Search

North Korea's air quality is poorly understood due to a lack of reliable data. Here, we analyzed urban- to national-scale air quality changes in North Korea using multi-year satellite observations. Pyongyang, Nampo, Pukchang, and Munchon were identified as pollution hotspots. On a national scale, we found that North Korea experienced 6.7, 17.8, and 20.6 times greater amounts of nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO) per unit primary energy supply (PES) than South Korea from 2005 to 2018. Besides, North Korea had a 24.3 times larger aerosol optical depth (AOD) per PES than South Korea from 2011 to 2018. Severe CO and aerosol pollution is aligned with extensive biofuel combustion. High SO2 pollution corresponds with the strong coal dependence of the industry. The change rates of the national average columns for NO2, SO2, and CO were + 3.6, -4.4, and -0.4 % yr-1, respectively. The AOD change rate was -4.8 % yr-1. Overall decreasing trends, except for NO2, are likely due to a decline in coal-fired PES. Positive NO2 trends are consistent with increasing industrial activities. Each pollutant showed consistent patterns of linear trends, even after correcting the influence of transboundary pollution. Flue gas control and biofuel consumption reduction seem necessary to improve North Korea's air quality.

Using ozonesonde measurements from 2015 to 2018 at the Jang Bogo station located in the southeastern Antarctic region, we evaluate ozone profiles retrieved from the three satellite measurements that are widely used: Ozone Monitoring Instrument (OMI), Microwave Limb Sounder (MLS), and Ozone Mapping Profiler Suite (OMPS) data. For the fair validation, ozonesonde profiles are smoothed using the weighting function of each satellite retrieval algorithm (i.e., convolution process). Compared with limb-viewing MLS and OMPS ozone profiles, the OMI ozone profiles are relatively less qualified: coarser vertical resolution and larger inter-annual variation. Nevertheless, our validation reveals that the quality of all three satellite ozone profiles looks comparable; In general, difference from ozonesonde profile is ∼1 ppm absolutely, and -20 to 30% relatively at maximum. This quantitative range well corresponds to previous work, meaning that our new validation confirms the reliability of satellite ozone profiles in the southeastern Antarctic region where the measurement data for the validation were not enough. Another interesting feature is the role of a priori ozone profile; Nadir-viewing OMI satellite can have qualified ozone profiles by a proper assumption of a priori ozone profile. Since the performance of limb-viewing ozone profiles is better, however, the careful usage of nadir-viewing ozone profile is still required. We think that the simultaneous usage of multiple satellite ozone profiles can contribute to better understanding of Antarctic ozone characteristics.

We use Aerosol Robotic Network (AERONET) observation data to empirically determine how natural and anthropogenic aerosol categories (i.e. mineral dust, biomass burning, and urban-industrial aerosols) affect light extinction, showing that their radiative forcing varies strongly with the surface albedo. Generally, the radiative forcing depends on the aerosol loading, but the efficiency varies with the aerosol type and aerosol-radiation-surface interactions. Desert dust, biomass burning and urban-industrial aerosols can exhibit dramatic shifts in radiative forcing at the top of the atmosphere, from cooling to warming, at surface albedos from below 0.5 to above 0.75. Based on the linear relationship between the radiative forcing efficiency and surface albedo for aeolian aerosols, using Moderate Resolution Imaging Spectroradiometer (MODIS) AOT (Aerosol Optical Thickness) and surface albedo data, we characterized a large Asian dust event during the spring of 2001, and demonstrate its immense spatially varying radiative forcing, ranging from about −84.0 to +69.3 W/m2. For extensive Russian wildfires during the summer of 2010, strong radiative cooling forcing variability of biomass combustion aerosols is found, ranging from about −86.3 to +3.1 W/m2. For a thick urban-industrial aerosol haze over northern India during the winter of 2017, a large range of about −85.0 to −0.3 W/m2 is found. These wide ranges underscore the need to accurately define aerosol-radiation-surface interactions.

In this present study, an aerosol effective height (AEH) retrieval algorithm has been developed using the O4 air mass factor (AMF) at 477 nm from the hyperspectral Ozone Monitoring Instrument (OMI). We investigated the magnitude of change in topographical and seasonal O4 vertical column density (VCD) in Northeast Asia and evaluated its effect on AEH retrieval accuracy using our AEH retrieval algorithm. In addition, the effect of a temperature-dependent cross-section for O4 (TDCS) on Look Up Table (LUT)-based AEH retrieval accuracy was quantified. A comparison between the retrieved AEH and those from the NIES lidar network for the period from January 2005 to June 2009, applying both the TDCS and the seasonal and topographical O4 VCDs, resulted in a root mean square error (RMSE) of 0.44 km for both smoke and dust aerosols. However, when both a TDCS (an O4 absorption cross-section at a single temperature of 293 K; SCS) and a single O4 VCD value were applied to the LUT, the RMSE for both aerosol types was calculated to be 0.52 km (0.51 km), which implies that TDCS contributes most to AEH retrieval accuracy when accurate O4 VCDs are applied to the LUT. For smoke aerosols only, both TDCS and multiple O4 VCD (SCS and single O4 VCD) applications had RMSE values of 0.46 km (0.66 km). The retrieved AEHs were additionally compared with satellite-based lidar measurements. We also investigated the effects of uncertainties in our algorithm input data (e.g., O4 VCD, TDCS, AOD, and surface reflectance) on AEH retrieval error using synthetic radiances. Large errors can be caused by uncertainties in O4 VCD and AOD. In particular (0.4 ≤ AOD

We investigated the influence of long-range transboundary transport (LRTT) on the aerosol concentrations in the Korean peninsula using the ground- and satellite-based remote sensing with back-trajectory calculations during the Korea-United States Air Quality (KORUS-AQ) campaign. Specifically, aerosol optical depth (AOD) observations from a geostationary satellite can directly provide the progression and evolution of aerosol plume transport. During high pollution cases in western Korea, we found the AOD enhancement over the Yellow Sea and east-central China, at maximum >200% over the pathway of LRTT compared to the mean condition. Particularly, high AOD in the Shandong peninsula appears coincidentally with the high AOD over South Korea in a day, revealing the strong influence of the east-central Chinese emission. Back-trajectory patterns remarkably capture the movement of high AOD bands detected by the geostationary satellite monitoring. LRTT cases through the inside of boundary layer at east-central China usually contribute to the high AOD in Korea, while air-masses above the boundary layer in north China and Mongolia do not much relate to the Korean pollution, showing the importance for both the direction and height of the air-mass movement. Travel speed is another significant factor to describe the LRTT effect. Despite the large effect of LRTT to both urban and rural sites in Korea, sometimes urban sites are more affected by the domestic emission when the air-mass travels shorter than ∼250 km per day, notifying that the effect of Korean domestic emission cannot be negligible as well. Our findings reveal that usage of geostationary satellite observations enables us to better evaluate the influence of LRTT on the local air pollution.

