Urban Site Of Gwangju Research Articles

늦가을에 도시와 부두 지점에서 측정한 초미세먼지의 화학적 성상과 선박 운항이 에어로졸 입자의 광 흡수에 미치는 영향

늦가을에 도시와 부두 지점에서 측정한 초미세먼지의 화학적 성상과 선박 운항이 에어로졸 입자의 광 흡수에 미치는 영향

Comprehensive characterization of PM2.5 using chemical, optical, and spectroscopic methods during pollution episodes at an urban site in Gwangju, Korea

In this study, PM2.5 samples collected between October 29 and December 23, 2018 at a roadway site in Gwangju, Korea, were comprehensively characterized by chemical, optical, and spectroscopic methods. Aerosol light absorption was observed with a time resolution of 1 min using a dual-spot aethalometer. An Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy analysis was also applied to characterize organic and inorganic components in the PM2.5 samples. Three PM2.5 pollution episodes which exceeded the 24-hr Korean PM2.5 standard (35 μg/m3) were classified; Episode I was associated with local air stagnation and long-range transportation of aerosol particles from northeast China and upwind regions; Episode II was affected by Asian dust (AD) particles and local pollution under low relative humidity (RH) conditions; and Episode III was strongly associated with accumulation of local pollution due to very high RH and low wind speed, along with regional transport of aerosol particles from eastern China.The contribution of organic aerosols to PM2.5 was higher during episodes I and II than during episode III, while the contribution of NO3− particles was greater during episode III, possibly due to very high RH and low wind speed conditions. Unexpectedly, SO42− was not an important component of PM2.5 during the three episodes. The light absorption coefficient (bBrC,370) of brown carbon (BrC) at 370 nm was estimated to range from 9 Mm−1 during episode II to 14 Mm−1 during episode III, but the contribution of bBrC,370 to total aerosol absorption was the lowest during episode III. Multiple linear regression analysis indicated that the contributions of the traffic emissions, biomass burning (BB) emissions, and secondary formation processes to bBrC,370 absorption were, on average, 37, 39, and 14% of the total estimated bBrC,370, respectively, suggesting that primary traffic emissions are an important contributor to BrC absorption at the roadway site. ATR-FTIR analysis showed that aliphatic carbon group (C–H), carbonyl group (CO), ammonium, sulfate, and nitrate were identified in all filter samples collected during the three pollution episodes; the corresponding bands had the highest intensities in the filter sample from episode III. However, the presence of mineral dusts related to hydroxyl group (-OH), gypsum, Al–Al–OH group, CO32−, and SO32− were clearly detected at the absorbance bands at 3400–3700 and 650–900 cm−1 in the AD sample only (episode II). Furthermore, the absorbance bands observed at 2910 and 2850 cm−1 during the pollution episodes were assigned to methylene groups (–CH2–), which are associated with BB emissions, and the intensities of those bands during pollution episodes were consistent with the concentrations of BB indicators (e.g., levoglucosan and K+). These FTIR method can provide valuable chemical insights into the nature of the organic and inorganic components present in ambient aerosol particles during different pollution episodes.

Chemical characterization and source apportionment of PM2.5 at an urban site in Gwangju, Korea

