Contribution of liquid water content enhancing aqueous phase reaction forming ambient particulate nitrosamines.

Contribution of liquid water content (LWC) to the levels of the carcinogenic particulate nitro(so) compounds and the chemistry affecting LWC were investigated based on the observation of seven nitrosamines and two nitramines in rural (Seosan) and urban (Seoul) area in South Korea during October 2019 and a model simulation. The concentrations of both the total nitrosamines and nitramines were higher in Seosan (12.48 ± 16.12 ng/m3 and 0.65 ± 0.71 ng/m3, respectively) than Seoul (7.41 ± 13.59 ng/m3 and 0.24 ± 0.15 ng/m3, respectively). The estimated LWC using a thermodynamic model in Seosan (12.92 ± 9.77 µg/m3) was higher than that in Seoul (6.20 ± 5.35 µg/m3) mainly due to higher relative humidity (75 ± 9% (Seosan); 62 ± 10% (Seoul)) and higher concentrations of free ammonia (0.13 ± 0.09 µmol/m3 (Seosan); 0.08 ± 0.01 µmol/m3 (Seoul)) and total nitric acid (0.09 ± 0.07 µmol/m3 (Seosan); 0.04 ± 0.02 µmol/m3 (Seoul)) in Seosan while neither fog nor rain occurred during the sampling period. The relatively high concentrations of the particulate nitrosamines (>30 ng/m3) only observed probably due to the higher LWC (>10 µg/m3) in Seosan. It implies that aqueous phase reactions involving NO2 and/or uptake from the gas phase enhanced by LWC could be promoted in Seosan. Strong correlation between the concentrations of nitrosodi-methylamine (NDMA), an example of nitrosamines, simulated by a kinetic box model including the aqueous phase reactions and the measured concentration of NDMA in Seosan (R = 0.77; 0.37 (Seoul)) indicates that the aqueous phase reactions dominantly enhanced the NDMA concentrations in Seosan. On the other hand, it is estimated that the formation of nitrosamines by aqueous phase reaction was not significant due to the relatively lower LWC in Seoul compared to that in Seosan. Furthermore, it is presumed that nitramines are mostly emitted from the primary emission sources. This study implies that the concentration of the particulate nitrosamines can be promoted by aqueous phase reaction enhanced by LWC.

Effects of combustion condition and biomass type on the light absorption of fine organic aerosols from fresh biomass burning emissions over Korea.

In this study, the light absorption properties of fine organic aerosols from the burning emissions of four biomass materials were examined using UV-spectrophotometry and Aethalometer-measurements, respectively. For wood chips and palm trees, the burning experiments were carried out with different combustion temperatures (200, 250, and 300 οC) in an adjustable, electrically heated combustor. The light absorptions of water and methanol extracts of aerosols, and smoke particles showed strong spectral dependence on the burning emissions of all biomass materials. However, the burning aerosols of wood chips showed stronger absorption than those of the other biomass burning (BB) emissions. For the burning aerosols of wood chips and palm trees, organic carbon/elemental carbon (OC/EC) decreased as the combustion temperature increased from 200 to 300 °C. Absorption Ångström exponent (AAE) values tended to decrease when combustion temperature increased for smoke aerosols and methanol extracts in smoke samples. The mass absorption efficiency at 365 nm (MAE365, m2 g-1∙C-1) of water- and methanol-extractable OC fractions was highest in wood chip burning smoke samples. MAE365 values of methanol extracts for rice straw, pine needles, wood chips, and palm trees burning emission samples were 1.35, 0.92, 2.36-3.37, and 0.86-1.42, respectively. For wood chip and palm tree burning emissions, AAE320-430nm values of methanol extracts were strongly correlated with OC/EC (i.e., combustion temperature) with slopes of 0.11 (p < 0.001) and 0.02 (p < 0.001), and R2 values of 0.87 and 0.74, respectively. Moreover, a linear regression between MAE365 of methanol extractable OC and OC/EC showed slopes of -0.05 (p < 0.001) and -0.004 (p < 0.001) and R2 of 0.72 and 0.74, respectively. The results of this study clearly demonstrate that burning condition and biomass type influence the light absorption properties of organic aerosols from BB emissions.

Qualitative assessment to determine internal and external factors influencing the origin of styrene oligomers pollution by polystyrene plastic in coastal marine environments.

