameters; TSP, PM10 for 24 hours were collected on quartz 47mm filter paper using Frm OMNITM Ambient Air Sampler from December 2010 to March 2011 and analyzed. The analysis of these sample collected were carried out by gravimetric, X-ray fluorescent and ion-chromatographic methods. TSP value for the observed period lies between 31.3-84.08 μg/m3 while PM10 ranges from 39.5-104.2 μg/m3. Daily carbonaceous aerosols concentration in TSP varied widely between (5.3-18.2 μg/m3) for Organic carbon (OC) and 5.6-10.2 μg/m3 for Elemental carbon (EC). Similarly in PM10 the range was from 4.8-14.1 and 3.9-10.1 μg/m3 respectively. The OC/EC ratio in the particulate matters ranges from 0.9-1.4. OC/EC ratio within 1.1 infers vehicular emission as a major source of carbonaceous aerosols in the valley. Further, among the nonionic components analyzed (K, Ca, Fe, Ti and Pb ) showed highest concentration of Fe as 2.5 μg/m3 while lowest of Pb as 0.001 μg/m3.The ionic components analyzed shows presence of SO4 2- and NH4 + in most of the samples while Cl-, NO3- and Ca2+ are only in few samples. Few samples of soil analyzed shows maximum of 32 elements. Variation in the concentration of ionic nonionic and carbonaceous aerosols is not related with wind pattern and its velocity.Journal of the Institute of Engineering, 2015, 11(1): 79-87

scholarly journals Ionic and carbonaceous compositions of PM<sub>10</sub>, PM<sub>2.5</sub> and PM<sub>1.0</sub> at Gosan ABC superstation and their ratios as source signature

2011 ◽  
Vol 11 (7) ◽  
pp. 20521-20573 ◽  
Author(s):  
S. Lim ◽  
M. Lee ◽  
G. Lee ◽  
S. Kim ◽  
S. Yoon ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Motor Vehicle ◽  
Southern China ◽  
Regional Scale ◽  
East Sea ◽  
Carbonaceous Aerosols ◽  
Vehicle Exhaust ◽  
Study Region ◽  
Air Masses ◽  
Pm2.5 And Pm10

Abstract. PM1.0, PM2.5, and PM10 were sampled at Gosan ABC Superstation on Jeju Island from August 2007 to September 2008. The carbonaceous aerosols were quantified with the thermal/optical reflectance (TOR) method, which produced five organic carbon (OC) fractions, OC1, OC2, OC3, OC4, and pyrolyzed organic carbon (OP), and three elemental carbon (EC) fractions, EC1, EC2, and EC3. The mean mass concentrations of PM1.0, PM2.5, and PM10 were 13.72 μg m−3, 17.24 μg m−3, and 28.37 μg m−3, respectively. The averaged mass fractions of OC and EC were 23.0 % and 10.4 % for PM1.0, 22.9 % and 9.8 % for PM2.5, and 16.4 % and 6.0 % for PM10. Among the OC and EC sub-components, OC2 and EC2+3 were enriched in the fine mode, but OC3 and OC4 in the coarse mode. The filter-based PM1.0 EC agreed well with black carbon (BC) measured by an Aethalometer, and PM10 EC was higher than BC, implying less light absorption by larger particles. EC was well correlated with sulfate, resulting in good relationships of sulfate with both aerosol scattering coefficient measured by Nephelometer and BC concentration. Our measurements of EC confirmed the definition of EC1 as char-EC emitted from smoldering combustion and EC2+3 as soot-EC generated from higher-temperature combustion such as motor vehicle exhaust and coal combustion. In particular, EC1 was strongly correlated with potassium, a traditional biomass burning indicator, except during the summer, when the ratio of EC1 to EC2+3 was the lowest. We also found the ratios of major chemical species to be a useful tool to constrain the main sources of aerosols, by which the five air masses were well distinguished: Siberia, Beijing, Shanghai, Yellow Sea, and East Sea types. Except Siberian air, the continental background of the study region, Beijing plumes showed the highest EC1 (and OP) to sulfate ratio, which implies that this air mass had the highest net warming by aerosols of the four air masses. Shanghai-type air, which was heavily influenced by southern China, showed the highest sulfate enhancement. The highest EC2+3/EC1 ratio was found in aged East Sea air, demonstrating a significant influence of motor vehicle emissions from South Korea and Japan and less influence from industrial regions of China. The high ratio results from the longer residence time and less sensitivity to wet scavenging of EC2+3 compared to EC1, indicating that soot-EC could have greater consequence in regional-scale warming.

