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 SO2, NO2, CO, and PM10 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 SO2 and PM10 from eastern China were higher than those of NO2 and CO. The mean concentrations of SO2, NO2, CO, and PM10 in Seoul for the period from 2001 to 2014 were 5.34, 37.0, and 619.1 ppb, and 57.4 4 μg/m3, respectively. The contributions of long-range transport to the mean concentrations of SO2, NO2, CO, and PM10 in Seoul were 0.74, 3.4, and 39.0 ppb, and 12.1 μg/m3, respectively, which are 14%, 9%, 6%, and 21% of the mean concentrations, respectively. The annual mean concentrations of SO2 and NO2 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 PM10 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 SO2, NO2, CO, and PM10 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.
•The long-range transports of pollutants to Seoul were analyzed from 2001 to 2014.•Long-range transport increase SO2, NO2, CO, PM10 concentration by 14%, 9%, 6%, 21%.•Transports from near Beijing and Harbin are becoming more significant recently.
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.
•Geostationary satellite well monitors the LRTT of aerosol plumes.•High AOD in South Korea coincides with the AOD enhancement in east-central China.•When the westerly is slower, Korean domestic emissions affect local air quality more.
Formaldehyde (HCHO) in the ambient air not only causes cancer but is also an ideal
indicator of volatile organic compounds (VOCs), which are major precursors of
ozone (O3) and secondary organic ...aerosol (SOA) near the surface. It
is meaningful to differentiate between the direct emission and the secondary
formation of HCHO for HCHO pollution control and sensitivity studies of
O3 production. However, understanding of the sources of HCHO is
still poor in China, due to the scarcity of field measurements (both
spatially and temporally). In this study, tropospheric HCHO vertical column
densities (VCDs) in the Yangtze River Delta (YRD), East China, where HCHO
pollution is serious, were retrieved from the Ozone Mapping and Profiler
Suite (OMPS) onboard the Suomi National Polar-orbiting Partnership
(Suomi-NPP) satellite from 2014 to 2017; these retrievals showed good
agreement with the tropospheric HCHO columns measured using ground-based
high-resolution Fourier transform infrared spectrometry (FTS) with a
correlation coefficient (R) of 0.78. Based on these results, the cancer
risk was estimated both nationwide and in the YRD region. It was calculated
that at least 7840 people in the YRD region would develop cancer in their
lives due to outdoor HCHO exposure, which comprised 23.4 % of total
national cancer risk. Furthermore, the contributions of primary and secondary
sources were apportioned, in addition to primary and secondary tracers from
surface observations. Overall, the HCHO from secondary formation contributed
most to ambient HCHO and can be regarded as the indicator of VOC reactivity
in Hangzhou and in urban areas of Nanjing and Shanghai from 2015 to 2017, due
to the strong correlation between total HCHO and secondary HCHO. At
industrial sites in Nanjing, primary emissions more strongly influenced
ambient HCHO concentrations in 2015 and showed an obvious decreasing trend.
Seasonally, HCHO from secondary formation reached a maximum in summer and a
minimum in winter. In the spring, summer, and autumn, secondary formation had
a significant effect on the variation of ambient HCHO in urban regions of
Nanjing, Hangzhou, and Shanghai, whereas in the winter the contribution from
secondary formation became less significant. A more thorough understanding of
the variation of the primary and secondary contributions of ambient HCHO is
needed to develop a better knowledge regarding the role of HCHO in
atmospheric chemistry and to formulate effective control measures to decrease
HCHO pollution and the associated cancer risk.
Long-term exposure to particulate matter (PM) with aerodynamic
diameters < 10 (PM10) and 2.5 µm (PM2.5) has
negative effects on human health. Although station-based PM monitoring has
been conducted ...around the world, it is still challenging to provide spatially
continuous PM information for vast areas at high spatial resolution.
Satellite-derived aerosol information such as aerosol optical depth (AOD) has
been frequently used to investigate ground-level PM concentrations. In this
study, we combined multiple satellite-derived products including AOD with
model-based meteorological parameters (i.e., dew-point temperature, wind
speed, surface pressure, planetary boundary layer height, and relative
humidity) and emission parameters (i.e., NO, NH3, SO2,
primary organic aerosol (POA), and HCHO) to estimate surface PM concentrations over South Korea. Random
forest (RF) machine learning was used to estimate both PM10 and
PM2.5 concentrations with a total of 32 parameters for 2015–2016. The
results show that the RF-based models produced good performance resulting in
R2 values of 0.78 and 0.73 and root mean square errors (RMSEs) of 17.08 and
8.25 µg m−3 for PM10 and
PM2.5, respectively. In particular, the proposed models successfully
estimated high PM concentrations. AOD was identified as the most significant
for estimating ground-level PM concentrations, followed by wind speed, solar
radiation, and dew-point temperature. The use of aerosol information derived
from a geostationary satellite sensor (i.e., Geostationary Ocean Color Imager, GOCI) resulted in slightly
higher accuracy for estimating PM concentrations than that from a
polar-orbiting sensor system (i.e., the Moderate Resolution
Imaging Spectroradiometer, MODIS). The proposed RF models yielded
better performance than the process-based approaches, particularly in
improving on the underestimation of the process-based models (i.e., GEOS-Chem
and the Community Multiscale Air Quality Modeling System, CMAQ).
