Gangwoong Lee

Variation of free tropospheric total nitrate at Mauna Loa Observatory, Hawaii

We measured total nitrate (TN) concentrations (defined as nitric acid vapor plus nitrate aerosol) nightly at the Mauna Loa Observatory (MLO) from September 1988 to September 1991. Using three meteorological criteria, (condensation nuclei, wind direction, and dew point) we selected samples that represented the free troposphere. The 3-year mean and median of TN mixing ratios were 113 parts per trillion by volume (pptv) and 93 pptv, respectively. Each year the TN concentrations at MLO during the spring and summer were larger by more than a factor of 2 than those during the fall and winter. The springtime peak TN corresponded to incidents of increased Asian dust over the northern Pacific Ocean. Isentropic back trajectories confirmed that spring air masses with high TN originated over the Asian continent. Back trajectories also indicated that the North American continent was often the source of high TN during the summer. Air mass source regions and flow patterns to MLO were classified into five distinct groups of trajectories by cluster analysis. Despite the different source regions for each of the clusters the distributions of TN were very similar. This suggests that the source region may be less important for determining TN at MLO than such factors as the degree of vertical mixing over source regions, stratospheric injection, and wet removal rates.

Characteristic behavior of peroxyacetyl nitrate (PAN) in Seoul megacity, Korea

We measured the concentrations of peroxyacetyl nitrate (PAN) and other photochemically reactive species, including O3, NO2, and non-methane hydrocarbons (NMHCs), in the Seoul Metropolitan area (SMA) during May through June in 2004 and 2005. PAN was determined using a fast chromatograph with luminol-based chemiluminescence detection. Mixing ratios of PAN ranged from below the detection limit (0.1ppbv) to 10.4ppbv with an average of 0.8ppbv. O3 concentrations ranged from 0 to 141ppbv. The average PAN/O3 ratio of 0.07 was higher than that observed in cities of Europe and North America (0.02) where control strategies have been enforced to reduce hydrocarbon emissions through extensively reformulated gasoline programs. Strong positive correlations between daily PAN and O3 maxima during the day demonstrate that similar photochemical factors controlled the production of these two chemicals. However, relationships between PAN and its precursors, NO2 and NMHCs, suggest that PAN production was more sensitive to NO2 than NMHCs levels whereas O3 production was limited by the overall availability of NMHCs. It is likely that the compositions of NMHCs in SMA were favorable for PAN production because of the low fractions of oxygenated compounds in automobile fuels. PAN maxima were observed around noon, which was 2-3h earlier than the much broader O3 maxima that occurred in the midafternoon. After reaching the maximum, PAN concentrations rapidly dropped within a few hours, which could be largely due to thermal destruction and to limited production under the typically low NO2 levels that occurred in the early afternoon. The heterogeneous destruction of particulate matter could be an additional sink for PAN in SMA.

Effects of changes in environmental conditions on atmospheric mercury exchange: Comparative analysis from a rice paddy field during the two spring periods of 2001 and 2002

It was however found that the soil-air exchange patterns of Hg during the two study periods, although investigated in similar seasonal cycles, contrast to a large extent. Upward emission prevailed in both the frequency and magnitude during the 1st study period, but dry deposition was seen more dominantly in terms of frequency during the 2nd study period. In light of the fact that the occurrence patterns of Asian Dust events differed greatly between the two study periods, the possible role of long-range transport of airborne pollutants (LRTAP) as sources of Hg into the study area has also been examined using information on air mass movement patterns. Because observed differences in Hg flux patterns generally reflect changes in environmental conditions across study periods, the bi-directional exchange patterns of Hg during the two field campaigns were explained in relation to highly diverse environmental conditions that persisted in each study period. INDEX TERMS: 6235 Planetology: Solar System Objects: Mercury; 0312 Atmospheric Composition and Structure: Air/sea constituent fluxes (3339, 4504); 7534 Solar Physics, Astrophysics, and Astronomy: Radio emissions; 0342 Atmospheric Composition and Structure: Middle atmosphere—energy deposition; KEYWORDS: regional background, soil-air exchange, emission, dry deposition, mercury Citation: Kim, K.-H., M.-Y. Kim, J. Kim, and G. Lee, Effects of changes in environmental conditions on atmospheric mercury exchange: Comparative analysis from a rice paddy field during the two spring periods of 2001 and 2002, J. Geophys. Res., 108(D19), 4607, doi:10.1029/2003JD003375, 2003.