scholarly journals Measurement report: Characterization of severe spring haze episodes and influences of long-range transport in the Seoul metropolitan area in March 2019

2020 ◽  
Vol 20 (19) ◽  
pp. 11527-11550
Author(s):  
Hwajin Kim ◽  
Qi Zhang ◽  
Yele Sun
Keyword(s):  
Metropolitan Area ◽  
Temporal Trends ◽  
Organic Aerosols ◽  
Multiple Linear Regression Model ◽  
Early Spring ◽  
Regional Transport ◽  
Air Masses ◽  
Seoul Metropolitan Area ◽  
Local Emissions ◽  
Haze Days

Abstract. Severe haze episodes have occurred frequently in the Seoul metropolitan area (SMA) and throughout East Asian countries, especially during winter and early spring. Although notable progress has been attained in understanding these issues, the causes of severe haze formation have not yet been fully investigated. SMA haze is especially difficult to understand, because the area is impacted by both local emissions from anthropogenic and biogenic activities and emissions transported from upwind sources. Here, we investigated the emission sources and formation processes of particulate matter (PM) during three haze episodes measured in early spring of 2019, from 22 February to 2 April, using a high-resolution aerosol mass spectrometer (HR-AMS). Overall, the average concentration of nonrefractory submicron aerosol (NR-PM1) + BC (black carbon) was 35.1 µg m−3, which was composed of 38 % organics, 12 % SO4, 30 % NO3, 13 % NH4, and 5 % BC. The organics had an average oxygen-to-carbon ratio (O∕C) of 0.52 and an average organic mass to organic carbon ratio (OM∕OC) of 1.86. Seven distinct sources of organic aerosols (OAs) were identified via positive matrix factorization (PMF) analysis of the HR-AMS data: vehicle-emitted hydrocarbon-like OA (HOA), cooking OA (COA), solid-fuel-burning emitted OA (SFOA), and four different types of oxidized secondary OA with varying oxidation degrees and temporal trends. Of the 40 d of the measurement period, 23 were identified as haze days (daily average: >35 µg m−3), during which three severe haze episodes were recorded. In particular, PM1 concentration exceeded 100 µg m−3 during the first episode when an alert was issued, and strict emission controls were implemented in the SMA. Our results showed that nitrate dominated during the three haze episodes and accounted for 39 %–43 % of the PM1 concentration on average (vs. 21 %–24 % during the low-loading period), for which there were indications of regional-transport influences. Two regional-transport-influenced oxidized organic aerosols (OOAs), i.e., less oxidized OOA2 (LO-OOA2) and more oxidized OOA2 (MO-OOA2), contributed substantially to the total PM1 during the haze period (12 %–14 % vs. 7 % during the low-loading period), as well. In contrast, HOA and COA only contributed little (4 %–8 % vs. 4 %–6 % during the low-loading period) to the PM1 concentration during the haze days, indicating that local emissions were likely not the main reason for the severe haze issues. Hence, from simultaneous downwind (SMA) and upwind (Beijing) measurements using HR-AMS and ACSM (aerosol chemical speciation monitor) over the same period, the temporal variations in PM1 and each chemical species showed peak values on the order of Beijing (upwind) to the SMA for approximately 2 d. Furthermore, lead (Pb) derived from HR-AMS measurements was observed to increase significantly during the haze period and showed good correlations with MO-OOA2 and LO-OOA2, which is consistent with regional sources. A multiple linear regression model indicated that the transported regionally processed air masses contributed significantly to Pb in the SMA (31 %), especially during the haze period, although local burning was also important by contributing 38 %. The above results suggest that regional transport of polluted air masses might have played an important role in the formation of the haze episodes in the SMA during early spring.

scholarly journals Source apportionment of carbonaceous aerosol in southern Sweden