It is crucial to investigate the chemical species that cause increases in PM2.5 concentration and to quantitatively estimate source contributions to PM2.5 in urban environments in order to establish strategies to control anthropogenic air pollution. In this study, measurements of 24-hr integrated PM2.5 were performed for 1 year at an urban site in Gwangju, Korea. The collected samples were analyzed for organic and elemental carbon (OC and EC), water-soluble OC (WSOC), eight ionic species, and elemental species, which were used to estimate source contribution of PM2.5 using a positive matrix factorization (PMF) model.The dominant species that contributed to PM2.5 during the study period was organic matter (OM), which accounted for 24% of PM2.5. The major chemical species resulting in PM2.5 pollution episodes (>24-hr Korean PM2.5 standard of 35 μg/m3) depended on the season. For example, PM2.5 increases in winter were strongly associated with increases in secondary nitrate and OM concentrations, while rapid increases in secondary sulfate concentration brought on summertime PM2.5 increases.A total of eight sources of PM2.5 were identified using PMF analysis: secondary nitrate (26%), secondary sulfate (23%), traffic emissions (14%), metallurgical and smelting processes (11%), brake and tire wearing processes (9%), biomass burning emission (8%), crustal source (7%), and industrial sources (1%). The brake and tire wearing processes were a non-negligible contributor to total PM2.5 at the study site, accounting for 7% of PM2.5 in summer and 18% in fall. Metallurgical and smelting processes, which are highly enriched in elements such as Pb, Cu, As, Se, and Zn, were also found to be an important source of PM2.5 at the study site, contributing 7% of PM2.5 in summer and 14% in fall. Moreover, the total contribution of mobile-related emissions, such as vehicles and brake and tire wearing processes, to PM2.5 ranged from 15.2% in summer to 40.0% in winter with an average of 23%. Overall, the results of this study suggest that control of mobile-related sources is crucial to reducing the high PM2.5 levels in the Gwangju metropolitan area.

2019년 11월 측정 광주광역시 대기 중 수용성 유·무기 입자의 크기분포 특성

2019년 11월 측정 광주광역시 대기 중 수용성 유·무기 입자의 크기분포 특성

광주 지역에서 늦가을 황사 발생 시 대기 에어로졸 입자의 크기 분포 변화

광주 지역에서 늦가을 황사 발생 시 대기 에어로졸 입자의 크기 분포 변화

광주 지역에서 aethalometer 측정 블랙 카본 입자의 질량흡수단면 평가

광주 지역에서 aethalometer 측정 블랙 카본 입자의 질량흡수단면 평가

Absorption properties and size distribution of aerosol particles during the fall season at an urban site of Gwangju, Korea

Absorption properties and size distribution of aerosol particles during the fall season at an urban site of Gwangju, Korea

Optical absorption characteristics of brown carbon aerosols during the KORUS-AQ campaign at an urban site

This study investigates the absorption characteristics of brown carbon (BrC) obtained from water and methanol extracts of fine particulate matter measured at an urban site in Gwangju, Korea during the KOREA U.S. – Air Quality campaign (May 2–June 11, 2016). The measurement period was classified into two intervals: biomass burning (BB) and non-BB periods. During the non-BB period, water-soluble organic carbon (WSOC) and humic-like substances (HULIS) primarily resulted from secondary organic aerosol (SOA) formation and primary vehicle emissions. Water-soluble organic aerosols during the BB period, meanwhile, were closely related to SOA formation and regionally transported BB emissions.The light absorption coefficient measured at 365nm (babs,365) by methanol extracts was 2.6 and 6.1 times higher than the coefficients from the water and HULIS extracts, respectively, indicating the importance of BrC absorption by water-insoluble organic carbon. This was demonstrated by a good correlation between the water-insoluble BrC absorption and the elemental carbon concentration. A comparison of babs,365 between the methanol- and water-extracted BrC indicated that water-insoluble BrC accounted for approximately 61% (33–86%) of the total BrC absorption. The contributions of SOA, primary BB emissions, and traffic emissions to the water extract babs,365 were estimated using a stepwise multiple linear regression (MLR) analysis and found to be 1.17±0.55, 0.65±0.62, and 0.25±0.09Mm−1, respectively, accounting for 59.6, 26.1, and 14.3% of the absorption coefficient by the water-soluble BrC. Further, it was determined that the contribution of the BB emissions to the water-soluble BrC absorption was approximately two times higher in the BB period than in the non-BB period.The average absorption Ångstrӧm exponent was 4.8±0.3, 5.3±0.7, and 6.8±0.8 for the methanol, water, and HULIS extracts, respectively. The average mass absorption efficiency (MAE365) of methanol extracted BrC was 1.3±0.4m2/g·C. Water- and HULIS-extracted BrC had a MAE365 of 1.0±0.3 and 0.8±0.3m2/g·C, respectively. These results suggest that methanol-extracted BrC could provide a better estimation of BrC absorption compared to WSOC and HULIS.