Observations of aerosol-bound ionic compositions at Cheju Island, Korea

To investigate the regional cycle of aerosols and their ionic constituents, three field intensive campaigns were conducted during fall and winter of 1997 and spring of 1998. The concentrations of most ionic species were found to decrease significantly across fall, winter, and spring such that the sum for all cation (and anion) species of each season is computed as: 193 > 96 > 73.7 nequiv m(-3) (and 240 > 104 > 51.5 nequiv m(-3)). To examine the fundamental characteristics of aerosol compositions in the study area, we conducted correlation analysis in various manners. The results indicated that the concentrations of major ionic species were strongly affected by some meteorological parameters including wind speed. It was also seen that relative strengths of correlations between important parameters (e.g., between wind speed and most of major inorganic species) maintain close relationships with the factors associated with the air mass origin. In addition, the results of factor analysis indicated the existence of at least three major sources in the study area which include: sea-salt aerosol, secondary aerosol, and organic aerosol component. The springtime occurrence of unexpectedly low concentrations of most ionic constituents is found to sensitively reflect the influence of the inflow of southeasterly winds that prevailed during spring, while it is not common for that season of the year. Because most of those changes are closely tied with the variabilities in the regional circulation patterns for each measurement period, assessment of the ionic composition in concert with the temporal variations of meteorological conditions provided valuable insights into the source signals of different air masses that passed by the study area.

Field-measured uptake rates of PCDDs/Fs and dl-PCBs using PUF-disk passive air samplers in Gyeonggi-do, South Korea

The collection of 2,3,7,8-substituted polychlorinated dibenzo-ρ-dioxins and dibenzo furans (PCDDs/Fs) and dioxin-like polychlorinated biphenyls (dl-PCBs) using a polyurethane form (PUF)-disk passive air sampler (PAS) was investigated in urban-residential and industrial areas. This was performed to assess the feasibility of using this method as an alternative to an active air sampler (AAS). The PUF-disk PAS was exposed to ambient air over a period of 37-370 and 57-173 days in urban and industrial areas, respectively, together with AASs. The sum of total toxic equivalent quantity (TEQ) ΣPCDDs/Fs and Σdl-PCB was typically high in the industrial area, with values within the range 0.171-0.635 pg-TEQ/m(3), and 0.037-0.300 pg-TEQ/m(3) in the urban-residential area. To derive the time-weighted average (TWA) concentration from the PAS data accurately, it was estimated that the PAS deployed for less than 80 days was adequate to maintain linear accumulation conditions. PCDDs/Fs are mainly particle bound and showed low average uptake rates of 1.4m(3)d(-1), while dl-PCBs were slightly higher with 2.0m(3)d(-1) because of its high vapor pressure. Most of the congener concentrations measured using the PAS and AAS were within a factor of two, indicating that PASs can be used to monitor spatial and temporal variations in the concentrations of persistent organic pollutants (POPs) in the atmosphere.

Dimethylsulfide and its oxidation products in coastal atmospheres of Cheju Island.

The concentrations of dimethylsulfide (DMS) in air and its oxidation products in aerosols were measured from the coastal atmospheres of Cheju Island, Korea, during three exploratory field experiments conducted over September 1997 through April 1998. According to our measurements, there were large fluctuations in the distribution of DMS and relevant species in the coastal atmospheres; the magnitude of variations was significant both within each measurement period and across different measurement periods. The mean mixing ratios of atmospheric DMS from the whole data sets were found within the range of 19 to 1140 pptv (n=84) with the grand mean value of 100 pptv. Like DMS, large variations in the data distribution were consistently seen from other species investigated concurrently. The concentrations of aerosol ions including non-seasalt sulfate (NSSS), seasalt sulfate (SSS), and methane sulfonate (MSA) spanned over two orders of magnitude such as 0.24-88 (mean 32), 0.08-17.2 (mean 3.70), and 0.01-0.78 (mean 0.16) nmol m(-3), respectively. The molar ratios of those ions were measured as: (1) NSSS/SSS in 1.26-95 (mean 44); (2) MSA/NSSS in 0.0002-0.063 (mean 0.009); and (3) NSSS/NO(3) in 0.21-9.5 (mean 2.35). Examinations of our measurement data indicated that the concentrations of DMS and relevant ions varied significantly across day/night periods and across different seasons. It was also seen that there are strong differences in seasonal distribution patterns between fall, winter, and spring. Detailed analysis of the data sets revealed that changes in their distribution patterns were in strong compliance with changes in meteorological conditions. Especially, large fluctuations in magnitudes and amplitudes of springtime DMS concentrations were coinciding with the intrusion of southeasterly winds, suggesting the possibility that the DMS-rich air masses were brought into the study area from the productive waters of the southeast coastal area of Cheju. Similarly to the case of DMS, the occurrence of unusual wind patterns during spring contributed to changes in the content and composition of aerosol ions. Although the introduction of southeasterly winds during spring helped maintain high DMS and MSA levels, the concentrations of aerosol ions dropped significantly because of depositional loss during the passage of air mass over land area. According to the procedures of Wylie and De Mora, we reached the conclusion that the magnitude of annual DMS emissions in the western Korean sea were in the range of 5 to 18 Gg S.