The objective of this study is to investigate the qualitative contribution of internal and external factors of the area contaminated by polystyrene (PS) in coastal marine environments. This study is based on the extensive results of monitoring the styrene oligomers (SOs) present in sand and seawater samples along various coastlines of the Pacific Ocean. Here, anthropogenic SOs is derived from PS during manufacture and use, and can provide clues about the origin of SOs by PS pollution. The monitoring results showed that, if the concentration of SOs in water is higher than those concentrations in beach sand, this area could be affected by PS plastic caused by an external factor. On the other hand, if the concentration of SOs is higher in the beach sand, the region can be mainly influenced by PS plastic derived from its own area. Unlike the case of an external factor, in this case (internal influence), it is possible to take policy measures of the area itself for the PS plastic problem. Thus, this study is motivated by the need of policy measures to establish a specific alternative to the problems of PS plastic pollution in ocean environments.

Synergetic analysis of springtime air pollution episodes over Gwangju, Korea.

The characteristics of springtime aerosols, including their optical and microphysical properties, were analyzed for the months of March to May of 2009 in Gwangju (35.23°N, 126.84°E), Korea. A high Light Detection and Ranging (LIDAR)-derived aerosol depolarization ratio (δ) of 0.25±0.04 was determined on dust particles during the observation period. The Ångström exponent values of the 440-870nm wavelength pair (Å440-870) and single-scattering albedo at 675nm (Ω675) measured by a CIMEL sun/sky radiometer were 0.77±0.19 and 0.95±0.01, respectively. The elevated dust layers reached a maximum elevation of 4km above sea level. Anthropogenic/smoke particles that originated from highly populated/industrialized regions could be distinguished by their relatively smaller particle size (Å440-870 ranged between 1.33 and 1.36) and higher light-absorbing (Ω675 of 0.92±0.01) characteristics. These aerosols are mostly distributed at altitudes <1.2km. The root-mean-square deviation (RMSD) between the aerosol optical depth (AOD, τ) derived from LIDAR (τLIDAR) and from the CIMEL sun/sky radiometer (τCIMEL) varied with respect to the surface PM10 concentration. The RMSD between τLIDAR and τCIMEL was as low as 13% under lower PM10 concentration levels (<100µg/m3). In contrast, the RMSD between τLIDAR and τCIMEL increased three times (~31%) under high surface PM10 concentration levels (>100µg/m3). These results suggest that the accuracy of τLIDAR is influenced by specific atmospheric conditions, regardless of its uncertainty.

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.

Source contributions and potential source regions of size-resolved water-soluble organic carbon measured at an urban site over one year.

In this study, 24 h size-segregated particulate matter (PM) samples were collected between September 2012 and August 2013 at an urban site in Korea to investigate seasonal mass size distributions of PM and its water-soluble components as well as to infer the possible sources of size-resolved water-soluble organic carbon (WSOC) using a positive matrix factorization (PMF) model. The potential source contribution function (PSCF) was also computed to identify the possible source regions of size-resolved WSOC. The seasonal average contribution of water-soluble organic matter to PM1.8 was in the range from 12.7 to 19.7%, but higher (21.0%) and lower contributions (8.9%) were observed during a severe haze event and an Asian dust event, respectively. The seasonal mass size distribution of WSOC had a dominant droplet mode peaking at 0.55 µm and a minor coarse mode peaking at 3.1 µm. The droplet mode WSOC was found to strongly correlate with oxalate, SO42-, NO3-, and K+, suggesting that in-cloud processes and biomass burning emissions are important sources of droplet mode WSOC. This finding was verified by the results obtained using PMF models. Secondary organic aerosols (oxalate + SO42- + NO3-) and biomass burning were the most important contributors (70.3%) to condensation mode WSOC. In the droplet mode, in-cloud processes and secondary NO3- (+biomass burning) were important sources of WSOC, contributing on average 46.4 and 25.9% to the WSOC, respectively. In the coarse mode, soil dust and secondary processes contributed 52.5 and 42.5% to the WSOC, respectively. The PMF analyses and PSCF maps of WSOC, SO42-, and K+ indicate that condensation mode WSOC was mostly influenced by the secondary organic aerosols and biomass burning from both local and long-range transported pollutants, while droplet mode WSOC was primarily the result of atmospheric processing during the long range transport of biogenic and anthropogenic pollutants from the eastern regions of China.

Size distribution and sources of humic-like substances in particulate matter at an urban site during winter.