Influence of haze pollution on water-soluble chemical species in PM2.5 and size-resolved particles at an urban site during fall

To investigate the influence of haze on the chemical composition and formation processes of ambient aerosol particles, PM2.5 and size-segregated aerosol particles were collected daily during fall at an urban site of Gwangju, Korea. During the study period, the total concentration of secondary ionic species (SIS) contributed an average of 43.9% to the PM2.5, whereas the contribution of SIS to the PM2.5 during the haze period was 62.3%. The NO3− and SO42− concentrations in PM2.5 during the haze period were highly elevated, being 13.4 and 5.0 times higher than those during non-haze period, respectively. The PM, NO3−, SO42−, oxalate, water-soluble organic carbon (WSOC), and humic-like substances (HULIS) had tri-modal size distributions peaks at 0.32, 1.0, and 5.2μm during the non-haze and haze periods. However, during the non-haze period they exhibited dominant size distributions at the condensation mode peaking at 0.32μm, while on October 21 when the heaviest haze event occurred, they had predominant droplet mode size distributions peaking at 1.00μm. Moreover, strong correlations of WSOC and HULIS with SO42−, oxalate, and K+ at particle sizes of <1.8μm indicate that secondary processes and emissions from biomass burning could be responsible for WSOC and HULIS formations. It was found that the factors affecting haze formation could be the local stable synoptic conditions, including the weak surface winds and high surface pressures, the long-range transportation of haze from eastern China and upwind regions of the Korean peninsula, as well as the locally emitted and produced aerosol particles.

Relationship between carbonaceous components and aerosol light absorption during winter at an urban site of Gwangju, Korea

To examine the relationship between the chemical composition of light-absorbing organic aerosols and the absorption properties of the aerosols, daily PM2.5 samples were collected during winter at an urban site of Gwangju, Korea, and analyzed for organic carbon and elemental carbon (OC and EC), water-soluble organic carbon (WSOC), humic-like substances (HULIS), and water-soluble inorganic substances. The real-time black carbon (BC) concentration in PM2.5 was also measured using a dual-spot aethalometer. During the study period, average WSOC/OC and HULIS-C/WSOC ratios were 0.53 and 0.52, respectively. K+/EC and K+/OC ratios indicate that biomass burning (BB) emissions are a possible source of the observed carbonaceous aerosols and K+. Moderate-to-strong correlations of HULIS with NO3−, oxalate, SO42−, K+, CO, and ΔBC (=BC@370nm−BC@880nm) suggest that in addition to the primary BB emissions, secondary processing is another important contributor to the formation of HULIS in winter at the site.The average absorption Ångstrӧm exponent (α) of fine aerosols for the wavelengths of 370–950nm and 590–950nm was 1.29 and 1.18, respectively, but the aerosol α value was higher in the near UV wavelength range (370–520nm), with an average of 1.51 (0.76–2.36), indicating that aerosol absorption characteristics during winter were influenced by BB aerosol sources, as well as by traffic emissions. Over the study period, the α370–520nm value during the highest EC, highest OC, and Asian dust events was 1.42±0.10 (1.26–1.59), 1.44±0.15 (1.16–1.68), and 1.90±0.28 (1.54–2.36), respectively. Higher α370–520nm values during the Asian dust event were attributed to the influence of dust particles. In addition, the light absorption coefficients of aerosols at 370nm were strongly correlated with OC (R2=0.76), water-insoluble OC (R2=0.70), and water-soluble HULIS (R2=0.64). These tight correlations suggest that water-insoluble fractions of OC, as well as the water-soluble brown carbon, could be important contributors to aerosol light absorption. This study demonstrates that a newly-developed dual-spot aethalometer could be utilized to characterize light absorption properties of organic aerosols and dust particles.

