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

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.

Improved methods for performing multivariate analysis and deriving background spectra in atmospheric open-path FT-IR monitoring.

Open-path Fourier transform infrared spectrometry (OP/FT-IR) may improve the temporal and spatial resolution in air pollutant measurements compared to conventional sampling methods. However, a successful OP/FT-IR operation requires an experienced analyst to resolve chemical interference as well as to derive a suitable background spectrum. The present study aims at developing a systematic method of handling the OP/FT-IR derived spectra for the measurement of photochemical oxidants and volatile organic compounds (VOCs) in urban areas. A classical least-squares (CLS) method, the most frequently used regression method in OP/FT-IR, is modified to constrain all the analyzed chemical species concentrations within a physically reasonable range. This new CLS method, named constrained CLS, may save the effort of predetermining the chemical species to be analyzed. A new background spectrum generation method is also introduced to more efficiently handle chemical interferences. Finally, CLS is shown to be prone to propagating errors in the case that a few data points contain a significant amount of error. The LI-norm minimization method reduces this error propagation to considerably increase the stability compared to CLS. The presently developed analysis software based on these approaches is compared with the other conventional CLS method using an artificially made single-beam spectrum as well as a field single-beam spectrum.