This study investigates the size distribution and possible sources of humic-like substances (HULIS) in ambient aerosol particles collected at an urban site in Gwangju, Korea during the winter of 2015. A total of 10 sets of size-segregated aerosol samples were collected using a 10-stage Micro-Orifice Uniform Deposit Impactor (MOUDI), and the samples were analyzed to determine the mass as well as the presence of ionic species (Na(+), NH4(+), K(+), Ca(2+), Mg(2+), Cl(-), NO3(-), and SO4(2-)), water-soluble organic carbon (WSOC) and HULIS. The separation and quantification of the size-resolved HULIS components from the MOUDI samples was accomplished using a Hydrophilic-Lipophilic Balanced (HLB) solid phase extraction method and a total organic carbon analyzer, respectively. The entire sampling period was divided into two periods: non-Asian dust (NAD) and Asian dust (AD) periods. The contributions of water-soluble organic mass (WSOM = 1.9 × WSOC) and HULIS (=1.9 × HULIS-C) to fine particles (PM1.8) were approximately two times higher in the NAD samples (23.2 and 8.0%) than in the AD samples (12.8 and 4.2%). However, the HULIS-C/WSOC ratio in PM1.8 showed little difference between the NAD (0.35 ± 0.07) and AD (0.35 ± 0.05) samples. The HULIS exhibited a uni-modal size distribution (@0.55 µm) during NAD and a bimodal distribution (@0.32 and 1.8 µm) during AD, which was quite similar to the mass size distributions of particulate matter, WSOC, NO3(-), SO4(2-), and NH4(+) in both the NAD and AD samples. The size distribution characteristics and the results of the correlation analyses indicate that the sources of HULIS varied according to the particle size. In the fine mode (≤1.8 µm), the HULIS composition during the NAD period was strongly associated with secondary organic aerosol (SOA) formation processes similar to those of secondary ionic species (cloud processing and/or heterogeneous reactions) and primary emissions during the biomass burning period, and during the AD period, it was only associated with SOA formation. In the coarse mode (3.1-10 µm), it was difficult to identify the HULIS sources during the NAD period, and during the AD period, the HULIS was most likely associated with soil-related particles [Ca(NO3]2 and CaSO4) and/or sea-salt particles (NaNO3 and Na2SO4).

Source identification of water-soluble organic aerosols at a roadway site using a positive matrix factorization analysis.

Daily PM2.5 measurements were carried out at a local roadway every sixth day from May 2011 to August 2013 to obtain seasonal quantitative information on the primary and secondary sources of two water-soluble organic carbon (WSOC) fractions. Filter samples were analyzed for OC, elemental carbon (EC), WSOC, hydrophilic and hydrophobic WSOC fractions (WSOC(HPI) and WSOC(HPO)), and ionic species. An XAD solid phase extraction method and a total organic carbon analyzer were used to isolate the two WSOC fractions and determine their amounts, respectively. The WSOC/OC and WSOC(HPI)/WSOC ratios were 0.62±0.13 and 0.47±0.14, respectively. Similar seasonal profiles in EC, OC, and WSOC concentrations were observed, with higher concentrations occurring in the cold season and lower concentrations in the warm season. However, opposite results were obtained in WSOC/OC and WSOC(HPI)/WSOC ratios, with the higher in the warm season and the lower in the cold season. Correlation analyses indicated that two WSOC fractions in winter were likely attributed to secondary formation processes, biomass burning (BB), and traffic emissions, while WSOC(HPI) observed in other seasons were associated with secondary formation processes similar to those of oxalate and secondary inorganic species. A positive matrix factorization (PMF) model was employed to investigate the sources of two WSOC fractions. PMF indicated that concentrations of WSOC fractions were affected by five sources: secondary NO3(-) related, secondary SO4(2-) and oxalate related, traffic emissions, BB emissions, and sea-salt. Throughout the study period, secondary organic aerosols were estimated to be the most dominant contributor of WSOC fractions, with higher contributions occurring in the warm seasons. The contribution of secondary aerosol formation processes (NO3(-) related+SO4(2-) and oxalate related) to WSOC(HPI) and WSOC(HPO) was on an average 56.2% (45.0-73.8%) and 47.7% (39.6-52.1%), respectively. The seasonal average contribution of WSOC(HPI) and WSOC(HPO) attributed to BB was 19.0% (14.3-25.3%) and 14.8% (7.2-19.5%), respectively, with higher fractions occurring in the fall and winter. Traffic sources contributed to WSOC(HPI) and WSOC(HPO) from 4.2 to 21.0% (an average of 11.6%) and from 7.9 to 32.3% (an average of 19.9%), respectively, with higher fractions in the fall and winter compared with the other seasons. During the study period, for an episode associated with high local O3 level (~110 ppbv) and high WSOC(HPI)/WSOC (0.80), secondary formation processes contributed 67.1% to WSOCHPI, and 72.6% to WSOC(HPO), respectively. However, for an episode associated with local and severe regional haze pollutions, contributions of secondary formation processes to WSOC fractions were observed to be low (32.4-43.1%), while traffic and BB emissions contributed 16.8% and 24.3% to WSOC(HPI), respectively, and 18.3% and 18.7% to WSOC(HPO), respectively. The PMF results suggest that the contribution of traffic emissions to concentrations of two WSOC fractions cannot be neglected at the studied roadway site.