We investigated the characteristics of the total ozone column (TOC) around West Antarctica (near the Weddell Sea) compared with ambient meteorological factors. For this analysis, we used ground-based and satellite TOC measurements as well as meteorology (air temperature, potential vorticity and wind field) from reanalysis data. Long-term patterns of TOC show the large year-to-year variation (e.g., maximumly ∼200 DU at King Sejong) but a steady recovering trend recently. Despite a generally consistent pattern, the TOC around West Antarctica did not correlate well between high- and low-latitude regions during austral spring; this result implies that the ozone hole area had a spatial variation over West Antarctica. The TOC pattern around West Antarctica correlated well with air temperature but showed a vertical difference; high positive correlations appeared in the lower stratosphere (maximumly R > 0.9 at ∼50–100 hPa height) showing enhanced ozone depletion in colder conditions, but negative correlations appeared in the upper stratosphere (minimum R 0.9 at ∼500–600 K height) during the austral spring but a moderately negative correlation in the lower stratosphere (minimum R

In this study, Geostationary Ocean Color Imager (GOCI) AOD and Visible Infrared Imaging Radiometer Suite (VIIRS) AOD data were assimilated to forecast surface PM2.5 concentrations over Eastern China, by using the three–dimensional variational (3DAVR) data assimilation (DA) system, to compare DA impacts by assimilating AOD retrievals from these two types of satellites. Three experiments were conducted, including a CONTROL without the AOD assimilation, and GOCIDA and VIIRSDA with the assimilation of AOD retrievals from GOCI and VIIRS, respectively. By utilizing the Weather Research and Forecasting with Chemistry (WRF/Chem) model, 48-h forecasts were initialized at each 06 UTC from 19 November to 06 December 2013. These forecasts were evaluated with 248 ground-based measurements from the air quality monitoring network across 67 China cities. The results show that overall the CONTROL underestimated surface PM2.5 concentrations, especially over Jing–Jin–Ji (JJJ) region and Yangtze River Delta (YRD) region. Both the GOCIDA and VIIRSDA produced higher surface PM2.5 concentrations mainly over Eastern China, which fits well with the PM2.5 measurements at these eastern sites, with more than 8% error reductions (ER). Moreover, compared to CONTROL, GOCIDA reduced 14.0% and 6.4% error on JJJ region and YRD region, respectively, while VIIRSDA reduced respectively 2.0% and 13.4% error over the corresponding areas. During the heavy polluted period, VIIRSDA improved all sites within YRD region, and GOCIDA enhanced 84% sites. Meanwhile, GOCIDA improved 84% sites on JJJ region, while VIIRSDA did not affect that region. These geographic distinctions might result from spatial dissimilarity between GOCI AOD and VIIRS AOD at time intervals. Moreover, the larger increment produced by AOD DA under stable meteorological conditions could lead to a longer duration (e.g., 1–2 days, > 2 days) of AOD DA impacts. Even though with AOD DA, surface PM2.5 concentrations were still underestimated clearly over heavy polluted periods. And 3% sites performed worse, where low PM2.5 values were observed and CONTROL performed well. With this study, the results indicate that AOD DA can partially improve the accuracy of PM2.5 forecasts. And the obvious geographic differences on forecasts emphasize the potential and importance of combining AOD retrievals from GOCI and VIIRS into data assimilation.

Clouds are an important component of the atmosphere that affects both climate and weather, however, their contributions can be very difficult to determine. Ceilometer measurements can provide high resolution information on atmospheric conditions such as cloud base height (CBH) and vertical frequency of cloud occurrence (CVF). This study presents the first comprehensive analysis of CBH and CVF derived using Vaisala CL51 ceilometers at two urban stations in Seoul, Korea, during a three-year period from January 2014 to December 2016. The average frequency of cloud occurrence detected by the ceilometers is 54.3%. It is found that the CL51 is better able to capture CBH as compared to another ceilometer CL31 at a nearby meteorological station because it could detect high clouds more accurately. Frequency distributions for CBH up to 13,000 m providing detailed vertical features with 500-m interval show 55% of CBHs below 2 km for aggregated CBHs. A bimodal frequency distribution was observed for three-layers CBHs. A monthly variation of CVF reveals that frequency concentration of lower clouds is found in summer and winter, and higher clouds more often detected in spring and autumn. Monthly distribution features of cloud occurrence and precipitation are depending on seasons and it might be easy to define their relationship due to higher degree of variability of precipitation than cloud occurrence. However, a fluctuation of cloud occurrence frequency in summer is similar to precipitation in trend, whereas clouds in winter are relatively frequent but precipitation is not accompanied. In addition, recent decrease of summer precipitation could be mostly explained by a decrease of cloud occurrence. Anomalous precipitation recorded sometimes is considerably related to corresponding cloud occurrence. The diurnal and daily variations of CBH and CVF from ceilometer observations and the analysis of microwave radiometer measurements for two typical cloudiness cases are also reviewed in parallel. This analysis in finer temporal scale exhibits that utilization of ground-based observations together could help to analyze the cloud behaviors.

In this study, we present and compare regional correlations between CO total column density (TCD CO ) from the data set of Measurement of Pollution in the Troposphere (MOPITT), and high-absorbing BC dominant aerosol optical depth (AOD BC ) from the retrieval algorithm using Moderate Resolution Imaging Spectroradiometer (MODIS) and Ozone Monitoring Instrument (OMI) (MODIS-OMI algorithm, MOA). TCD CO shows positive relationship to both fine-mode AOD (AOD FM ) and AOD BC in general, but TCD CO better correlates with AOD BC than AOD FM . This enhanced correlation between TCD CO and AOD BC appears more clearly during spring and summer. Correlation between TCD CO and AOD BC is exceptionally poor in Northern Africa where the BC-dominated aerosols are frequently mixed with mineral dust particles from the Sahara. Another issue is also found in Southern Africa; the correlation between AOD BC and TCD CO in this region is not much higher than that between the AOD FM and TCD CO in spite of large occurrence of biomass burning and wildfire. This can be explained by the cloud perturbation near the source regions and dispersion effect due to the typical wind pattern. Correlations between AOD BC and TCD CO increase further when fire detected areas are only considered, but does not change much over the urban area. This difference clarifies the large contribution of burning events to the positive relationship between BC and CO. All findings in this study demonstrate a possible use of satellite CO product in evaluating the BC-dominated aerosol product from satellite remote sensing over the globe.

Aerosols affect the insolation at ground and thus the Aerosol Optical Depth (AOD, a measure of aerosol pollution) plays an important role on the variation of the Physiological Equivalent Temperature (PET) at locations with different aerosol climatology. The aerosol effects upon PET were studied for the first time at four East Asian cities by coupling a radiative transfer model and a human thermal comfort model which were previously well evaluated. Evident with the MODIS and AERONET AOD observations, the aerosol pollution at Beijing and Seoul was higher than at Chiayi (Taiwan) and Hong Kong. Based on the AERONET data, with background AOD levels the selected temperate cities had similar clear-sky PET values especially during summertime, due to their locations at similar latitudes. This also applied to the sub-tropical cities. Increase in the AOD level to the seasonal average one led to an increase in diffuse solar radiation and in turn an increase in PET for people living in all the cities. However, the heavy aerosol loading environment in Beijing and Seoul in summertime (AODs > 3.0 in episodic situations) reduced the total radiative flux and thus PET values in the cities. On the contrary, relatively lower episodic AOD levels in Chiayi and Hong Kong led to strong diffuse and still strong direct radiative fluxes and resulted in higher PET values, relative to those with seasonal averaged AOD levels. People tended to feel from “hot” to “very hot” during summertime when the AOD reached their average levels from the background level. This implies that in future aerosol effects add further burden to the thermal environment apart from the effects of greenhouse gas-induced global warming. Understanding the interaction between ambient aerosols and outdoor thermal environment is an important first step for effective mitigation measures such as urban greening to reduce the risk of human heat stress. It is also critical to make cities more attractive and enhancing to human well-being to achieve enhancing sustainable urbanization as one of the principal goals for the Nature-based Solutions.

