Number size distribution of atmospheric aerosols during ACE-Asia dust and precipitation events

Kim, J.,Jung, C.H.,Choi, B.-C.,Oh, S.-N.,Brechtel, F.J.,Yoon, S.-C.,Kim, S.-W. Pergamon Press ; Elsevier [distribution] 2007 Atmospheric environment Vol.41 No.23

Measurements of size-resolved particle number concentrations during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) field campaign were made at the Gosan super-site, South Korea. In East Asia, dust and precipitation phenomena play a crucial role in atmospheric environment and climate studies because they are major sources and sinks of atmospheric aerosols, especially in the springtime. Total Ozone Mapping Spectrometer (TOMS) Aerosol Index and backward trajectories are analyzed to investigate the spatial and temporal evolution of dust storms. The size distributions between dust and non-dust periods and times with and without precipitation are compared. In order to understand the temporal evolution of the aerosol size distribution during dust and precipitation events, a simple aerosol dynamics model is employed. The model predicted and observed size distributions are compared with the measured data. The results show that the coarse mode particle number concentrations increase by a factor of 10-16 during dust events. During precipitation, however, particles in the coarse mode are scavenged by impaction mechanism. It is found that the larger particles are more efficiently scavenged. The degree of scavenged particle varies depending on the rainfall rate, raindrop size distribution and aerosol size distribution.

Aerosol size distributions observed at Naiman in the Asian dust source region of Inner Mongolia

Park, S.U.,Park, M.S. Pergamon Press ; Elsevier [distribution] 2014 Atmospheric environment Vol.82 No.-

Aerosol size distributions of observed mass concentrations at the Naiman site in Inner Mongolia that is one of the major Asian dust source regions have been examined for the period from April 2010 to July 2012. The total number of 262 sampled data using the 10-stage quartz crystal microbalance (QCM) cascade impactor is obtained by presetting the frequency changes of 40 Hz during April 2010, 60 Hz for the period of 28 April-16 September 2010 and 70 Hz from 1 November 2010-29 July 2012. The total mass concentrations (PM<SUB>10</SUB>) measured by the QCM cascade impactor are modified to have the same sampling time of 60 min with the help of the 1-h averaged PM<SUB>10</SUB> concentration measured by the beta gauge at the same site. These modified QCM data are classified into the local dust emission case of 196 and the dust advection case of 66. The local dust emission case is defined when the calculated dust flux with the two-level (3 m and 15 m high) measured PM<SUB>10</SUB> concentrations by the beta-gauge is upward and the PM<SUB>10</SUB> concentration measured at 3 m high exceeds 100 μg m<SUP>-3</SUP> while all the rest of QCM sampled data are classified as the dust advection case. The results indicate that the spectral mass concentration distribution of the local dust emission case shows a two-modal distribution with one additional mode of the large particle that cannot be resolved by the QCM cascade impactor whereas that of the advection case reveals a three-modal distribution with one additional unresolved large particle mode. The percent spectral mass concentration distribution of the unresolved mode (stage 1) for the local dust emission case is larger than that for the dust advection case. The modal distributions of both cases can be regressed optimally with log-normal distribution functions. The resolved log-normal distribution functions of the mass concentration distribution by the QCM cascade impactor are found to be the particle mean diameter (the standard deviation) of 0.28 (2.07) and 3.15 μm (1.41 μm) for the local emission case and 0.16 (1.51), 0.60 (1.41) and 2.88 μm (1.38 μm) for the advection case. This clearly suggests that the spectral mass concentration shifts toward the larger particle size for the local emission case.

NO_x profile around a signalized intersection of busy roadway

Kim, K.H.,Lee, S.B.,Woo, S.H.,Bae, G.N. Pergamon Press ; Elsevier [distribution] 2014 Atmospheric environment Vol.97 No.-

The NO<SUB>x</SUB> pollution profile around a signalized intersection of a busy roadway was investigated to understand the effect of traffic control on urban air pollution. Traffic flow patterns were classified into three categories of quasi-cruising, a combination of deceleration and acceleration, and a combination of deceleration, idling, and acceleration. The spatial distribution of air pollution levels around an intersection could be represented as a quasi-normal distribution, whose peak height was aggravated by increased emissions due to transient driving patterns. The peak concentration of NO<SUB>x</SUB> around the signalized intersection for the deceleration, idling, and acceleration category was five times higher than that for the quasi-cruising category. Severe levels of NO<SUB>x</SUB> pollution tailed off approximately 400 m from the center of the intersection. Approximately 200-1000 ppb of additional NO<SUB>x</SUB> was observed when traffic was decelerating, idling, and accelerating within the intersection zone, resulting in high exposure levels for pedestrians around the intersection. We propose a fluctuating horizontal distribution of motor vehicle-induced air pollutants as a function of time.