Optical and thermal characteristics of carbonaceous aerosols measured at an urban site in Gwangju, Korea, in the winter of 2011

ABSTRACTCarbonaceous components (organic carbon [OC] and elemental carbon [EC]) and optical properties (light absorption and scattering) of fine particulate matter (aerodynamic diameter <2.5 μm; PM2.5) were simultaneously measured at an urban site in Gwangju, Korea, during the winter of 2011. OC was further classified into OC1, OC2, OC3, and OC4, based on a temperature protocol using a Sunset OC/EC analyzer. The average OC and EC concentrations were 5.0 ± 2.5 and 1.7 ± 0.9 μg C m−3, respectively. The average single-scattering albedo (SSA) at a wavelength of 550 nm was 0.58 ± 0.11, suggesting that the aerosols observed in the winter of 2011 had a local warming effect in this area. During the whole sampling period, “stagnant PM” and “long-range transport PM” events were identified. The light absorption coefficient (babs) was higher during the stagnant PM event than during the long-range transport PM event due to the existence of abundant light-absorbing OC during the stagnant PM event. In particular, the OC2 and OC3 concentrations were higher during the stagnant PM event than those during the long-range transport event, suggesting that OC2 and OC3 might be more related to the light-absorbing OC. The light scattering coefficient (bscat) was similar between the events. On average, the mass absorption efficiency attributed to EC (σEC) was 9.6 m2 g−1, whereas the efficiency attributed to OC (σOC) was 1.8 m2 g−1 at λ = 550 nm. Furthermore, the σEC is comparable among the PM event days, but the σOC for the stagnant PM event was significantly higher than that for the long-range transport PM event (1.7 vs. 0.5).Implications: Optical and thermal properties of carbonaceous aerosol were measured at Gwangju, and carbonaceous aerosol concentration and optical property varied between “stagnant PM” and “long-range transport PM” events. More abundant light absorbing OC was observed during the stagnant PM event.

도시지역 PM&lt;sub&gt;2.5&lt;/sub&gt;의 HULIS 화학 특성 및 발생 과정 조사

Little information on HUmic-Like Substances (HULIS) in ambient particulate matter has been reported yet in Korea. HULIS makes up a significant fraction of the water-soluble organic mass in the atmospheric aerosols and influence their water uptake properties. In this study 24-hr PM2.5 samples were collected between December 2013 and October 2014 at an urban site in Gwangju and analyzed for organic carbon (OC), elemental carbon (EC), watersoluble OC (WSOC), HULIS, and ionic species, to investigate possible sources and formation processes of HULIS. HULIS was separated using solid phase extraction method and quantified by total organic carbon analyzer. During the study period, HULIS concentration ranged from 0.19 to 5.65 μgC/m with an average of 1.83±1.22 μgC/m, accounting for on average 45% of the WSOC (12~73%), with higher in cold season than in warm season. Strong correlation of WSOC with HULIS (R = 0.91) indicates their similar chemical characteristics. On the basis of the relationships between HULIS and a variety of chemical species (EC, K, NO3-, SO4, and oxalate), it was postulated that HULIS observed during summer and winter were likely attributed to secondary formation and primary emissions from biomass burning (BB) and traffics. Stronger correlation of HULIS with K, which is a BB tracer, in winter (R = 0.81) than in summer (R = 0.66), suggests more significant contribution of BB emissions in winter to the observed HULIS. It is interesting to note that BB emissions may also have an influence on the HULIS in summer, but further study using levoglucosan that is a unique organic marker of BB emissions is required during summer. Higher correlation between HULIS and oxalate, which is mainly formed through cloud processing and/or photochemical oxidation processes, was found in the summer (R = 0.76) than in the winter (R = 0.63), reflecting a high fraction of secondary organic aerosol in the summer.

Characterization of Organic Aerosol Particles Observed during Asian Dust Events in Spring 2010