Korea will launch the Geostationary Environment Monitoring Spectrometer (GEMS) instrument in 2018 onboard the Geostationary Korean Multi-Purpose Satellite to monitor tropospheric gas concentrations with high temporal and spatial resolutions. The purpose of this study is to examine the performance of total column ozone (TCO) measurements from ground-based Pandora and Brewer instruments that will be used for validation of the GEMS ozone product. Satellite measurements can be used to detect erroneous outliers at a particular ground station, which deviate significantly from co-located satellite measurements relative to other stations. This is possible because a single satellite retrieval algorithm is used to process the entire satellite dataset, and instrument characteristics typically change slowly over the life of the satellite. Thus, the short-term stability (months) of satellite measurements can be used to estimate the performance of the ground-based measurement network as well as to identify potential problems at individual stations. As a reference for satellite ozone measurements, we have selected TCO data derived from OMI-TOMS V8.5 algorithm, because it is a robust algorithm that has been well studied to identify its various error sources. We validated ground-based Brewer and Pandora TCO measurements using OMI-TOMS TCO data collected over South Korea from March 2012 to December 2014. The Brewer TCO measurements at Pohang showed significant deviation from overall seasonal variation during the study period. In addition, in the presence of clouds, Pandora TCO measurements are unusually ∼7% higher than OMI-TOMS TCO data. To filter out these cloud-contaminated data, we applied a Kalman filter to the Pandora measurements. The diurnal variation in the Kalman-filtered Pandora data agrees well with the Brewer data, and the correlation of Kalman-filtered Pandora data with OMI-TOMS TCO is significantly improved from 0.89 to 0.99 at Seoul and from 0.93 to 0.99 at Busan.

The sensitivities of oxygen dimer (O4) slant column densities (SCDs) were examined by applying temperature-dependent O4 cross sections using the radiative transfer model (RTM) calculation with the linearized pseudo-spherical vector discrete ordinate radiative transfer model. For the sensitivity study, we used a newly developed cross section database in place of the database used in the operational algorithm. Newly investigated O4 cross section databases for 203 K and 293 K were used for the radiance simulation by interpolating temperature for each atmospheric layer based on the vertical profile of standard atmosphere in the RTM. The effect of the temperature-dependent cross sections was a significant O4 SCD increase of 8.3% with dependence on satellite and solar viewing geometries. Furthermore, the O4 SCD generally increased by an estimated 3.9% based on the observation geometries of the Ozone Monitoring Instrument. For the long-term comparison, the O4 SCD estimated from the temperature-dependent cross sections corrects 20% of the total underestimation of O4 SCD between the observation and simulation. Although the surface pressure variation and background aerosol effect also correct the O4 SCD discrepancy, the effect of temperature-dependent cross sections was more important than the effects of surface pressure variation and background aerosols. Therefore, temperature dependence of the cross section in the RTM calculation is essential for the accurate simulation of O4 SCD.

It is important to estimate the effects of the long-range transport of atmospheric pollutants for efficient and effective strategies to control air quality. In this study, the contributions of trans-boundary transport to the mean concentrations of SO 2 , NO 2 , CO, and PM 10 in Seoul, Korea from 2001 to 2014 were estimated based on the conditional potential source contribution function (CPSCF) method. Eastern China was found to be the major source of trans-boundary pollution in Seoul, but moderate sources were also located in northeastern China. The contribution of long-range transport from Japan was negligible. The spatial distributions of the potential source contribution function (PSCF) values of each pollutant showed reasonable consistency with their emission inventory and satellite products. The PSCF values of SO 2 and PM 10 from eastern China were higher than those of NO 2 and CO. The mean concentrations of SO 2 , NO 2 , CO, and PM 10 in Seoul for the period from 2001 to 2014 were 5.34, 37.0, and 619.1 ppb, and 57.4 4 μg/m 3 , respectively. The contributions of long-range transport to the mean concentrations of SO 2 , NO 2 , CO, and PM 10 in Seoul were 0.74, 3.4, and 39.0 ppb, and 12.1 μg/m 3 , respectively, which are 14%, 9%, 6%, and 21% of the mean concentrations, respectively. The annual mean concentrations of SO 2 and NO 2 followed statistically significant increasing linear trends (0.5 and 1.6 ppb per decade, respectively), whereas the trends in the annual mean concentrations of CO and PM 10 were statistically insignificant. The trends in the ratio of the increased concentrations associated with long-range transport to the annual mean concentrations of the pollutants were statistically insignificant. However, the results indicate that the trans-boundary transport of SO 2 , NO 2 , CO, and PM 10 from eastern China consistently affected air quality in Seoul over the study period (2001–2014). Regionally, the effects of the long-range transport of pollutants from Beijing and Harbin-Changchun on air quality in Seoul have become more significant over this period.

PM2.5 has been considered as a crucial issue in densely populated cities because of its adverse effects on human health. As a way to mitigate this problem on city scale, urban forest is recently suggested as a solution due to its potential to absorb and adhere PM2.5. However, limited observations in the forest prevent a full understanding in the role of forest on urban PM2.5 concentration. In this paper, we present an application of deep learning using satellite data to clarify the role of forest with respect to the PM2.5 concentration mitigation in the city. Based on PM2.5 data collected from the ground-based observation stations, two PM2.5 prediction models are constructed through the deep learning approach. Satellite-derived aerosol optical depth from the GOCI and MODIS are used as the main predictors of two models. Both models predict spatial distribution throughout Seoul, Korea (R2 of 0.61 and 0.78). Particularly, the western parts of Seoul tend to have higher PM2.5 concentrations than the other parts, whereas mid-outskirts have noticeably low concentrations. A comparison of spatial distributions of PM2.5 between observations and predictions show that the existing observation network only reflects 15%–60% of entire characteristics of Seoul. Utilizing city-wide PM2.5 estimations, a comparison of estimated PM2.5 between urban and forest regions has been performed. The results show that the estimated PM2.5 concentrations in the forest regions are less than those in urban regions by up to 16.4 μg m−3. In contrast to urban regions, the average of PM2.5 concentrations in the forest regions is likely below the daily mean WHO PM2.5 outdoor standard. Our study suggests that urban forest could be a potential way to improve urban air quality with a specific focus on PM2.5. In addition, the deep learning approach used in this study can be applied to other cities where obtaining observation measurements is difficult.

In this study, we examined the change rates of PM2.5 concentrations, aerosol optical depth (AOD), and the concentrations of PM2.5 precursors, such as SO2 and NO2, in China and South Korea using surface and satellite observations from 2015 to 2018. To quantify the impacts of the emissions and meteorology on the concentration changes, we performed a series of air quality simulations with year-specific meteorology and a fixed anthropogenic emissions inventory. The surface PM2.5 observations in China and South Korea decreased at rates of 9.1 and 4.3%/yr during the study period, respectively. The AODs from Moderate Resolution Imaging Spectroradiometer (MODIS) and Geostationary Ocean Color Imager (GOCI) also decreased faster over China than the AODs over South Korea. For the PM2.5 decrease in China, the emission impact was more significant (73%) than the meteorology impact (27%). On the contrary, in South Korea, the emissions and meteorology impacts on PM2.5 reductions were similar (51% vs 49%). The SO2 concentration over China in 2018 significantly reduced to approximately half of the level in 2015. In turn, the sulfate concentration in Baengnyeong (BN), located in a downwind pathway from China to South Korea, decreased at a rate of 0.79%/month. However, the nitrate concentration in BN showed an increasing trend due to the non-linear chemical reactions among sulfate-nitrate-ammonium. The increased nitrate compensated for the reduced PM2.5 concentration from the sulfate decrease at BN. Additionally, the number of high (>50 μg/m3) PM2.5 concentration days continuously decreased in China, but the number in South Korea increased. It is noted that emission reductions in an upwind area do not guarantee corresponding air quality improvement in the downwind area when complex secondary aerosol formation processes, as well as spatiotemporal changes in meteorology, are involved in the transboundary transport of air pollutants.