2011 ◽  
Vol 11 (5) ◽  
pp. 13575-13616 ◽  
Author(s):  
J. Genberg ◽  
M. Hyder ◽  
K. Stenström ◽  
R. Bergström ◽  
D. Simpson ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Source Apportionment ◽  
Fossil Fuels ◽  
Elemental Carbon ◽  
Total Carbon ◽  
Carbonaceous Aerosol ◽  
Anthropogenic Sources ◽  
Biomass Combustion ◽  
Southern Sweden ◽  
One Year

Abstract. A one-year study was performed at the Vavihill background station in southern Sweden to estimate the anthropogenic contribution to the carbonaceous aerosol. Weekly samples of the particulate matter PM10 were collected on quartz filters, and the amounts of organic carbon, elemental carbon, radiocarbon (14C) and levoglucosan were measured. This approach enabled source apportionment of the total carbon in the PM10 fraction using the concentration ratios of the sources. The sources considered in this study were emissions from the combustion of fossil fuels and biomass, as well as biogenic sources. During the summer, the carbonaceous aerosol mass was dominated by compounds of biogenic origin (82 %), which are associated with biogenic primary and secondary organic aerosols. During the winter months, biomass combustion (38 %) and fossil fuel combustion (33 %) were the main contributors to the carbonaceous aerosol. Elemental carbon concentrations in winter were about twice as large as during summer, and can be attributed to biomass combustion, probably from domestic wood burning. The contribution of fossil fuels to elemental carbon was stable throughout the year, although the fossil contribution to organic carbon increased during the winter. Thus, the organic aerosol originated mainly from natural sources during the summer and from anthropogenic sources during the winter. The result of this source apportionment was compared with results from the EMEP model. The model and measurements were generally consistent for total atmospheric organic carbon, however, the contribution of the sources varied substantially. E.g. the biomass burning contributions of OC were underestimated by the model by a factor of 8.2 compared to the measurements.

13C signatures of aerosol organic and elemental carbon from major combustion sources in China and worldwide

2021 ◽  
Author(s):  
Peng Yao ◽  
Haiyan Ni ◽  
Norbertas Kairys ◽  
Lu Yang ◽  
Ru-Jin Huang ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Source Apportionment ◽  
Elemental Carbon ◽  
Raw Materials ◽  
Total Carbon ◽  
Carbonaceous Aerosols ◽  
Thermal Methods ◽  
Dual Isotope ◽  
Atmospheric Processing ◽  
Split Point

&lt;p&gt;Isotopic source apportionment is commonly used to gain insight into sources and atmospheric processing of carbonaceous aerosols. Since elemental carbon (EC) is chemically stable, it is possible to apportion the main sources of EC (coal/biomass burning and traffic emissions) using a dual &lt;sup&gt;14&lt;/sup&gt;C-&lt;sup&gt;13&lt;/sup&gt;C isotope approach. However, dual-isotope source apportionment crucially relies on accurate knowledge of the &lt;sup&gt;13&lt;/sup&gt;C source signatures, which are seldom measured directly for EC. In this work, we present extensive measurements of organic carbon (OC) and EC &lt;sup&gt;13&lt;/sup&gt;C signatures for relevant sources in China. The EC &lt;sup&gt;13&lt;/sup&gt;C source signatures are provided first time using the optical split point in a thermal-optical analyzer to isolate EC, which can greatly reduce the influence of pyrolyzed organic carbon (pOC). A series of sensitivity studies (pOC/EC separation) were conducted to investigate the reliability of our method and its relation to other EC isolation methods. Meanwhile, we summarized and compared the literature &lt;sup&gt;13&lt;/sup&gt;C signatures in detail of raw source materials, total carbon (TC) and EC using a variety of thermal methods. Finally, we recommend composite EC &lt;sup&gt;13&lt;/sup&gt;C source signatures with uncertainties and detailed application conditions. There are two points worth noting. First, the traffic &lt;sup&gt;13&lt;/sup&gt;C signatures of raw materials and EC are separated into three groups according to geographical distribution. Second, the EC &lt;sup&gt;13&lt;/sup&gt;C signature of C4 plant combustion can be influenced greatly if pOC and EC are not well separated, so the thermal-optical method is necessary. Using these EC &lt;sup&gt;13&lt;/sup&gt;C source signatures in an exemplary dual-isotope source apportionment study shows improvement in precision. In addition, some interesting distinct and repeatable patterns were discovered in &lt;sup&gt;13&lt;/sup&gt;C source signatures of semi-volatile, low-volatile, and non-volatile primary OC fractions.&lt;/p&gt;