Spatial distribution of polychlorinated biphenyls, organochlorine pesticides, and dechlorane plus in Northeast Asia

Baek, S.Y.,Jurng, J.,Chang, Y.S. Pergamon Press ; Elsevier [distribution] 2013 Atmospheric environment Vol.64 No.-

XAD-2 resin-based passive air samplers (PAS) were deployed for one year at eight cities in Mongolia, China, and South Korea to investigate the spatial distribution of polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), and dechlorane plus (DP). PCB levels were highly correlated with population size and density in China and South Korea. In Mongolia, PCB levels were relatively high considering the low population. In the cases of OCPs and DP, a country-specific distribution was observed. The highest levels of HCHs (hexachlorocyclohexane isomers) and DDTs (dichlorodiphenyl trichloroethane isomers) were detected at sites in China, whereas the highest endosulfan and DP levels were measured at South Korean sites. These results strongly reflected the patterns of use of these chemicals. Mirex, an insecticide never registered in Mongolia and South Korea, was detected at all sampling sites; this is likely to have resulted from long-range transport. Nevertheless, OCPs were generally low in Mongolia. This study confirms that PAS results reflect well the past and current usage of POPs in Northeast Asia.

Influence of a large steel complex on the spatial distribution of volatile polycyclic aromatic hydrocarbons (PAHs) determined by passive air sampling using membrane-enclosed copolymer (MECOP)

Choi, S.-D.,Baek, S.-Y.,Chang, Y.-S. Pergamon Press ; Elsevier [distribution] 2007 Atmospheric environment Vol.41 No.29

Membrane-enclosed copolymer (MECOPs) samplers containing crystalline copolymers of ethylvinylbenzene-divinylbenzene in polyethylene membranes were used to assess the influence of a steel complex on the level and spatial distribution of polycyclic aromatic hydrocarbons (PAHs) in ambient air. MECOPs were deployed at six sites in Pohang, Korea for 37 days (August 9, 2005-September 14, 2005). Fluorene, phenanthrene, anthracene, and fluoranthene were dominant PAHs with the highest contribution of phenanthrene (59%) to the total amount of vapor-phase PAHs. The spatial distribution of total PAHs in the vapor phase ranging from 76 to 1077ngMECOP<SUP>-1</SUP> and air dispersion modeling suggested that the steel complex was the major PAH source in Pohang. It was revealed that the major wind directions rather than the distance from the steel complex were a significant factor affecting the levels of PAHs at the sampling sites. Finally, we tried to convert MECOP concentrations (ngMECOP<SUP>-1</SUP>) to air concentrations (ngm<SUP>-3</SUP>) with the modified sampling rates (m<SUP>3</SUP>day<SUP>-1</SUP>). This study demonstrates again that passive air samplers are useful tools for spatially resolved and time-integrated monitoring of semivolatile organic compounds (SOCs) in ambient air.

Real time measurement of chemical composition of submicrometer aerosols at urban Gwangju in Korea by aerosol mass spectrometer

Park, K.,Park, J.,Lee, S.,Cho, H.j.,Kang, M. Pergamon Press ; Elsevier [distribution] 2012 Atmospheric environment Vol.62 No.-