To better understand air quality issues in South Korea, it is essential to identify the main contributors of air pollution and to quantify the effects of transboundary transport. In this study, geostationary satellite measurements were used to assess the effects of aerosol transport on air quality in South Korea. This study proposes a method to define the long-range transport (LRT) of aerosols into the Korean Peninsula using remote sensing obervations and back-trajectories and estimates the LRT effects on air quality in Seoul using in-situ particulate matter (PM) measurements. Aerosol optical depths (AODs) are obtained from the Geostationary Ocean Color Imager (GOCI), and the back-trajectories are from the National Ocean and Atmospheric Administration (NOAA) HYbrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. For LRT events, satellite observations showed high AOD plumes over the Yellow Sea, a pathway between Eastern China and South Korea, and the movements of aerosol plumes transported to South Korea were also detected. PM2.5 concentrations, PM10 concentrations, and AOD during LRT increased by 52%, 49%, and 81%, respectively, relative to their average values for 2015–2018. To quantitatively characterize the LRT of aerosols, the effects of LRT on PM2.5 concentrations were estimated for each PM concentration category. The contribution of LRT to PM2.5 concentrations was estimated to be 33% during 2015–2018. When high concentrations of PM2.5 were observed in Seoul, they were likely to be associated with LRT events.

Springtime trans-Pacific transport of Asian air pollutants has been investigated in many ways to figure out its mechanism. Based on the Western Pacific (WP) pattern, one of climate variabilities in the Northern Hemisphere known to be associated with the pattern of atmospheric circulation over the North Pacific Ocean, in this study, we characterize the pattern of springtime trans-Pacific transport using long-term satellite measurements and reanalysis datasets. A positive WP pattern is characterized by intensification of the dipole structure between the northern Aleutian Low and the southern Pacific High over the North Pacific. The TOMS/OMI Aerosol Index (AI) and MOPITT CO show the enhancement of Asian pollutant transport across the Pacific during periods of positive WP pattern, particularly between 40 and 50°N. This enhancement is confirmed by high correlations of WP index with AI and CO between 40 and 50°N. To evaluate the influence of the WP pattern, we examine several cases of trans-Pacific transport reported in previous research. Interestingly, most trans-Pacific transport cases are associated with the positive WP pattern. During the period of negative WP pattern, reinforced cyclonic wave breaking is consistently found over the western North Pacific, which obstructs zonal advection across the North Pacific. However, some cases show the trans-Pacific transport of CO in the period of negative WP pattern, implying that the WP pattern is more influential on the transport of particles mostly emitted near ∼40°N. This study reveals that the WP pattern can be utilized to diagnose the strength of air pollutant transport from East Asia to North America.

Absorption and scattering characteristics of various aerosol events are investigated using 2-years of measurements from a skyradiometer at Yonsei University in Seoul, Korea. Both transported dust and anthropogenic aerosols are observed at distinct geo-location of Seoul, a megacity located a few thousand kilometers away from dust source regions in China. We focus on the wavelength dependence of Angstrom exponent (AE) and single scattering albedo (SSA), showing the characteristics of regional aerosols. The correlation between spectral SSAs and AEs calculated using different wavelength pairs generally indicates relatively weak absorption of fine-mode aerosols (urban pollution and/or biomass burning) and strong absorption of coarse-mode aerosols (desert dust) at this location. AE ratio (AER), a ratio of AEs calculated using wavelength pair between shorter (340–675 nm) and longer wavelength pair (675–1020 nm) correlates differently with SSA according to the dominant size of local aerosols. Correlations between SSA and AER show strong absorption of aerosols for AER 2.0. Based on the seasonal pattern of wavelength dependence of AER and SSA, this correlation difference looks to reveal the separated characteristics of transported dust and anthropogenic particles from urban pollution respectively. The seasonal characteristics of AER and SSAs also show that the skyradiometer measurement with multiple wavelengths may be able to detect the water soluble brown carbon, one of the important secondary organic aerosols in the summertime atmospheric composition.

Surface-level PM10 distribution was estimated from the satellite aerosol optical depth (AOD) products, taking the account of vertical profiles and hygroscopicity of aerosols over Jeju, Korea during March 2008 and October 2009. In this study, MODIS AOD data from the Terra and Aqua satellites were corrected with aerosol extinction profiles and relative humidity data. PBLH (Planetary Boundary Layer Height) was determined from MPLNET lidar-derived aerosol extinction coefficient profiles. Through statistical analysis, better agreement in correlation (R = 0.82) between the hourly PM10 concentration and hourly average Sunphotometer AOD was the obtained when vertical fraction method (VFM) considering Haze Layer Height (HLH) and hygroscopic growth factor f(RH) was used. The validity of the derived relationship between satellite AOD and surface PM10 concentration clearly demonstrates that satellite AOD data can be utilized for remote sensing of spatial distribution of regional PM10 concentration.

Quantifying the spectral variation of column aerosol absorption in the ultraviolet (UV) and visible (Vis) wavelengths is required for accurate satellite-based aerosol and trace-gas retrievals. Retrievals of the column-averaged imaginary part of refractive index and single scattering albedo (SSA) in the UV–Vis range have been performed at Yonsei University, Seoul, Korea, since 2016 by combining co-located measurements from the NASA Aerosol Robotic Network (AERONET) Cimel sun-sky photometer, the Ultraviolet Multifilter Rotating Shadowband Radiometer (UV-MFRSR), the SKYNET Prede sky radiometer, and the NASA Pandora sun spectrometer. We investigated the spectral variation of column-averaged imaginary part of refractive index for UV–Vis wavelengths to refine models used in our aerosol retrieval algorithm to process measurements from the upcoming Geostationary Environment Monitoring Satellite (GEMS). The retrieved imaginary part of refractive index for highly absorbing fine pollution particles (BC), dust (DS), and non-absorbing (NA) particles in the selected UV–Vis range (380–440 nm) showed 0–20%, 30%, and 0–40% of spectral dependence, respectively. Retrievals of Ozone Monitoring Instrument (OMI) measurement data using the improved aerosol model showed improved correlation with AERONET data compared to the old algorithm that did not properly account for aerosol absorption effects. These results corroborate the advantage of using local climatology derived from ground-based UV–Vis spectral aerosol absorption measurements for satellite GEMS aerosol retrievals over East Asia. Moreover, this study reveals that spectral variations in the UV column aerosol absorption in East Asia differ from those in other regions.

This investigation examines aerosol dynamics during major fine mode aerosol transboundary pollution events in South Korea primarily during the KORUS-AQ campaign from May 1 – June 10, 2016, particularly when cloud fraction was high and/or fog was present to quantify the change in aerosol characteristics due to near-cloud or fog interaction. We analyze the new AERONET Version 3 data that have significant changes to cloud screening algorithms, allowing many more fine-mode observations in the near vicinity of clouds or fog. Case studies for detailed investigation include May 25–26, 2016 when cloud fraction was high over much of the peninsula, associated with a weak frontal passage and advection of pollution from China. These cloud-influenced Chinese transport dates also had the highest aerosol optical depth (AOD), surface PM2.5 concentrations and fine mode particle sizes of the entire campaign. Another likewise cloud/high relative humidity (RH) case is June 9 and 10, 2016 when fog was present over the Yellow Sea that appears to have affected aerosol properties well downwind over the Korean peninsula. In comparison we also investigated aerosol properties on air stagnation days with very low cloud cover and relatively low RH (May 17 & 18, 2016), when local Korean emissions dominated. Aerosol volume size distributions show marked differences between the transport days (with high RH and cloud influences) and the local pollution stagnation days, with total column-integrated particle fine mode volume being an order of magnitude greater on the pollution transport dates. The PM2.5 over central Seoul were significantly greater than for coastal sites on the transboundary transport days yet not on stagnation days, suggesting additional particle formation from gaseous urban emissions in cloud/fog droplets and/or in the high RH humidified aerosol environment. Many days had KORUS-AQ research aircraft flights that provided observations of aerosol absorption, particle chemistry and vertical profiles of extinction. AERONET retrievals and aircraft in situ measurements both showed high single scattering albedo (weak absorption) on the cloudy or cloud influenced days, plus aircraft profile in situ measurements showed large AOD enhancements (versus dried aerosol) at ambient relative humidity (RH) on the pollution transport days, consistent with the significantly larger fine mode particle radii and weak absorption.