Vertical variability of seawater DMS in the South Pacific Ocean and its implication for atmospheric and surface seawater DMS

Shipboard measurements of atmospheric dimethylsulfide (DMS) and sea surface water DMS were performed aboard the R/V Onnuri across the South Pacific from Santiago, Chile to Fiji in February 2000. Hydrographic profiles of DMS, dissolved dimethylsulfoniopropionate (DMSP(d)), and particulate DMSP(p) in the upper 200m were obtained at 16 stations along the track. Atmospheric and sea surface water DMS concentrations ranged from 3 to 442pptv and from 0.1 to 19.9nM, respectively; the mean values of 61pptv and 2.1nM, respectively, were comparable to those from previous studies in the South Pacific. The South Pacific Gyre was distinguished by longitudinal-vertical distributions of DMS, DMSP(d), and DMSP(p), which was thought to be associated with the characteristic modification of biological activities that occurs mainly due to significant change in water temperature. The averaged DMS maximum appeared at 40m depth, whereas DMSP(p) and DMSP(d) maxima coincided with that of dissolved oxygen content at 60-80m. The sea-to-air fluxes of DMS were estimated to be 0.4-11.3micromold(-1)m(-2) (mean=2.8micromold(-1)m(-2)). A fairly good correlation between atmospheric DMS and sea-to-air DMS flux indicated that atmospheric DMS concentration was more sensitive to change in physical parameters than its photochemical removal process or surface seawater DMS concentrations.

Concentration gradients and dry deposition of nitric acid vapor at the Mauna Loa Observatory, Hawaii

From August 14 to September 5, 1991, we measured the mixing ratio of nitric acid vapor and several aerosol species (nitrate, sulfate, ammonium and sodium) at three heights (2 m, 10 m and 30 m) at the Mauna Loa Observatory. Well-defined logarithmic gradients of temperature and HNO3 vapor were measured throughout the experiment, indicating rapid HNO3 vapor deposition to the ground. Measured dry deposition velocities for HNO3 vapor ranged from 0.27 to 4 cm s−1. The collection efficiency for HNO3 vapor varied with sampler location and orientation on the sampling tower, due to concentration depletion by the tower or the sampler itself. We found that our long-term samplers at 8 m may underestimate free tropospheric HNO3 mixing ratios by about 20% due to dry deposition.

Characteristics of atmospheric hydrogen peroxide variations in Seoul megacity during 2002–2004

Atmospheric hydrogen peroxides (H(2)O(2)) and methyl hydroperoxide (CH(3)OOH) were measured in Seoul, the capital of South Korea. Experiments were performed for several days almost every month from January 2002 to April 2004. Gaseous hydroperoxide was collected in aqueous solution and determined by HPLC-fluorescence method. In general, the higher levels of H(2)O(2) were found in warm and humid air with high ozone concentrations, but lower concentrations of SO(2), NO(2), CO and PM(10). For two-year measurements, seasonal factor was the most dominant and the concentrations of H(2)O(2) were highest in summer, for which the median, mean, and upper 90% values were 0.53 ppbv, 0.81 ppbv, and 1.61 ppbv, respectively. In highly polluted metropolitan Seoul, the photochemical activity controlling H(2)O(2) variations was seemingly more sensitive to meteorological conditions than the level of chemical pollutants. It was mainly due to high emissions of pollutants, particularly NOx, which was demonstrated by the occasional occurrence of CH(3)OOH.

Concentration and Gas-particle Partition of PCDDs/Fs and dl-PCBs in the Ambient Air of Ansan Area

After establishment of Banwol industrial complex in 1987, Ansan city becomes the largest industrial sector development in Gyeonggi-do, Korea. As the population and industrial activity grow over this region, toxic air pollutants, particularly POPs (Persistent Organic Pollutants) from various emission sources have been major public concerns. Air samples for POPs monitoring were collected at the industrial sites (), residential sites (, ), commercial site (C), and rural/remote site (D) of the area of Ansan during 2008 with a prolonged industrial sampling site from 2001 to 2008. All samples were analysed for 2,3,7,8 substituted-polychlorinated dibenzo-p-dioxin and dibenzofurans (PCDD/Fs) and dioxin like polychlorinatd diphenyls (dl-PCBs). In site , a steady decline of their concentrations from 2003 to 2008 was observed due to the reinforced emission guideline from waste incinerators. The average concentration of the PCDD/Fs and dl-PCBs ranged between 0.118 pg-TEQ/ (rural/remote site D) and 0.532 pg-TEQ/ (industrial area ). These level were generally consistent with previous studies in Gyeonggi-do, while higher than other places. Most of PCDD/Fs congener were partitioned into particle phase, whereas dl-PCBs were partitioned into gas phase. The logarithm of gas-particle partition coefficient of dl-PCBs and PCDD/Fs were well correlated with sub-cooled liquid vapor pressure . The slope of log versus log for PCDD/Fs (-1.22) and dl-PCBs (-1.02) in industrial area () were high compared to other residential/commercial area. It suggests that this area was likely influenced by the direct emission source of PCDD/Fs and dl-PCBs. To simulate the partition of PCDD/Fs and dl-PCBs between gas and particle phase, Junge-Pankow model (-base) and model were applied. It was found that J-P model was more suitable than the model in this study.