scholarly journals Ionic and carbonaceous compositions of PM<sub>10</sub>, PM<sub>2.5</sub> and PM<sub>1.0</sub> at Gosan ABC Superstation and their ratios as source signature

2012 ◽  
Vol 12 (4) ◽  
pp. 2007-2024 ◽  
Author(s):  
S. Lim ◽  
M. Lee ◽  
G. Lee ◽  
S. Kim ◽  
S. Yoon ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Motor Vehicle ◽  
Southern China ◽  
Regional Scale ◽  
East Sea ◽  
Carbonaceous Aerosols ◽  
Vehicle Exhaust ◽  
Study Region ◽  
Air Masses ◽  
Pm2.5 And Pm10

Abstract. PM1.0, PM2.5, and PM10 were sampled at Gosan ABC Superstation on Jeju Island from August 2007 to September 2008. The carbonaceous aerosols were quantified with the thermal/optical reflectance (TOR) method, which produced five organic carbon (OC) fractions, OC1, OC2, OC3, OC4, and pyrolyzed organic carbon (OP), and three elemental carbon (EC) fractions, EC1, EC2, and EC3. The mean mass concentrations of PM1.0, PM2.5, and PM10 were 13.7 μg m−3, 17.2 μg m−3, and 28.4 μg m−3, respectively. The averaged mass fractions of OC and EC were 23.0% and 10.4% for PM1.0, 22.9% and 9.8% for PM2.5, and 16.4% and 6.0% for PM10. Among the OC and EC sub-components, OC2 and EC2+3 were enriched in the fine mode, but OC3 and OC4 in the coarse mode. The filter-based PM1.0 EC agreed well with black carbon (BC) measured by an Aethalometer, and PM10 EC was higher than BC, implying less light absorption by larger particles. EC was well correlated with sulfate, resulting in good relationships of sulfate with both aerosol scattering coefficient measured by Nephelometer and BC concentration. Our measurements of EC confirmed the definition of EC1 as char-EC emitted from smoldering combustion and EC2+3 as soot-EC generated from higher-temperature combustion such as motor vehicle exhaust and coal combustion (Han et al., 2010). In particular, EC1 was strongly correlated with potassium, a traditional biomass burning indicator, except during the summer, when the ratio of EC1 to EC2+3 was the lowest. We also found the ratios of major chemical species to be a useful tool to constrain the main sources of aerosols, by which the five air masses were well distinguished: Siberia, Beijing, Shanghai, Yellow Sea, and East Sea types. Except Siberian air, the continental background of the study region, Beijing plumes showed the highest EC1 (and OP) to sulfate ratio, which implies that this air mass had the highest net warming by aerosols of the four air masses. Shanghai-type air, which was heavily influenced by southern China, showed the highest sulfate enhancement. The highest EC2+3/EC1 ratio was found in aged East Sea air, demonstrating a significant influence of motor vehicle emissions from South Korea and Japan and less influence from industrial regions of China. The high ratio results from the longer residence time and less sensitivity to wet scavenging of EC2+3 compared to EC1, indicating that soot-EC could have greater consequence in regional-scale warming.

scholarly journals Decreasing concentrations of carbonaceous aerosols in China from 2003 to 2013

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yan Cheng ◽  
Judith C. Chow ◽  
John G. Watson ◽  
Jiamao Zhou ◽  
Suixin Liu ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Coal Combustion ◽  
Elemental Carbon ◽  
Total Carbon ◽  
Carbonaceous Aerosols ◽  
Carbon Reduction ◽  
Northern Cities ◽  
Secondary Organic Carbon ◽  
Emission Changes ◽  
Carbon Concentrations