The Geostationary Trace gas and Aerosol Sensor Optimization (GeoTASO) instrument is an airborne hyperspectral spectrometer measuring backscattered solar radiation in the ultraviolet (290–400 nm) and visible (415–695 nm) wavelength regions. This paper presents high-resolution sulfur dioxide (SO2) maps over the Korean Peninsula, produced by SO2 retrievals from GeoTASO measurements during the Korea–United States Air Quality Field Study (KORUS-AQ) from May to June 2016. The highly sensitive GeoTASO instrument with a spatial resolution of ~250 m × 250 m can detect point emission sources of SO2 within its fields of view, even without merging multiple overlapping observations. To retrieve SO2 vertical columns from the GeoTASO measurements, we apply an algorithm based on principal component analysis (PCA), which is effective in suppressing noise and biases in SO2 retrievals. The retrievals successfully capture SO2 plumes and various point sources such as power plants, a petrochemical complex, and a steel mill, located in South Chungcheong Province, some of which are not detected by a ground-based in situ measurement network. Spatial distributions of SO2 from GeoTASO observations in source areas are consistent with those from the Stack Tele-Monitoring System reports and airborne in situ SO2 measurements. Comparisons of SO2 retrievals from GeoTASO and existing satellite sensors demonstrate the significance of high-resolution SO2 observations, by indicating that GeoTASO detects small SO2 emission sources that are not precisely resolved by single overpasses of satellites. To assess future geostationary SO2 observations having a higher spatial resolution, we upscale the GeoTASO SO2 retrievals to a spatial resolution of the Geostationary Environment Monitoring Spectrometer (GEMS). Since the upscaled GeoTASO retrievals also detect SO2 plumes clearly, we expect from GEMS to identify even small SO2 emission sources over Asia.

In the developing countries such as China, most well-developed areas have suffered severe haze pollution, which was associated with increased premature morbidity and mortality and attracted widespread public concerns. Since ground-based PM2.5 monitoring has limited temporal and spatial coverage, satellite aerosol remote sensing data has been increasingly applied to map large-scale PM2.5 characteristics through advanced spatial statistical models. Although most existing research has taken advantage of the polar orbiting satellite instruments, a major limitation of the polar orbiting platform is its limited sampling frequency (e.g., 1-2 times/day), which is insufficient for capturing the PM2.5 variability during short but intense heavy haze episodes. As the first attempt, we quantitatively investigated the feasibility of using the aerosol optical depth (AOD) data retrieved by the Geostationary Ocean Color Imager (GOCI) to estimate hourly PM2.5 concentrations during winter haze episodes in the Yangtze River Delta (YRD). We developed a three-stage spatial statistical model, using GOCI AOD and fine mode fraction, as well as corresponding monitoring PM2.5 concentrations, meteorological and land use data on a 6-km modeling grid with complete coverage in time and space. The 10-fold cross-validation R2 was 0.72 with a regression slope of 1.01 between observed and predicted hourly PM2.5 concentrations. After gap filling, the R2 value for the three-stage model was 0.68. We further analyzed two representative large regional episodes, i.e., a "multi-process diffusion episode" during December 21-26, 2015 and a "Chinese New Year episode" during February 7-8, 2016. We concluded that AOD retrieved by geostationary satellites could serve as a new valuable data source for analyzing the heavy air pollution episodes.

This study investigated how cloud fraction and snow cover affect the variation of surface ultraviolet (UV) radiation by using surface Erythemal UV (EUV) and Near UV (NUV) observed at the King Sejong Station, Antarctica. First the Radiative Amplification Factor (RAF), the relative change of surface EUV according to the total-column ozone amount, is compared for different cloud fractions and solar zenith angles (SZAs). Generally, all cloudy conditions show that the increase of RAF as SZA becomes larger, showing the larger effects of vertical columnar ozone. For given SZA cases, the EUV transmission through mean cloud layer gradually decreases as cloud fraction increases, but sometimes the maximum of surface EUV appears under partly cloudy conditions. The high surface EUV transmittance under broken cloud conditions seems due to the re-radiation of scattered EUV by cloud particles. NUV transmission through mean cloud layer also decreases as cloud amount increases but the sensitivity to the cloud fraction is larger than EUV. Both EUV and NUV radiations at the surface are also enhanced by the snow cover, and their enhancement becomes higher as SZA increases implying the diurnal variation of surface albedo. This effect of snow cover seems large under the overcast sky because of the stronger interaction between snow surface and cloudy sky.

This study examined the quiescence of Asian dust events in South Korea and Japan during the spring of 2012, presenting a synoptic characterization and suggesting possible causes. Synoptic observation reports from the two countries confirmed that spring 2012 had the lowest number of dust events in 2000–2012. The monthly dust frequency (DF) in March 2012 over the dust source regions, i.e., deserts in northern China and Mongolia, indicated a significant decrease compared to the 12 year (2000–2011) March climatology. The DF in April 2012 was comparable to the 12 year climatology values, but in May 2012 it was slightly lower. The daily Ozone Monitoring Instrument Aerosol Index and the Navy Aerosol Analysis and Prediction System simulations revealed stagnant dust movement in March and May 2012. Anomalous anticyclones north of the source regions decreased the dust outbreaks and enhanced the southeasterly winds, resulting in few dust events over the downwind countries (i.e., South Korea and Japan). By contrast, in April 2012, a strong anomalous cyclone east of Lake Baikal slightly increased the dust outbreaks over northeastern China. However, the major dust outbreaks were not transported downwind because of exceptional dust pathways, i.e., the southeastward pathway of dust transport was unusually blocked by the expansion of an anomalous anticyclonic circulation over the Sea of Okhotsk, with dust being transported northeast.

Dust storms are known to have adverse effects on human health and significant impact on weather, air quality, hydrological cycle, and ecosystem. Atmospheric dust loading is also one of the large uncertainties in global climate modeling, due to its significant impact on the radiation budget and atmospheric stability. Observations of dust storms in humid tropical south China (e.g. Hong Kong), are challenging due to high industrial pollution from the nearby Pearl River Delta region. This study develops a method for dust storm detection by combining ground station observations (PM10 concentration, AERONET data), geostationary satellite images (MTSAT), and numerical weather and climatic forecasting products (WRF/Chem). The method is based on a hybrid neural network (NN) retrieval model for two scales: (i) a NN model for near real-time detection of dust storms at broader regional scale; (ii) a NN model for detailed dust storm mapping for Hong Kong and Taiwan. A feed-forward multilayer perceptron (MLP) NN, trained using back propagation (BP) algorithm, was developed and validated by the k-fold cross validation approach. The accuracy of the near real-time detection MLP-BP network is 96.6%, and the accuracies for the detailed MLP-BP neural network for Hong Kong and Taiwan is 74.8%. This newly automated multi-scale hybrid method can be used to give advance near real-time mapping of dust storms for environmental authorities and the public. It is also beneficial for identifying spatial locations of adverse air quality conditions, and estimates of low visibility associated with dust events for port and airport authorities.