Size-resolved chemical constituents (organics, sulfate, nitrate, ammonium, and chloride) of nonrefractory submicrometer particles were measured in real time using a quadruple aerosol mass spectrometer (QAMS) at an urban area of Gwangju, Korea in the fall (8/30/2011-9/19/2011) and winter (12/19/2011-12/30/2011). Organics were found to be the most dominant chemical species (~50%) in the total aerosol mass loading. The average mass concentrations of organics were 4.7 +/- 1.8 μg m<SUP>-3</SUP> and 6.3 +/- 1.8 μg m<SUP>-3</SUP> in the fall and winter, respectively. The organics increased in the morning and evening times, and decreased in the afternoon in both the fall and winter, with a more pronounced diurnal pattern observed in the winter. The ratio of m/z 44 to organics and sulfate increased significantly in the afternoon, which is contrary to the behavior of the total organics, suggesting that intense photochemical activity led to the production of oxidized organics and sulfate in the afternoon. The average sulfate concentration was 1.8 μg m<SUP>-3</SUP>, which was the lowest reported in East Asian countries due to there being few SO<SUB>2</SUB> emission sources around the sampling site. The most significant difference in concentrations between the fall and winter was found for nitrate; the concentration was ~4 times higher than in the fall (2.45 μg m<SUP>-3</SUP> versus 0.62 μg m<SUP>-3</SUP>). It was also observed that sulfate, nitrate, and chloride were fully neutralized by the ammonium in the winter, whereas these anions were not fully neutralized in the fall. Size distribution data showed that sulfate had only one D<SUB>va</SUB> peak at 600 +/- 100 nm, regardless of season, and that organics had one peak (600 +/- 100 nm) in the fall and a bimodal distribution (200 +/- 100 nm and 600 +/- 100 nm) in the winter. The absence of the first mode (i.e., D<SUB>va</SUB> ~200 nm) in organics in fall and the higher ratios of m/z 44 to organics in fall (0.10 +/- 0.02) than winter (0.07 +/- 0.01) suggest that oxidized organic species would be more dominant than hydrocarbon-like organics. Air-mass dependent concentrations of species showed that the northwest air mass (i.e., long-range transported from industrial areas in China) and southeast air mass (i.e., transported from industrial area in Korea) were mainly responsible for the high loadings of organics and sulfate.

Aerosol types and radiative forcing estimates over East Asia

Bhawar, R.L.,Lee, W.S.,Rahul, P.R.C. Pergamon Press ; Elsevier [distribution] 2016 Atmospheric environment Vol.141 No.-

Using the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) and MODIS (Moderate Resolution Imaging Spectroradiometer) satellite data sets along with the CSIRO-MK 3.6.0 model simulations, we analyzed the aerosol optical depth (AOD) variability during March-May (MAM), June-August (JJA) along with their annual mean variability over East Asia for the period 2006-2012. The CALIPSO measurements correlated well with the MODIS measurements and the CSIRO-MK 3.6.0 model simulations over the spatial distribution patterns of the aerosols, but CALIPSO underestimated the magnitudes of the AOD. Maximum smoke aerosol loading is observed to occur during JJA, as a result of wind transport from Southern China while dust loading dominated during MAM via the transport from desert region. The vertical distribution profiles revealed that there is uniform distribution of smoke aerosols during both MAM and JJA, only differing at the altitude at which they peak; while the dust aerosols during MAM showed a significant distribution from the surface to 10 km altitude and JJA was marked with lower dust loading at the same altitudes. Both dust and smoke aerosols warm the atmosphere in MAM but due to the absorbing nature of smoke aerosols, they cause considerable cooling at the surface which is double when compared to the dust aerosols. The top of the atmosphere aerosol radiative forcing (ARF) due to smoke and dust aerosols is positive in MAM which indicates warming over East Asia. During MAM a consistent declining trend of the surface ARF due to smoke aerosols persisted over the last three decades as conspicuously evidenced from model analysis; the decline is ~10 W/m<SUP>2</SUP> from 1980 to 2012.

Impact of continuously varied SST on land-sea breezes and ozone concentration over south-western coast of Korea

Lee, S.H.,Lee, H.W.,Kim, Y.K.,Jeon, W.B.,Choi, H.J.,Kim, D.H. Pergamon Press ; Elsevier [distribution] 2011 Atmospheric environment Vol.45 No.35

Several comparison studies including numerical experiments were carried out at the well urbanized Gwangyang Bay region, Korea, to clarify the relationship between the continuously varied SST distribution and meteorology and how that impacts the ozone concentration. The numerical models used in this study were Regional Atmospheric Modeling System (RAMS) and Comprehensive Air quality Model with eXtensions (CAMx) for meteorological and photochemical ozone fields, respectively. Based on buoy observations, the sea surface temperature (SST) had a noticeable influence on the near surface wind field and distribution of photochemical ozone because the mean SST near Gwangyang Bay changed by 2.8 <SUP>o</SUP>C over the five day period. Sea breeze with temporally varied SST was better represented than that estimated without the SST variation. Temporally changed SST distribution and its impact are more crucial factors for estimating the ozone concentration under weak synoptic conditions. And the accuracy of the estimated ozone concentration associated with the time varied SST tends to depend on the distance from the coastline. The acquisition of ocean conditions, including temporal variation in the SST, is indispensible for assessing and predicting the air quality, especially in well urbanized area near the coast.

