Numerical simulation of atmospheric CO2 concentration and flux over the Korean Peninsula using WRF-VPRM model during Korus-AQ 2016 campaign.

We conducted regional scale CO2 simulations using the Weather Research and Forecasting model (WRF) coupled with the Vegetation Photosynthesis and Respiration Model (VPRM). We contrasted simulated concentrations with column, ground and aircraft observations during the Korea-United States Air Quality (KORUS-AQ) 2016 field campaign. Overall, WRF-VPRM slightly underestimates CO2 concentrations at ground and column monitoring sites, but it significantly underestimates at an inland tower measurement site, especially within the stable (nocturnal) boundary layer in nighttime. The model successfully captures the airborne vertical profiles but showed a large offset within the planetary boundary layer (PBL) in the areas surrounding Seoul and around the Taeahn point source emissions in the west coastal area of the Korean Peninsula. A case study flight intended to capture Chinese influence observed no clear signals of long-range transport of CO2, due mainly to the much larger magnitude of background CO2 concentrations. The calculated Net Ecosystem Exchange (NEE) with flux measurements at a tower site in the South Korean Peninsula has also been evaluated comparing with CO2 flux measurements at a flux tower site, resulting in the underestimation by less than a factor of 1.

Identification of chemical fingerprints in long-range transport of burning induced upper tropospheric ozone from Colorado to the North Atlantic Ocean.

This study investigates a significant biomass burning (BB) event occurred in Colorado of the United States in 2012 using the Community Multi-scale Air Quality (CMAQ) model. The simulation reasonably reproduced the significantly high upper tropospheric O3 concentrations (up to 145ppb) caused by BB emissions. We find the BB-induced O3 was primarily affected by chemical reactions and dispersion during its transport. In the early period of transport, high NOx and VOCs emissions caused O3 production due to reactions with the peroxide and hydroxyl radicals, HO2 and OH. Here, NOx played a key role in O3 formation in the BB plume. The results indicated that HO2 in the BB plume primarily came from formaldehyde (HCHO+hv=2HO2+CO), a secondary alkoxy radical (ROR=HO2). CO played an important role in the production of recycled HO2 (OH+CO=HO2) because of its abundance in the BB plume. The chemically produced HO2 was largely converted to OH by the reactions with NO (HO2+NO=OH+NO2) from BB emissions. This is in contrast to the surface, where HO2 and OH are strongly affected by VOC and HONO, respectively. In the late stages of transport, the O3 concentration was primarily controlled by dispersion. It stayed longer in the upper troposphere compared to the surface due to sustained depletion of NOx. Sensitivity analysis results support that O3 in the BB plume is significantly more sensitive to NOx than VOCs.

Impact of future urban growth on regional climate changes in the Seoul Metropolitan Area, Korea.

The influence of changes in future urban growth (e.g., land use changes) on the future climate variability in the Seoul metropolitan area (SMA), Korea was evaluated using the WRF model and an urban growth model (SLEUTH). The land use changes in the study area were simulated using the SLEUTH model under three different urban growth scenarios: (1) current development trends scenario (SC 1), (2) managed development scenario (SC 2) and (3) ecological development scenario (SC 3). The maximum difference in the ratio of urban growth between SC 1 and SC 3 (SC 1 - SC 3) for 50years (2000-2050) was approximately 6.72%, leading to the largest differences (0.01°C and 0.03ms(-1), respectively) in the mean air temperature at 2m (T2) and wind speed at 10m (WS10). From WRF-SLEUTH modeling, the effects of future urban growth (or future land use changes) in the SMA are expected to result in increases in the spatial mean T2 and WS10 of up to 1.15°C and 0.03ms(-1), respectively, possibly due to thermal circulation caused by the thermal differences between urban and rural regions.

Identification and interpretation of representative ozone distributions in association with the sea breeze from different synoptic winds over the coastal urban area in Korea.