A unified satellite algorithm is presented to simultaneously retrieve aerosol properties (aerosol optical depth; AOD and aerosol type) and clear-sky shortwave direct radiative effect (hereafter, DREA) over ocean. The algorithm is applied to Moderate Resolution Imaging spectroradiometer (MODIS) observations for a period from 2003 to 2010 to assess the DREA over the global ocean. The simultaneous retrieval utilizes lookup table (LUT) containing both spectral reflectances and solar irradiances calculated using a single radiative transfer model with the same aerosol input data. This study finds that aerosols cool the top-of-atmosphere (TOA) and bottom-of-atmosphere (BOA) by 5.2 +/- 0.5 W/sq m and 8.3 W/sq m, respectively, and correspondingly warm the atmosphere (hereafter, ATM) by 3.1 W/sq m. These quantities, solely based on the MODIS observations, are consistent with those of previous studies incorporating chemical transport model simulations and satellite observations. However, the DREAs at BOA and ATM are expected to be less accurate compared to that of TOA due to low sensitivity in retrieving aerosol type information, which is related with the atmospheric heating by aerosols, particularly in low AOD conditions; consequently, the uncertainties could not be quantified. Despite the issue in the aerosol type information, the present method allows us to confine the DREA attributed only to fine-mode dominant aerosols, which are expected to be mostly anthropogenic origin, in the range from 1.1 W/sq m to 1.3 W/sq m at TOA. Improvements in size-resolved AOD and SSA retrievals from current and upcoming satellite instruments are suggested to better assess the DREA, particularly at BOA and ATM, where aerosol absorptivity induces substantial uncertainty.

Despite continuous efforts to retrieve aerosol optical depth (AOD) using a conventional 5-channelmeteorological imager in geostationary orbit, the accuracy in urban areas has been poorer than other areas primarily due to complex urban surface properties and mixed aerosol types from different emission sources. The two largest error sources in aerosol retrieval have been aerosol type selection and surface reflectance. In selecting the aerosol type from a single visible channel, the season-dependent aerosol optical properties were adopted from longterm measurements of Aerosol Robotic Network (AERONET) sun-photometers. With the aerosol optical properties obtained fromthe AERONET inversion data, look-up tableswere calculated by using a radiative transfer code: the Second Simulation of the Satellite Signal in the Solar Spectrum (6S). Surface reflectance was estimated using the clear sky composite method, awidely used technique for geostationary retrievals. Over East Asia, the AOD retrieved from the Meteorological Imager showed good agreement, although the values were affected by cloud contamination errors. However, the conventional retrieval of the AOD over Hong Kong was largely underestimated due to the lack of information on the aerosol type and surface properties. To detect spatial and temporal variation of aerosol type over the area, the critical reflectance method, a technique to retrieve single scattering albedo (SSA), was applied. Additionally, the background aerosol effect was corrected to improve the accuracy of the surface reflectance over Hong Kong. The AOD retrieved froma modified algorithmwas compared to the collocated data measured by AERONET in Hong Kong. The comparison showed that the new aerosol type selection using the critical reflectance and the corrected surface reflectance significantly improved the accuracy of AODs in Hong Kong areas,with a correlation coefficient increase from0.65 to 0.76 and a regression line change from τMI [basic algorithm] = 0.41τAERONET + 0.16 to τMI [new algorithm] = 0.70τAERONET + 0.01.

A new dust detection algorithm is developed by combining the results of multiple dust detection methods using IR channels onboard the MODerate resolution Imaging Spectroradiometer (MODIS). Brightness Temperature Difference (BTD) between two wavelength channels has been used widely in previous dust detection methods. However, BTD methods have limitations in identifying the offset values of the BTD to discriminate clear-sky areas. The current algorithm overcomes the disadvantages of previous dust detection methods by considering the Brightness Temperature Ratio (BTR) values of the dual wavelength channels with 30-day composite, the optical properties of the dust particles, the variability of surface properties, and the cloud contamination. Therefore, the current algorithm shows improvements in detecting the dust loaded region over land during daytime. Finally, the confidence index of the current dust algorithm is shown in 10 × 10 pixels of the MODIS observations. From January to June, 2006, the results of the current algorithm are within 64 to 81% of those found using the fine mode fraction (FMF) and aerosol index (AI) from the MODIS and Ozone Monitoring Instrument (OMI). The agreement between the results of the current algorithm and the OMI AI over the non-polluted land also ranges from 60 to 67% to avoid errors due to the anthropogenic aerosol. In addition, the developed algorithm shows statistically significant results at four AErosol RObotic NETwork (AERONET) sites in East Asia.

In this paper, we introduce a new method to estimate the change in mean mixing ratio of a target species at a receptor site due to the contribution of the long-range transport (CLRT). We applied our method to determine inter-annual and inter-seasonal variations in the CLRT of SO2 in Seoul, a major megacity in northeast Asia, during the period from 2001 to 2010. The major potential source areas of SO2 for the 2001–2010 period were located in East China according to the potential source contribution function (PSCF) maps. The CLRT of SO2 in Seoul was estimated to range from 0.40 to 1.03 ppb, which accounted for 8–21% of the ambient mean SO2 mixing ratio in Seoul. The inter-annual variations of estimated CLRT of SO2 was well correlated with those of the total emissions in China during the period of 2001–2008 (R = 0.85). We found that both local emissions from around Seoul and long-range transport from East China, especially the Shandong peninsula, affected the SO2 mixing ratio in Seoul throughout the decade of study. The CLRT of SO2 in Seoul increased after 2007 even though the total emissions of SO2 by China have been decreasing since 2006. The CLRT of SO2 in Seoul was high in spring and winter, which can be attributed to enhanced SO2 emissions in East China during these seasons and a dominant westerly wind. The CLRTs of SO2 accounted for 15, 11, 4, and 12% of the seasonal mean SO2 mixing ratio in spring, summer, fall, and winter, respectively. The uncertainty ranged from 24 to 62% of the estimated CLRT values.

In order to investigate seasonal and diurnal variation of primary organic carbon (POC) and secondary organic carbon (SOC) concentrations in a megacity, hourly measurements of particulate and gaseous pollutants were carried out in Seoul from January to December 2010. The EC Tracer Method (ECTM) and the Multiple Regression Method (MRM) have been used to estimate seasonal and diurnal concentrations of POC and SOC concentrations. Annual mean SOC concentrations estimated by ECTM (SOCECTM) and MRM (SOCMRM) accounted for 14.61 and 17.21% of TOC concentrations, respectively. Seasonal patterns in SOCMRM were comparable to those of SOCECTM, but the annual average SOCMRM was about 15% greater than that of SOCECTM. In spring, however, a large discrepancy was observed between SOCECTM and SOCMRM, which is thought to be due to a high ozone concentration and primary TOC/EC ratio. Regarding the annual mean diurnal characteristics, POC concentration showed peaks around 10:00 and 00:00 local time that were also observed in diurnal variations of TOC and EC concentrations. Annual mean SOC concentration, however, showed peaks at around 15:00. In the morning over all seasons, we found discrepancies between SOCECTM and SOCMRM due to overestimated SOCECTM concentration. The diurnal variations in SOC concentrations were found to have seasonal characteristics. The diurnal pattern of SOC concentration in spring was similar to that in autumn, and SOC concentrations in all seasons with the exception of winter showed a peak at around 15:00. In summer, however, the SOC concentration peak at around 15:00 was greater by 70%, 81%, and 54% than the peaks seen in spring, autumn, and winter, respectively, which could be explained by the high ozone concentration and strong UV radiation in summer. From 10:00 to 15:00 in summer, the average increase rates in SOCECTM and SOCMRM were 0.39 and 0.24 μg m−3 h−1, respectively. In winter, negligible diurnal variations of estimated SOC concentrations demonstrate that SOC formation is less active than in other seasons. The high concentration level of mean SOC in winter could be attributed to a low mixing height or stagnant atmospheric condition.