Improved CMAQ predictions of particulate matter utilizing the satellite-derived aerosol optical depth

Lee, D.,Byun, D.W.,Kim, H.,Ngan, F.,Kim, S.,Lee, C.,Cho, C. Pergamon Press ; Elsevier [distribution] 2011 Atmospheric environment Vol.45 No.22

Regional air quality models such as the Community Multiscale Air Quality (CMAQ) model have been widely used to study and simulate multi-scale air quality issues. Although they are capable of providing high quality atmospheric chemistry profiles through the utilization of high resolution inputs relating meteorology and emissions with chemical reactions, they cannot simulate air quality accurately if other input data are not appropriate and reliable. There have been few studies on the importance of chemical initial conditions (ICs) as it is considered that the impact of concentration fields specified at the beginning of simulation wears off quickly. This paper demonstrates that the significant errors during the early part of the simulation can damage model predictions and conversely if the ICs are prescribed appropriately with available observations, they can compensate for the shortcomings of the air quality prediction system especially when the episode-based emissions inputs representing real-life emission variations such as forest fires as well as the effects of long-range transport events that are not reflected in the basic model inputs. The key hypothesis of the present study is that prediction of aerosols can be improved by the initialization of the aerosol fields with the satellite-derived Aerosol Optical Depth (AOD). We compare the effects of using fine mode and total AOD for the initialization in terms of regional bias characteristics. We found that the impacts of two-step initial conditions adjustments could be substantial in the case of aerosol events such as wildfires, which the present modeling system does not consider during simulation due to the deficiency in the emission inputs. The total AOD case helped to refine PM<SUB>2.5</SUB> predictions over the northwestern area, where wildfire events occurred, for the fire event days improving the correlation coefficient significantly from 0.12 to 0.67. CMAQ predicted PM<SUB>2.5</SUB> concentrations in the fine mode case decreased by 10-50 μg/m<SUP>3</SUP> in large areas of the northwestern region, resulting in more realistic PM<SUB>2.5</SUB> predictions with reduced unusual high peak cells. This study suggest that the use of initial conditions adjusted by total or fine mode AOD can help to improve PM<SUB>2.5</SUB> simulations, even though further refinements of the vertical distribution of aerosols are critically needed.

Airborne cadmium in the major monitoring locations in Korea between 1991 and 2004

Pergamon Press ; Elsevier [distribution] 2007 Atmospheric environment Vol.41 No.21

Air quality monitoring data for cadmium (Cd) collected in 13 cities in Korea over a 14-year period (1991-2004) have been analyzed. In the course of this study, variation of Cd was examined over time and with location to learn about its sources, transport, and removal processes and to help improve air quality control. The results of this study indicate that the spatial distribution of Cd is clearly distinguishable between different cities and that such a pattern is sensitively reflected by such a factor as the level of industrialization. Comparison of the Cd data sets between different cities indicated that its concentration levels observed in highly industrialized cities approached or exceeded 10ngm<SUP>-3</SUP>, while those of urban background cities were found to lie in a narrow range of 1-3ngm<SUP>-3</SUP>. As such, Cd values determined from the polluted areas were notably higher than the relatively clean ones, at least by several times. The Cd data collected from all study sites were also evaluated with respect to temporal behavior. Inspection of seasonal patterns generally showed the occurrences of the highest Cd value during spring (and winter) and the lowest one during summer. When the long-term pattern of Cd was assessed across all study years, the results differed greatly between different cities in relation to their pollution status. Although Cd concentrations tended to decrease rather abruptly in highly industrialized cities, its patterns for most cities were too variable to project a definitive trend. The results of this analysis thus suggest that Cd concentration levels in most urban areas of Korea are fairly comparable with those commonly seen in the urban background areas of western countries. Considering that most urban areas are affected by various pollution sources and that Cd concentrations have been reduced significantly through the years, more deliberate efforts are needed to further control Cd concentrations in the atmosphere.