AbstractCarbonaceous aerosols were characterized in 19 Chinese cities during winter and summer of 2013. Measurements of organic carbon (OC) and elemental carbon (EC) levels were compared with those from 14 corresponding cities sampled in 2003 to evaluate effects of emission changes over a decade. Average winter and summer OC and EC decreased by 32% and 17%, respectively, from 2003 to 2013, corresponding to nationwide emission control policies implemented since 2006. The extent of carbon reduction varied by season and by location. Larger reductions were found for secondary organic carbon (SOC, 49%) than primary organic carbon (POC, 25%). PM2.5 mass and total carbon concentrations were three to four times higher during winter than summer especially in the northern cities that use coal combustion for heating.

scholarly journals Measurement report: Characterization of severe spring haze episodes and influences of long-range transport in the Seoul metropolitan area in March 2019

2020 ◽  
Author(s):  
Hwajin Kim ◽  
Qi Zhang ◽  
Yele Sun
Keyword(s):  
Metropolitan Area ◽  
Temporal Trends ◽  
Multiple Linear Regression Model ◽  
Early Spring ◽  
First Episode ◽  
Regional Transport ◽  
Air Masses ◽  
Seoul Metropolitan Area ◽  
Local Emissions ◽  
Haze Days

Abstract. Severe haze episodes have occurred frequently in the Seoul metropolitan area (SMA) and throughout East Asian countries, especially during winter and early spring. Although notable progress has been attained in understanding these issues, the causes of severe haze formation have not yet been fully investigated. SMA haze is especially difficult to understand because the area is impacted by both local emissions from anthropogenic and biogenic activities and emissions transported from upwind sources. Here, we investigated the emission sources and formation processes of particulate matter (PM) during three haze episodes measured in early spring of 2019, from February 22 to April 2, using a high-resolution aerosol mass spectrometer (HR-AMS). Overall, the average concentration of nonrefractory submicron aerosol (NR-PM1) + BC was 35.1 μg m−3, which was composed of 38 % organics, 12 % SO4, 30 % NO3, 13 % NH4 and 5 % BC. The organics had an average oxygen-to-carbon (O / C) ratio of 0.52 and an average organic mass-to-carbon (OM / OC) ratio of 1.86. Seven distinct sources of organic aerosols (OA) were identified via positive matrix factorization (PMF) analysis of the HR-AMS data: vehicle-emitted hydrocarbon-like OA (HOA), cooking OA (COA), solid fuel burning-emitted OA (SFOA) and 4 different types of oxidized secondary OA with varying oxidation degrees and temporal trends. Of the 40 days of the measurement period, 23 were identified as haze days (daily average: > 35 μg m−3), during which three severe haze episodes were recorded. In particular, PM1 concentration exceeded 100 μg m3 during the first episode when an alert was issued and strict emission controls were implemented in the SMA. Our results showed that nitrate dominated during the three haze episodes and accounted for 39–43 % of the PM1 concentration on average (vs. 21–24 % during the low-loading period), for which there were indications of regional transport influences. Two regional transport-influenced OOA, i.e., less oxidized OOA2 (LO-OOA2) and more oxidized OOA2 (MO-OOA2), contributed substantially to the total PM1 during the haze period (12–14 % vs. 7 % during the low-loading period), as well. In contrast, HOA and COA only contributed little (4–8 % vs. 4–6 % during the low-loading period) to the PM1 concentration during the haze days, indicating that local emissions were likely not the main reason for the severe haze issues. Hence, from simultaneous downwind (SMA) and upwind (Beijing) measurements using AMS and ACSM (aerosol chemical speciation monitor) over the same period, the temporal variations in PM1 and each chemical species showed peak values on the order of Beijing (upwind)) to the SMA for approximately two days. Furthermore, lead (Pb) derived from HR-AMS measurements was observed to increase significantly during the haze period and showed good correlations with MO-OOA2 and LO-OOA2, consistent with regional sources. Multiple linear regression model indicated that the transported regionally processed air masses contributed significantly to Pb in the SMA (31 %), especially during the haze period although the local burning also important by contributing 38 %. The above results suggest that regional transport of polluted air masses might have played an important role in the formation of the haze episodes in the SMA during early spring.

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