Total column ozone (TCO) amounts observed by the Dobson spectrophotometer from 1985 to 2008 in Seoul and vertical ozone profiles obtained with the ozonesonde from 1995 to 2007 in Pohang were used to investigate the relationship between the occurrence of Secondary Ozone Peak (SOP) in the Upper Troposphere/Lower Stratosphere (UT/LS) layer and the enhancement in TCO over the Korean Peninsula. Based on Hybrid Single-Particle, Lagrangian Integrated Trajectory (HYSPLIT) simulations, the advection of a northern mid-latitudinal ozone-rich airmass from the northwest is closely related to SOP occurrences, which consequently lead to enhancements in the amount of ozone in both the UT/LS and the total column at stations in Korea. In addition, both the frequency of the northwesterly advection and the northern mid-latitudinal ozone amount are revealed to affect the amount of ozone in the UT/LS and total column by up to 7 DU. The relationship between the SOP occurrence frequency and the long-term TCO trend was investigated with observed data collected in all seasons. The UT/LS ozone enhancements, which are largely affected by SOP occurrences, are considered to be positively related to the TCO trend from 1985 to 2008 over the Korean Peninsula.

A measurement method combining multi-axis differential optical absorption spectroscopy (MAX-DOAS) and a transmissometer (TX) is introduced as a means of retrieving surface trace gas mixing ratios in ambient air. The combined measurement method was utilized to derive surface NO2 mixing ratios from 27 March to 11 May 2007 in Seoul, Korea. To convert the differential slant column density (DSCD) to the volume mixing ratio (VMR), the light path length (LPL) along the MAX-DOAS line of sight was derived using the light extinction coefficient and Angstrom exponent data obtained by a TX and sunphotometer, respectively. Temporal variations of the NO2 VMRs at the 0–1 km layer obtained from radiative transfer model (RTM) simulations coupled with MAX-DOAS data show similar patterns, but with reduced magnitudes, to the ground level data and those of the combined MAX-DOAS and TX measurements at 0.08 km. The NO2 VMRs retrieved by the combined measurement were in agreement with those obtained from the RTM simulations coupled with MAX-DOAS data and the in-situ measurements within 40 and 50%, respectively. The coefficient of determination (R2) of 0.75 was obtained between the combined measurement data sets and those of the RTM simulations coupled with MAX-DOAS data whereas that between the combined measurement data sets and those of the in-situ measurements was 0.53. The coefficient of determination (R2) between the data sets derived from the RTM simulations coupled with MAX-DOAS data and those of the in-situ measurements was 0.67 with the scatter of the correlation within the 50% range.

In this study, Community Multi-scale Air Quality (CMAQ) model simulations, using the INTEX-B (Intercontinental Chemical Transport Experiment-Phase B) emission inventory for North Korea and China, CAPSS (Clean Air Policy Support System) emission inventory for South Korea, and REAS (Regional Emission Inventory in Asia) emission inventory for Japan, were carried out over four seasonal episodes from 2006, with a fine grid resolution of 30 km × 30 km, in order to evaluate the accuracy of the NOx emissions over the Korean peninsula. The tropospheric NO2 columns from the CMAQ model simulations were then compared with those retrieved from a satellite sensor, Ozone Monitoring Instrument (OMI), over the Korean peninsula as well as briefly over East Asia. The results showed that the CMAQ modeling, using the NOx emissions from the CAPSS inventory over South Korea, produced tropospheric NO2 columns that were over-predicted by factors between 1.38 and 1.87 compared to the OMI-retrieved tropospheric NO2 columns. This appears to be in line with the findings from a previous study, i.e. when the ACE-ASIA emission inventory was used for the episodes from 2001 to 2003, the CMAQ modeling tended to produce NO2 columns that were ∼1.46 times larger than the GOME-derived NO2 columns over South Korea. On the other hand, over North Korea, the NOx emissions of the INTEX-B emission inventory appear to be overestimated by factors between 1.55 and 7.46 (3.18 over the four seasonal episodes), based on the comparison study between the CMAQ-simulated and OMI-retrieved tropospheric NO2 columns. This may be caused by the large uncertainty in the NOx emission fluxes from North Korea due to insufficient information on the economic activity and energy consumption related to the political instability in North Korea.

The northeast Asian dust process during the spring seasons in the years 1982–2006 was simulated by the Integrated Wind Erosion Modeling System (IWEMS). The influence of Arctic Oscillation (AO) on dust activities was investigated by analyzing surface observations and model simulations. There is a significant relationship between AO and dust activity; a positive AO phase is associated with decreased (increased) dust storm frequency in Mongolia (Taklimakan Desert) and enhanced anticyclonic (southeastward) dust transport over northwestern China (North China). The AO-dust relation is mainly due to changes in the westerly jet and geopotential height in the middle troposphere; a positive AO phase induces a northward shift of the polar jet, an intensified westerly jet over northern Tibetan Plateau, and a positive geopotential height anomaly over Mongolia. The northern shift of the polar jet reduces the frequency of intense cyclones in Mongolia, thereby causing a decrease in the dust storm frequency. The intensified westerly jet stream over the northern Tibetan Plateau increases the dust storm frequency in the Taklimakan Desert. The positive geopotential height anomaly over Mongolia initiates an anticyclonic dust transport anomaly in the middle troposphere over northwestern China. It also induces a southeastward dust transport anomaly over North China. The reverse situations are true for a negative AO phase.

By using observations from the Aerosol Robotic Network (AERONET), aerosol types are classified according to dominant size mode and radiation absorptivity as determined by fine-mode fraction (FMF) and single-scattering albedo (SSA), respectively. The aerosol type from anthropogenic sources is significantly different with regard to location and season, while dust aerosol is observed persistently over North Africa and the Arabian Peninsula. For four reference locations where different aerosol types are observed, time series and optical properties for each aerosol type are investigated. The results show that aerosol types are strongly affected by their sources and partly affected by relative humidity. The analysis and methodology of this study can be used to compare aerosol classification results from satellite and chemical transport models, as well as to analyze aerosol characteristics on a global scale over land for which satellite observations need to be improved.

An aerosol retrieval algorithm for the first Geostationary Ocean Color Imager (GOCI) to be launched in March 2010 onboard the Communication, Ocean, and Meteorological Satellite (COMS) is presented. The algorithm retrieves aerosol optical depth (AOD), fine-mode fraction (FMF), and aerosol type in 500 m × 500 m resolution. All the products are retrieved over clear water which is defined by surface reflectance ratio between 640 nm and 860 nm (SRR) less or equal to 2.5, while only AOD is retrieved over turbid water (SRR > 2.5) due to high surface reflectance. To develop optimized algorithm for the target area of GOCI, optical properties of aerosol are analyzed from extensive observation of AERONET sunphotometers to generate lookup table. Surface reflectance of turbid water is determined from 30-day composite of Rayleigh- and gas corrected reflectance. By applying the present algorithm to MODIS top-of-the atmosphere reflectance, three different aerosol cases dominated by anthropogenic aerosol contains black carbon (BC), dust, and non-absorbing aerosol are analyzed to test the algorithm. The algorithm retrieves AOD, and size information together with aerosol type which are consistent with results inferred by RGB image in a qualitative way. The comparison of the retrieved AOD with those of MODIS collection 5 and AERONET sunphotometer observations shows reliable results. Especially, the application of turbid water algorithm significantly increases the accuracy in retrieving AOD at Anmyon station. The sensitivity study between MODIS and GOCI instruments in terms of relative sensitivity and scattering angle shows promising applicability of the present algorithm to future GOCI measurements.