Between 20 March and 4 April, 2010, 24-hr PM2.5 measurements were carried out at an urban site in Gwangju, Korea, to examine the variations in the composition of its chemical constituents among dust storm (DS) events, haze pollution, and typical sampling (TS) conditions. A very heavy Asian DS (DS1) and a minor DS (DS2) occurred at the site on 20 and 23 March, 2010, respectively. The concentrations of organic matter, NO3–, SO42–, and the predicted crustal material made a contribution to the observed PM2.5 of 12.9, 9.7, 12.9, and 36.9% for DS1, 23.8, 17.1, 9.9, and 29.7% for DS2, and 24.9, 20.2, 10.3, and 17.6% for the haze event, respectively. Over the study period, the water-soluble organic carbon (WSOC)/OC and hydrophilic WSOC (WSOCHPI)/WSOC ratios ranged from 0.35 to 0.54 and from 0.15 to 0.61, respectively, with the highest ratios occurring during DS1. The concentration of WSOCHPI during DS1 was about 2–3 times higher than that during the TS period. The strong correlation between WSOC/OC and WSOCHPI/WSOC (R2 = 0.84) clearly indicates that the increase in the WSOC/OC ratio can be attributed to the increased concentration of WSOCHPI, suggesting that the aerosol sample collected during DS1 was more aged or atmospherically processed than the samples collected during the TS. In addition to the association between the WSOC/OC and WSOCHPI/WSOC ratios, strong correlations between the oxalate and SO42– concentrations (R2 = 0.74), and between the WSOCHPI and SO42– concentrations (R2 = 0.69), suggest that the WSOCHPI observed at the site was produced by atmospheric transformation processes similar to those seen with SO42– and oxalate. In contrast, the hydrophobic WSOC (WSOCHPO) concentration dominated in the other sampling periods, except for DS1, and accounted for 71.1–84.7% of WSOC. Based on the results of previous studies, the higher WSOCHPO/WSOC ratio during the TS indicates that the primary combustion emissions were important sources of the WSOCHPO fraction at this site.

대기입자의 원소성분 배출특성연구를 위한 반-연속식 입자채취시스템 적용

Aerosol slurry samples were collected in 60-min interval using Korean Semi-continuous Elements in Aerosol Sampler (KSEAS) between May 19 and June 6, 2010 at an urban site of Gwangju. The <TEX>$PM_{2.5}$</TEX> samples were collected with a flow rate of 16.7 L/min and particles are grown by condensation of water vapor in a condenser maintained at <TEX>${\sim}5^{\circ}C$</TEX> after saturation by direct injection of steam. The resulting droplets are collected in a liquid slurry with a airdroplet separator. Concentrations of 16 elements (Al, Fe, Mn, Ca, K, Cu, Zn, Pb, Cd, Cr, Ti, V, Ni, Co, As, Se) in the collected slurry samples were determined off-line by ICP-MS. KSEAS sample analysis encompassed the sampling periods for which 24-hr average elemental species concentrations were calculated for comparison with those derived from 24-hr integrated filter samples. Relationship between elemental species measured by two methods indicated high correlation coefficients (r), mostly greater than r of 0.80. However, we note that concentrations of Al, K, Ca, Mn, and Fe, which are often associated with crustal elemental particles, in the KSEAS samples, were substantially lower (1.4~11 times) than those found in the typical filter-based samples. This discrepancy is probably due to difficulties in transferring insoluble dust particles to the collection vials in the KSEAS. Temporal profiles of elemental concentrations indicate that some transient events in their concentrations are observed over the sampling periods. For the elemental species studied, atmospheric concentrations during the transient events increased by factors of 4 in Mn~80 in Zn, compared to their background levels. Principle component analyses were applied to the hourly KSEAS data sets to identify sources affecting the concentrations of the metal constituents observed. In this study, we conclude that hourly measurements for particle-bound elemental constituents were extremely useful for revealing the short-term variability in their concentrations and developing insights into their sources.