Difference in production routes of water-soluble organic carbon in PM2.5 observed during non-biomass and biomass burning periods in Gwangju, Korea.

4 h integrated PM2.5 samples were collected from an urban site of Gwangju, Korea, for five days and analyzed for organic carbon and elemental carbon (OC and EC), total water-soluble OC (WSOC), hydrophilic and hydrophobic WSOC fractions (WSOCHPI and WSOCHPO), oxalate, and inorganic ionic species (sodium (Na(+)), ammonium (NH4(+)), potassium (K(+)), calcium (Ca(2+)), magnesium (Mg(2+)), chloride (Cl(-)), nitrate (NO3(-)), and sulfate (SO4(2-))) to investigate the possible sources of water-soluble organic aerosols. Two types of sampling periods were classified according to the regression relationship between black carbon (BC) concentrations measured at wavelengths of 370 nm (BC370nm) and 880 nm (BC880nm) using an aethalometer; the first period was traffic emission influence ("non-biomass burning (BB) period") and the second was biomass burning influence ("BB period"). The slope of the regression equation (BC370nm/BC880nm) was 0.95 for the non-BB period and 1.29 for the BB period. However, no noticeable difference in the WSOC/OC ratio, which can be used to infer the extent of secondary organic aerosol (SOA) formation, was found between the non-BB (0.61, range = 0.43-0.75) and BB (0.61, range = 0.52-0.68) periods, due to significant contribution of primary BB emissions to the WSOC. The concentrations of OC, WSOC and K(+), which were used as the BB emission markers, were 15.7 µg C m(-3) (11.5-24.3), 9.4 µg C m(-3) (7.0-12.7), and 1.2 µg m(-3) (0.6-2.7), respectively, during the BB period, and these results were approximately 1.7, 1.7, and 3.9 times higher than those during the non-BB period. During the non-BB period, good correlations among WSOC, SO4(2-) and oxalate, and poor correlations among WSOC, EC, and K(+) suggest that SOA is probably an important source of WSOC (and WSOCHPI) concentration. For the WSOC fractions, better correlations among WSOCHPI, oxalate (R(2) = 0.52), and SO4(2-) (R(2) = 0.57) were found than among WSOCHPO, oxalate (R(2) = 0.23), and SO4(2-) (R(2) = 0.20), suggesting that a significant proportion of the WSOCHPI fraction of OC could be produced through processes (gas-phase and heterogeneous oxidations) such as SOA formation. However, during the BB period, the BB emission source accounted for the high correlations between total WSOC (and WSOC fractions) and other relevant atmospheric parameters (EC, Na(+), Cl(-), K(+), and oxalate), with higher correlations in WSOCHPI than in WSOCHPO. These results suggest a significant contribution of BB emissions to WSOC.

A study of bactericidal effect and optimization of pathogenic bacteria using TiO2 photocatalyst.

The photocatalytic degradation of Salmonella choleraesuis subsp. and Vibrio parahaemolyticus in water by TiO2 catalysts was investigated in a batch reactor. After 30 min of irradiation with UV light in the presence of 1 mg/ml of TiO2, death ratio of S. choleraesuis subsp. and V. parahaemolyticus was 60% and 83%, respectively. And complete killing of the cells was achieved after 3 h of illumination in the presence of TiO2. We established the response surface methodology to investigate the effect of principal parameters on the pathogenic bacteria sterilization such as TiO2 concentration, pH and temperature. By applying response surface analysis to the bactericidal effect of S. almonella choleraesuis subsp. and V. parahaemolyticus, we found that the cell death ratio was influenced significantly by the first order term of TiO2 concentration.