Himawari-8, a next-generation geostationary meteorological satellite, was successfully launched by the Japanese Meteorological Agency (JMA) on 7 October 2014 and has been in official operation since ...7 July 2015. The Advanced Himawari Imager (AHI) onboard Himawari-8 has 16 channels from 0.47 to 13.3 μm and performs full-disk observations every 10 min. This study describes AHI aerosol optical property (AOP) retrieval based on a multi-channel algorithm using three visible and one near-infrared channels (470, 510, 640, and 860 nm). AOPs were retrieved by obtaining the visible surface reflectance using shortwave infrared (SWIR) data along with normalized difference vegetation index shortwave infrared (NDVISWIR) categories and the minimum reflectance method (MRM). Estimated surface reflectance from SWIR (ESR) tends to be overestimated in urban and cropland areas. Thus, the visible surface reflectance was improved by considering urbanization effects. Ocean surface reflectance is obtained using MRM, while it is from the Cox and Munk method in ESR with the consideration of chlorophyll-a concentration. Based on validation with ground-based sun-photometer measurements from Aerosol Robotic Network (AERONET) data, the error pattern tends to the opposition between MRMver (using MRM reflectance) AOD and ESRver (Using ESR reflectance) AOD over land. To estimate optimal AOD products, two methods were used to merge the data. The final aerosol products and the two surface reflectances were merged, which resulted in higher accuracy AOD values than those retrieved by either individual method. All four AODs shown in this study show accurate diurnal variation compared with AERONET, but the optimum AOD changes depending on observation time.
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.
•AOD retrievals from two types of satellites were assimilated solely.•Assimilating different AOD produced prominent geographic differences on forecast.•Larger increment under stable meteorological conditions lead to a longer duration.•The results emphasize the potential of combining different AOD retrievals.
By using multiple satellite measurements, the changes of the aerosol optical depth (AOD) and nitrogen dioxide (NO
) over South Korea were investigated from January to March 2020 to evaluate the ...COVID-19 effect on the regional air quality. The NO
decrease in South Korea was found but not significant, which indicates the effects of spontaneous social distancing under the maintenance of ordinary life. The AODs in 2020 were normally high in January, but they became lower starting from February. Since the atmosphere over Eastern Asia was unusually stagnant in January and February 2020, the AOD decrease in February 2020 clearly reveals the positive effect of the COVID-19. Considering the insignificant NO
decrease in South Korea and the relatively long lifetime of aerosols, the AOD decrease in South Korea may be more attributed to the improvement of the air quality in neighboring countries. In March, regional atmosphere became well mixed and ventilated over South Korea, contributing to large enhancement of air quality. While the social activity was reduced after the COVID-19 outbreak, the regional meteorology should be also examined significantly to avoid the biased evaluation of the social impact on the change of the regional air quality.
Planned geostationary satellites will provide aerosol optical depth (AOD) retrievals at high temporal and spatial resolution which will be incorporated into current assimilation systems that use ...low‐Earth orbiting (e.g., Moderate Resolution Imaging Spectroradiometer (MODIS)) AOD. The impacts of such additions are explored in a real case scenario using AOD from the Geostationary Ocean Color Imager (GOCI) on board of the Communication, Ocean, and Meteorology Satellite, a geostationary satellite observing northeast Asia. The addition of GOCI AOD into the assimilation system generated positive impacts, which were found to be substantial in comparison to only assimilating MODIS AOD. We found that GOCI AOD can help significantly to improve surface air quality simulations in Korea for dust, biomass burning smoke, and anthropogenic pollution episodes when the model represents the extent of the pollution episodes and retrievals are not contaminated by clouds. We anticipate future geostationary missions to considerably contribute to air quality forecasting and provide better reanalyses for health assessments and climate studies.
Key Points
Geostationary AOD data improves skill of current air quality predictionsImprovements are found for multiple types of pollution events on Northeast AsiaIt serves as a real case scenario support for planned geostationary missions
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.
Abstract
In 2019, an unusually strong positive Indian Ocean Dipole spawned hot and dry weather in southeastern Australia, which promoted devastating wildfires in the period from September 2019 to ...February 2020. The fires produced large plumes of biomass burning aerosols that prevented sunlight from reaching the Earth’s surface, and in this way elicited regional radiative cooling. We estimated the direct aerosol radiative forcing (ARF) resulting from these wildfires, based on Moderate Resolution Imaging Spectroradiometer space-based data and an empirical relationship from AErosol RObotic NETwork ground-based data collected in biomass-burning regions. The wildfire-derived air pollution was associated with an aerosol optical thickness of >0.3 in Victoria and a strongly negative ARF of between −14.8 and −17.7 W m
−2
, which decreased the surface air temperature by about 3.7 °C–4.4 °C. This is of the same order of magnitude as the radiative cooling from volcanic eruptions. Although the atmospheric lifetime of biomass-burning aerosols is relatively short (about a week), the Australian wildfire pollution plumes extended across the Pacific Ocean to South America. Since climate change is expected to lead to more frequent and increasingly intense fires in many regions worldwide, the consequent biomass burning aerosols may become a significant radiative forcing factor, which will need to be accounted for in climate model projections for the future.
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