대기 에어로졸 검댕입자 측정을 위한 두 aethalometer의 상호비교

Recently, a real-time, pocket-sized aethalometer (microAeth model AE51) has been developed by Magee Scientific Inc. for measuring the concentration of black carbon in the atmosphere. In this study, two aethalometers, models AE-16 and AE-51, which measure the optical absorption of carbon particles at infrared 880 nm, were operated at time interval of 5-min between January 9 and February 10, 2010 at an urban site of Gwangju, to compare the accuracy of black carbon (BC) concentrations reported from the AE-51 model and to investigate reasonable sampling time of filter media in the AE-51. The air samples in the AE-51 and AE-16 models are collected on T60 (Teflon coated glass fiber) filter media (filter spot area: 0.07 ) and quartz fiber roll-tape filter (filter spot area: 1.67 ), respectively. Real-time measurement results indicate that when the filters were clean, the AE-51 BC was greater than or similar to the AE-16 BC data. However as the filter spots become darker, the AE-16 BC concentrations were higher than the AE-51 BC data and the difference in the BC concentrations from two AE models becomes gradually increased. Relative error in the AE-51 and AE-16 BC concentrations showed significance difference depending on used time of the filter in the AE-51 model, weather pattern, levels of air pollution, etc, ranging from 11.5% (used time of the filter in AE-51: 1,595 min) to 52.5% (used time of the filter in AE-51: 2,085 min). When considering the used time of one filter ticket in the AE-51 model and difference (or relative error %) between AE-16 and AE-51 BC concentrations, it is recommended that the standard sampling time per one filter ticket within the AE-51 model be less than approximately 24 hr (1,440 min) under the normal weather conditions except for severe haze and mist events.

Derivation of the Ambient Nitrogen Dioxide Mixing Ratio over a Traffic Road Site Based on Simultaneous Measurements Using a Ground-based UV Scanning Spectrograph

Simultaneous measurements using a scanning spectrograph system and transmissometer were performed for the first time over an urban site in Gwangju, Korea, to derive the ambient NO2 volume mixing ratio. The differential slant column densities retrieved from the scanning spectrograph system were converted to volume mixing ratios using the light traveling distance along the scanning line of sight derived from the transmissometer light extinction coefficients. To assess the performance of this system, we compared the derived NO2 volume mixing ratios with those measured by an in situ chemiluminescence monitor under various atmospheric conditions. For a cloudless atmosphere, the linear correlation coefficient (R) between the two data sets (i.e., data derived from the scanning spectrograph and from the in situ monitor) was 0.81; the value for a cloudy atmosphere was 0.69. The two sets of NO2 volume mixing ratios were also compared for various wind speeds. We also consider the measurement errors, as estimated from an error propagation analysis.

Tracking sources and behaviors of water-soluble organic carbon in fine particulate matter measured at an urban site in Korea

PM 2.5 water-soluble organic carbon (WSOC) was measured over 24-h periods with organic carbon and elemental carbon (OC and EC) at an urban site in Gwangju, Korea, during summer (1 June–22 August 2008) and winter (26 November 2008–27 February 2009). The average mass concentrations of OC and WSOC were 5.0 ± 2.9 μg C m −3 and 2.8 ± 1.6 μg C m −3 during summer, respectively, and 8.4 ± 4.6 μg C m −3 and 3.7 ± 2.5 μg C m −3 during winter, respectively. The WSOC/EC and WSOC/OC ratios were 1.74 ± 0.60 and 0.55 ± 0.10 in summer, and 1.30 ± 0.70 and 0.43 ± 0.11 in winter, respectively. According to the results of air mass backward trajectory analysis, high fractions of WSOC to OC in the study region, compared to those reported in many other urban sites, could be explained by the atmospheric transport of water-soluble organic species from upwind regions, i.e., large-scale Steel Works and national industrial complexes located in the southeastern and eastern directions of the sampling site and northeastern regions (Beijing, Shenyang, and Shanghai) of China in the summer, and the northeastern regions of China in the winter. The secondary OC concentrations, estimated using the EC-tracer method, accounted for 26.9 ± 19.1% (0.0–65.0%) and 24.3 ± 19.5% (0.0–73.5%) of the measured OC in summer and winter, respectively. Higher correlation between secondary OC and WSOC was found in the summer ( R 2 = 0.78) than in the winter ( R 2 = 0.34), reflecting a high fraction of secondary WSOC in the summer. The entire winter sampling period was separated into two periods, i.e., winter periods “A” (Nov 26 2008–Jan 8 2009) and “B” (Jan 19–Feb 27 2009), due to the existence of open burning activities around the sampling site. Highly enriched behaviors of potassium ion (K + ) and WSOC concentrations during the winter “A” period are in accordance with the fact that open burning of wood and vegetation debris at a construction working place near the sampling site was occasionally observed. The moderate correlations between water- soluble K + and WSOC concentrations suggest that some of the WSOC observed during summer and winter could be attributed to the impact of biomass burning.