To aid the studies of long-term impact assessment of cumulative ozone (O3) exposures, the representative 8-hr O3 pollution patterns have been identified over the Greater Seoul Area (GSA) in Korea. Principal component analysis and two-stage clustering techniques were used to identify the representative O3 patterns, and numerical and observational analyses were also used to interpret the identified horizontal distribution patterns. The results yielded three major O3 distribution patterns, and each of the three patterns was found to have strong correlations with local and synoptic meteorological conditions over the GSA. For example, pattern 1, accounting for 46% of O3 concentration distributions, mostly occurred under relatively weak westerly synoptic winds. The predominant features of this pattern were infrequent high O3 levels but a distinct gradient of O3 concentration from the western coastal area to the eastern inland area that was mainly induced by the local sea breeze. Pattern 2, accounting for 31% of O3 concentration distributions, was found with higher O3 levels in the western coastal area but lower in the eastern inland area. This is due to the modified sea breeze under the relatively stronger easterly opposing synoptic wind, affecting the high O3 occurrence in the western coastal area only. However, pattern 3, accounting for 21% of O3 concentration distributions, showed significantly higher O3 concentrations over the whole GSA mainly due to the retarded and slow-moving sea-breeze front under the weak opposing synoptic flow. Modeling study also indicated that local and synoptic meteorological processes play a major role in determining the high O3 concentration distribution patterns over the GSA.

Characteristics of Asian dust transport based on synoptic meteorological analysis over Korea.

Classification of synoptic patterns and their correlation with dust events over East Asia were performed by means of cluster analysis. The average linkage and K-means clustering techniques were used to identify two major weather types during Asian dust events (ADEs; total 26 ADEs with 47 dusty days) of six spring seasons from 1996 to 2001. The first weather type mainly influenced neighboring Asian countries and frequently occurred with ADEs (approximately 23% of ADE cases). It mostly occurred under a surface high (low)-pressure system over the west (east) of the Korean peninsula coupled with an upper-level trough and cutoff low passage over the center of the Korean peninsula. It showed strong advection in the middle/ upper troposphere with both a high aerosol index and enhanced coarse particulate matter (PM) loading over Korea. In contrast, the second weather type was mostly associated with long distance or continental-scale transport and occurred less frequently with ADEs (approximately 15%). It appeared with an upper-level trough and a cutoff low vertically connected with a surface low system that was formed by a strong cyclonic vortex over the north of the Korean peninsula. There were weak advection, low aerosol index, and low coarse PM concentration over the Korean peninsula during the second weather type. In addition, it was found to be mostly associated with the trans-Pacific transport of Asian dust to the western coast of North America.

Comparison of outdoor and indoor mobile source-related volatile organic compounds between low- and high-floor apartments.

The current study examined the hypothesis that there may be vertical variation in mobile source-related volatile organic compound (VOC) concentrations in high-rise apartment buildings. One hundred twelve homes in 56 high-rise apartment buildings with 10 or more stories participated in the study. Both the outdoor and the indoor air concentrations of three VOCs [methyl-tertiary butyl ether (MTBE), benzene, and toluene] were significantly higher for the low-floor apartments than for the high-floor apartments (P < 0.05). The median outdoor concentrations were 5.4, 6.8, and 29.1 microgram/m3, respectively, for the low-floor apartments, yet 4.4, 4.3, and 21.9 microgram/m3, respectively, for the high-floor apartments. Meanwhile, the median indoor concentrations were 6.3, 9.4, and 44.8 microgram/m3, respectively, for the low-floor apartments, yet 5.1, 7.6, and 38.8 microgram/m3, respectively, for the high-floor apartments. These findings indicate that residents of low-floor apartments are exposed to elevated residential levels of mobile source-related VOCs compared to high-floor apartment residents. The indoor concentrations of the target VOCs, except for MTBE, were significantly higher than the outdoor air concentrations for both the low and high floors (P < 0.05). Plus, the outdoor and indoor VOC concentrations were significantly different between the daytime and nighttime data sets for both low- and high-floor apartments, with a P value of less than or close to 0.05.