The purpose of this study is to investigate the effects of precipitation physics in a general circulation model (GCM) on a simulated climate. Experiments are performed under the single column model (SCM) framework to examine basic features and under the general circulation model framework to investigate the impact on seasonal simulation. The SCM simulation shows that convection processes in the model have a considerable influence on the change in vertical thermodynamic structure, resulting in a change in precipitation, whereas in the GCM framework stratiform precipitation physics play a distinct role in changing the atmospheric structure. The GCM experiments also show that the overall reduction of precipitation in simulations with prognostic stratiform precipitation physics is highly related to changes in cloudiness and corresponding changes in radiative flux, which in turn leads to the reduction of convective activities.

Simultaneous measurements of gaseous species and fine-mode, particulate inorganic components were performed at the University of Seoul, Seoul in Korea. In the simultaneous measurements, a certain level of nitrous acid (HONO) was observed in the gas-phase, indicating possible heterogeneous HONO production on the surface of the ambient aerosols. On the other hand, high particulate nitrite (NO 2− ) concentrations of 1.41(±2.26) μg/m 3 were also measured, which sometimes reached 18.54 μg/m 3 . In contrast, low HONO-to-NO 2 ratios of 0.007(±0.006) were observed in Seoul. This indicates that a significant fraction of HONO is dissolved in atmospheric aerosols. Around the Seoul site, sufficient alkalinity may have been provided to the atmospheric aerosols from the excessive presence of NH 3 in the gas-phase. Due to the alkaline particulate conditions (defined in this study as a particle pH >∼3.29), the HONO molecules produced at the surface of the atmospheric aerosols appeared to have been converted into particulate nitrite, thereby preventing their further participation in the atmospheric O 3 /NO y /HO x photochemical cycles. It was estimated that a minimum average of 65% of HONO was captured by alkaline, anthropogenic, urban particles in the Seoul measurements.

In this work, we determine the major channels through which air pollutants, mainly originating in Northeast Asian mega-cities, flow out into the Northwestern Pacific atmosphere. For this purpose, comprehensive backward/forward trajectory analyses are conducted. Two important channels along which pollutants from the Northeast Asian mega-cities flow out are defined, and are labeled as “DC8 transport path” and “P3B transport path”. We then comprehensively examine the chemico-microphysical transformations of the anthropogenic pollutants from the Northeast Asian mega-cities along the two major transport paths, using a new Lagrangian forward-trajectory photochemical model. In the newly developed model, state-of-the-science parameterizations for considering chemico-microphysical aging processes and atmospheric aerosol processes are incorporated. As air masses travel toward low latitudes through the marine boundary layer (MBL), the temperature increases along the trajectories and large amounts of PAN experience thermal decomposition. By this process, PAN can be an important supplier of NO 2 in the remote MBL. The O 3 productions in the remote Northwestern Pacific MBL are fueled and maintained by NO x provided from the PAN decomposition. High O 3 levels (>50 ppb) are observed within the remote MBL of the Northwestern Pacific Oceans from several TRACE-P DC8 and P3B measurements under the continental outflow situations. Gas-phase SO 2 is continuously converted into nss-sulfate via heterogeneous oxidation reaction with H 2 O 2 at a particle pH of 2–5. The Lagrangian-trajectory modeling studies also indicate that in the remote MBL of Northwestern Pacific Ocean under continental outflow situations, conditions are unfavorable for nucleation events, because of the depletion of SO 2 , the large aerosol surface areas available for H 2 SO 4 sink, and high temperatures.

The Korea Sounding Rocket-III (KSR-III) was successfully launched on November 28, 2002 from the west coast of the Korean Peninsula. The science payload onboard the KSR-III included an ozone detector and two magnetometers along with other various sensors installed to measure physical characteristics such as temperature, pressure, strain, and acceleration. The main objective of KSR-III was to evaluate the liquid propulsion engine system which has been newly adopted in the KSR series. In addition to this main objective, the science payload conducted atmospheric soundings. The payload data were transmitted to the ground station in real time by an onboard telemetry system. The UV radiometer measured the direct solar UV radiation and during the ascending phase the vertical ozone density profile was obtained. This result was compared with coincident measurements taken by other satellites, a ground station, and an ozonesonde. A fluxgate-type magnetometer was onboard the KSR-III to observe the Earth's DC magnetic field and for AC field measurements, a search-coil magnetometer was installed. This was the first Korean mission to use magnetometers on a rocket-borne platform to measure the Earth's magnetic field. Using the telemetry magnetometer data, a study on the rocket attitude was carried out. This paper will give an overview of the design, calibration, and test results of the science payload onboard the KSR-III.

Extensive forest fire activities occurred in May 2003 across Siberia, Russia, particularly in the area between the Amur and Lena rivers east of Lake Baikal. These forest fires released large amounts of particulates and gases into the atmosphere, resulting in adverse effects on regional air quality and radiation budget. On certain occasions, a smoke pollution plume from these forest fires was transported through Mongolia and eastern China, down to the Korean peninsula. In this study, satellite data and ground-based radiation measurement data were analyzed to estimate the smoke aerosol's impact on the local atmospheric environment over Korea. Aerosol optical depth (AOD) values retrieved using the Bremen Aerosol Retrieval method from Moderate Resolution Imaging Spectroradiometer data were compared with those derived from ground-based radiation measurements. Large AOD values in the range 2.0–4.0 were observed on 20 May 2003 over Korea due to the influence of the long-range transported smoke aerosol plume from the Russian fires, resulting in a surface-observed short-wavelength direct aerosol radiative forcing efficiency of −90 to −200 W m −2 . This smoke aerosol plume also resulted in a decrease in the solar visible irradiance of up to 57%, and increased the surface PM10 concentration by up to 258 μg m −3 .

We have used a Fourier Transform Spectrometer (FTS) to study atmospheric waves in upper mesosphere over Chungwon.(36.6° N, 127° E), Korea. Measurements of the OH(3-1) bands were used to derive temperature and airglow intensity information of upper mesosphere. For this study, we analyzed OH measurements taken between April and June 2001, and performed spectral analysis to get wave information. We report characteristics of observed waves and compare the results with existing theoretical reports.

KSR-II, a two-stage sounding rocket of KARI was launched successfully at the Korean Peninsula on June 11, 1998. The apogee of the rocket was 137 km. For the ozone measurement, 8-channel UV and visible radiometers were onboard the rocket. The rocket measured an in situ stratospheric and mesospheric ozone density profile over Korea during its ascending phase using the radiometer and transmitted the data to ground station in real time. The maximum ozone density occurs near 25 km. Retrieved profile has a random error (1σ) of approximately 15% for altitude below 20km, 7% between 20-50 km and 10% greater than 50 km. The retrieved data were compared with Dobson spectrophotometer, ozonesonde, and HALOE onboard the UARS. Our results are in reasonable agreements with others.

A Michelson interferometer was used to observe the hydroxyl (OH) emission in the upper mesosphere at the King Sejong Station (62.22° S, 301.25° E), Antarctica. The instrument was installed in February 1999 and has been in routine operation since then. An intensive operational effort has resulted in a substantial data set between April and June, 1999. A spectral analysis was performed on individual data to examine the information of dominant waves. A harmonic analysis was also carried out on the monthly average data to investigate the characteristics of the major low frequency oscillations. The 12-hr temperature oscillations exhibit a striking agreement with a theoretical tidal model, supporting the tidal (migrating) origin. The 8-hr wave is found to be persistent and dominant, reflecting its major role in the upper mesospheric dynamics at the given latitude. The 6-hr oscillation is observed only in May with its value close to the prediction for zonally symmetric tides.