지표면 대기중 가스상오염물질 다경로 동시 원격 모니터링을 위한 CMP-DOAS 개발: 첫 개발 사례 및 이산화질소 측정 연구

Concurrent Multi Path-Differential Optical Absorption Spectroscopy (CMP-DOAS) is a novel active optical system to measure simultaneously ambient trace gases (such as , , , and HCHO) present on several light paths. The CMP-DOAS system consists of a 2D CCD camera, spectrometer, receiving telescopes, and artificial light sources. The system receives spectra, which have been transported through several paths. It also covers wavelength ranges of which trace gases of interest share at the same time. This study presents the instrumental setup of a CMP-DOAS in detail. A field campaign for a comparative measurement was carried out at an urban site in Gwangju for a month on January 2009. mixing ratios measured by the CMP-DOAS system and in-situ analyzers were in good agreement by 83%. It demonstrates the high capacities of the CMP-DOAS technique to cover atmospheric trace gases dispersed across wide light paths.

2008년 광주지역 검댕입자 특성 및 광학적 산란효과 보상

Black carbon (BC) concentrations were measured with an aethalometer (AE-16, 880 nm) at time interval of 5-min at an urban site of Gwangju over a year 2008. 24-hr filter-based integrated measurements of particles were also made at the same site during the winter and summer intensive periods to test any optical loading bias in the raw BC data measured by aethalometer. BC concentration was higher in winter than in summer, possibly due to increase in emissions from energy consumption and poor dispersion with reduction of boundary layer in winter. Also temporal cycles of BC indicate that short-term transient spikes were common, occurring primarily during the rush-hour periods. A similar feature was also observed in diurnal concentration cycle of CO, mainly emitted from motor vehicles. When both low wind speed and weather patterns such as mist, haze and etc were combined, high BC concentrations frequently occurred. The amount of optical loading effect described by the k factor showed the seasonal variation, ranging from 0.0003 to 0.0036. This implies that optical loading effect is not seen at all times. From the comparison between the filter-based elemental carbon (EC) and aethalometer BC data, it was found that the loading compensated BC values were more reasonable than the raw BC ones reported from the aethalometer.

여름 및 겨울철 광주지역 대기 에어로졸 입자의 유기탄소 특성

To characterize organic and elemental carbon (OC and EC), and water-soluble organic carbon (WSOC) contents, daily measurements were performed in August 2006 (summer) and Jan 12 2007 (winter) at an urban site of Gwangju. Daily size-segregated aerosol samples were also collected for WSOC analysis. No clear seasonal variations in EC and WSOC concentrations were observed, while seasonal differences in OC concentration, and OC/EC and WSOC/EC ratios were shown. The WSOC/OC ratio showed higher value in summer (0.56) than in winter (0.40), reflecting the greater enhancement of secondary WSOC formation at the site in summer. Secondary WSOC concentrations estimated using EC tracer method were in the range (average ) and , respectively, accounting for (average 16.8%) and (average 13.1 %) of the measured WSOC concentrations in summer and winter. Sometimes higher WSOC/OC ratio in winter than that in summer could be attributed to two reasons. One is that the stable atmospheric condition often appears in winter, and the prolonged residence time would strengthen atmospheric oxidation of volatile organic compounds. The other is that decrease of ambient temperature in winter would enhance the condensation of volatile secondary WSOC on pre-existing aerosols. In summertime, atmospheric aerosols and WSOC concentrations showed bimodal size distributions, peaking at the size ranges (condensation mode) and (coarse mode), respectively. During the wintertime, atmospheric aerosols showed a bimodal character, while WSOC concentrations showed a unimodal pattern. Size distributions of atmospheric aerosols and WSOC with a peak in the size range were observed for most of the measurement periods. On January 17, however, atmospheric aerosols and WOSC exhibited size distributions with modal peaks in the size range , suggesting that the aerosol particles collected on that day could be expected to be more aged, i.e, longer residence time, than the aerosols at other sampling periods.