The Korea-United States Air Quality (KORUS-AQ) field study

Abstract

The Korea-United States Air Quality (KORUS-AQ) field study was conducted during May-June 2016. The effort was jointly sponsored by the National Institute of Environmental Research of South Korea and the National Aeronautics and Space Administration of the United States. KORUS-AQ offered an unprecedented, multi-perspective view of air quality conditions in South Korea by employing observations from three aircraft, an extensive ground-based network, and three ships along with an array of air quality forecast models. Information gathered during the study is contributing to an improved understanding of the factors controlling air quality in South Korea. The study also provided a valuable test bed for future air quality-observing strategies involving geostationary satellite instruments being launched by both countries to examine air quality throughout the day over Asia and North America. This article presents details on the KORUS-AQ observational assets, study execution, data products, and air quality conditions observed during the study. High-level findings from companion papers in this special issue are also summarized and discussed in relation to the factors controlling fine particle and ozone pollution, current emissions and source apportionment, and expectations for the role of satellite observations in the future. Resulting policy recommendations and advice regarding plans going forward are summarized. These results provide an important update to early feedback previously provided in a Rapid Science Synthesis Report produced for South Korean policy makers in 2017 and form the basis for the Final Science Synthesis Report delivered in 2020.

Keywords: Air quality; KORUS-AQ; Ozone; PM2.5; Seoul; Transboundary pollution.

Figure 1.

Schematic representation of the observing strategy used to address Korea–United States Air Quality science goals and explore the synergy between multi-perspective observations from the ground, air, and space. Details for each listed asset are provided in the text. DOI: https://doi.org/10.1525/elementa.2020.00163.f1

Figure 2.

Ground-based observations during the Korea–United States Air Quality field study included (a) monitors comprising the AirKorea monitoring network and (b) research sites incorporating combinations of in situ observations (red), Pandora spectrometers (green), and AERONET sunphotometers (blue). Panel (c) offers an expanded view of sites located in the Seoul Metropolitan Area. Details on ground observations at these sites are provided in Tables 1–4. DOI: https://doi.org/10.1525/elementa.2020.00163.f2

Figure 3.

Google Earth images are overlaid with flight tracks for each of the Korea–United States Air Quality aircraft. Special Use Airspace affecting flight access is overlaid with circles representing airports and polygons representing military operations areas (white), restricted areas (teal), and prohibited areas (magenta). Expanded views of flight patterns conducted over the Seoul Metropolitan Area by each aircraft are shown in the bottom images with the Seoul City Boundary (white line) and research sites at Olympic Park (red) and Taehwa Forest (orange) marked. DOI: https://doi.org/10.1525/elementa.2020.00163.f3

Figure 4.

Daily statistics for (a) ozone and (b) PM_2.5 observed across the AirKorea monitoring network during the Korea-United States Air Quality field study. Box whisker plots indicate the median, interquartile range, and 5th and 95th percentiles. Flight days are shown in green. Red lines indicate the air quality standards in place at the time of the study. The dashed line signifies the more recent tightening of standards for PM_2.5. DOI: https://doi.org/10.1525/elementa.2020.00163.f4

Figure 5.

Ceilometer (CL51) normalized backscatter images of the lower atmosphere (0–4,500 m) over Olympic Park from May 8 to 31, 2016. Black and red lines indicate backscatter gradients associated with mixed layer and residual layer heights diagnosed from the CL51 BL-View 1.0 graphical interface with statistical filter applied (Knepp et al., 2017). The white line shows variability in hourly-average PM_2.5 (0–90 μg/m³) for AirKorea monitors in Seoul. DOI: https://doi.org/10.1525/elementa.2020.00163.f5

Figure 6.

Vertical distribution of ozone observed by the DC-8 during 52 profiles conducted over the Seoul Metropolitan Area east of the Taehwa Research Forest site. Boxes showing median and inner quartile values for 1 km increments of altitude are plotted over the individual measurements separated into morning, midday, and afternoon observations. DOI: https://doi.org/10.1525/elementa.2020.00163.f6

Figure 7.

Geostationary Trace gas and Aerosol Sensor Optimization (GeoTASO) mapping of NO₂ and CH₂O vertical column densities across the Seoul Metropolitan Area throughout the day on June 9, 2016. DOI: https://doi.org/10.1525/elementa.2020.00163.f7

Figure 8.

Diurnal statistics for multi-perspective observations of NO₂ and CH₂O at Olympic Park. Median and interquartile ranges are shown for hourly in situ surface measurements, hourly Pandora column densities (NO₂ only), and in situ vertical profiles from the DC-8 for morning, midday, and afternoon overflights. DOI: https://doi.org/10.1525/elementa.2020.00163.f8