Mylene G. Cayetano

Time-resolved measurements of PM2.5 carbonaceous aerosols at Gosan, Korea.

ABSTRACT In order to better understand the characteristics of atmospheric carbonaceous aerosol at a background site in Northeast Asia, semicontinuous organic carbon (OC) and elemental carbon (EC), and time-resolved water-soluble organic carbon (WSOC) were measured by a Sunset OC/EC and a PILS-TOC (particle-into-liquid sampler coupled with an online total organic carbon) analyzer, respectively, at the Gosan supersite on Jeju Island, Korea, in the summer (May 28–June 17) and fall (August 24–September 30) of 2009. Hourly average OC concentration varied in the range of approximately 0.87–28.38 μgC m−3, with a mean of 4.07 ± 2.60 μgC m−3, while the hourly average EC concentration ranged approximately from 0.04 to 8.19 μgC m−3, with a mean of 1.35 ± 0.71 μgC m−3, from May 28 to June 17, 2009. During the fall season, OC varied in the approximate range 0.9–9.6 μgC m−3, with a mean of 2.30 ± 0.80 μgC m−3, whereas EC ranged approximately from 0.01 to 5.40 μgC m−3, with a mean of 0.66 ± 0.38 μgC m−3. Average contributions of EC to TC and WSOC to OC were 26.0% ± 9.7% and 20.6% ± 7.4%, and 37.6% ± 23.5% and 57.2% ± 22.2% during summer and fall seasons, respectively. As expected, clear diurnal variation of WSOC/OC was found in summer, varying from 0.22 during the nighttime up to 0.72 during the daytime, mainly due to the photo-oxidation process. In order to investigate the effect of air mass pathway on the characteristics of carbonaceous aerosol, 5-day back-trajectory analysis was conducted using the HYSPLIT model. The air mass pathways were classified into four types: Continental (CC), Marine (M), East Sea (ES) and Korean Peninsula (KP). The highest OC/EC ratio of 3.63 was observed when air mass originated from the Continental area (CC). The lowest OC/EC ratio of 0.79 was measured when air mass originated from the Marine area (M). A high OC concentration was occasionally observed at Gosan due to local biomass burning activities. The contribution of secondary OC to total OC varied approximately between 8.4% and 32.2% and depended on air mass type. IMPLICATIONS Organic material contributes approximately 20–90% of the total fine particulate mass concentration at different sites over the world depending on location and season. Organic carbon consists of hundreds of compounds with a wide range of chemical and optical properties. A better understanding of the chemical characteristics of carbonaceous aerosol influenced by increasing anthropogenic pollution in the downwind regions of the East Asian continent is needed in order to determine their impacts on regional air quality and climate change.

Optical and hygroscopic properties of long-range transported haze plumes observed at Deokjeok Island off the west coast of the Korean Peninsula under the Asian continental outflows

An intensive field campaign was conducted on Deokjeok Island off the west coast of the Korean Peninsula during spring 2009 to characterize the optical and hygroscopic properties of Asian continental outflows. A slightly high wavelength dependence of light absorption coefficient, α of 1.6 ± 0.05 (average ± 1· standard deviation), and a low humidity-dependent light scattering enhancement factor at 80% relative humidity, f(80%) (2.0 ± 0.2), were obtained when air masses originated from the northern part of China (N China), compared to those obtained when air masses originated from the eastern part of China (E China) (α = 1.4 ± 0.1; f(80%) = 2.4 ± 0.2). The relatively high α and low f(80%) during the N China compared to those during the E China were consistent with a relatively high mass ratio of organic aerosol to sum of SO42−, NO3−, and NH4+ during the N China (1.01 ± 0.17) compared to the E China episode (0.25 ± 0.13). This result indicates the importance of organic aerosol on aerosol optical and hygroscopic properties of haze plumes. Single scattering albedo (SSA) of dry particulate matter with a diameter less than or equal to 2.5 µm (PM2.5) (0.92 ± 0.01) and mass scattering efficiency (MSE) of dry PM2.5 at 550 nm wavelength during the E China episode (3.6 ± 0.3 m2 g−1) were higher than those previously obtained at the air mass source regions in China (SSA = ~0.8; MSE = ~3.0 m2 g−1), implying that optical properties of PM2.5 were significantly altered during long-range atmospheric transport.

Oxidative potential of fine ambient particles in various environments

The oxidative potential (OP) and chemical characteristics of fine particles collected from urban, roadside, rural, and industrial sites in Korea during spring, summer, fall, and winter seasons and an urban site in the Philippines during dry and wet seasons were examined. Significant differences in the OP of fine particles among sites and seasons were found. The industrial site yielded the highest OP activity (both mass and volume-normalized OP) among the sites, suggesting the strongest reactive oxygen species (ROS)-generating capability of industry source-dominant PM2.5. Seasonal data show that OP activities increased during the spring and summer possibly due to increased heavy metals caused by dust events and secondary organic aerosols formed by strong photochemical activity, respectively. The strength of the OP association with the chemical components highlights the influence of organic carbon and transition metals on the OP of ambient fine particles. The two OP assays (dithiothreitol (DTT) and electron spin resonance (ESR)) having different ROS-generating mechanisms were found to have different sensitivities to the chemical components facilitating a complementary analysis of the OP of ambient fine particles. Multiple linear regression model equations (OP as a function of chemical components) which were dependent on the sites were derived. A comparison of the daily OP and hazard index (HI) (the ratio of the measured mass concentration to the reference mass concentration of fine particles) suggests that the HI may not be sufficient to accurately estimate the health effects of fine particles, and a direct or indirect measurement of toxicity such as OP should be required in addition to the concentration level.