Jason Andrew Miech

Volatile organic compounds (VOCs) are key precursors of ozone and secondary organic aerosol, yet wintertime constraints on how local emissions, chemical lifetime, and regional transport jointly shape VOC distributions over Korea and the Yellow Sea remain limited based on airborne measurements. We analyzed proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) measurements from 17 Beechcraft 1900D flights during the 2024 Airborne and Satellite Investigation of Asian Air Quality (ASIA-AQ) campaign. The sum of seven VOC species or groups was 2.4 times higher over Seoul than over the Yellow Sea. Toluene, C₈ aromatics, and a methyl ethyl ketone (MEK)-equivalent signal were strongly enhanced in low-altitude, source-influenced air masses, whereas benzene, acetone, and acetonitrile showed weaker regional and vertical contrasts. Seoul-to-Yellow Sea VOC-to-benzene slope ratios generally increased with chemical reactivity, but toluene and C₈ aromatics showed positive deviations, indicating an additional influence of urban aromatic source composition. Yellow Sea observations, supported by NASA DC-8 measurements, indicated continental outflow. An order-of-magnitude transport analysis estimated distance scaled Yellow Sea transport equivalents of approximately 30 % of Seoul benzene emissions in the Clean Air Policy Support System inventory and 6 % for toluene. Wintertime VOC variability is thus species dependent: urban and industrial emissions dominate reactive aromatic VOCs, whereas longer-lived benzene is more sensitive to regional transport. Effective wintertime VOC management requires species-specific strategies considering domestic emissions and regional inflow.

Nitrous oxide (N ₂ O) is the most dominant precursor of ozone-depleting substances and the third most important anthropogenic greenhouse gas, with agriculture contributing the largest share of emissions (56 %). Over the past two decades, airborne in-situ measurements have become increasingly important for studying emission and transport of N ₂ O in the atmosphere, also driven by the development of more precise and simultaneously faster Quantum Cascade Laser (QCL)-based spectrometers. However, many QCL-based spectrometers exhibit sensitivities to environmental and flight-related parameters that can vary rapidly (≤ 1 s), such as static or cabin pressure and aircraft roll and pitch angles. The impact of changing ambient water vapor is particularly critical due to both dilution and quantum-mechanical effects. Because the variability of N ₂ O in the lower troposphere is often very small (< 1 ppb) relative to its high background (∼ 338 ppb), even minor variations in these parameters can significantly affect data quality and must be corrected. Although many instruments can resolve such small concentration changes, their typical temporal resolution of 1 Hz may limit the application of advanced measurement techniques such as eddy covariance on fast-moving aircraft. Here, we present and evaluate a new instrument setup for precise (< 0.2 ppb) and high-frequency (10 Hz) airborne in-situ N ₂ O measurements in altitudes up to 4500 m based on a MIRO MGA ³ QCL spectrometer (MIRO Analytical AG). The instrument was successfully deployed during two airborne science missions, namely onboard the unpressurized DLR Cessna during the Greenhouse Gas Monitoring (GHGMon) campaign in 2023 in the Netherlands, as well as onboard the NASA DC-8 during the Airborne and Satellite Investigation of Asian Air Quality (ASIA-AQ) campaign in 2024. Specifically, we evaluate and compare different water vapor correction approaches using ASIA-AQ data sampled within the tropical boundary layer over South Korea, the Philippines, Thailand and Taiwan, which partly were characterized by specifically high ambient humidity (up to 30 000 ppm H ₂ O). The water vapor correction methods include an empirical approach that relies on both native and corrected MIRO in-flight water vapor measurements, as well as an approach by an updated version of the MIRO specific fitting software. Comparison with N ₂ O measurements from a well-established instrument onboard the NASA DC-8 shows agreement within combined measurement uncertainties for all tested water vapor correction approaches, albeit special caution is needed for humidities larger than 15 000 ppm. The new water vapor corrected data shows a 42 % better precision than with original default settings of the instrument. We further show that the instrument setup is insensitive to flight parameter changes such as roll and pitch angle of the aircraft, and allows for stable measurements even under challenging conditions such as in the turbulent boundary layer. This instrument setup enables improved characterization of N ₂ O emissions and sources from the agricultural sector, which is particularly relevant for tropical regions with strong agricultural activity and high humidity, where observational data remain scarce.

Asia accounts for approximately half of global anthropogenic emissions of major pollutants, yet emission inventories remain uncertain and ground-based monitoring is sparse across much of the region. To address these challenges, this study applies a multi-species satellite data assimilation framework to estimate emissions and concentrations of key chemical species during the NASA's ASIA-AQ campaign. The assimilation improves agreement with airborne observations for O₃, NO_x, CO, and CH₂O, with the largest gains for CO (correlation increasing from 0.63–0.64 to 0.77) and CH₂O (biases reduced by 41–70 %). Domain-wide, the optimized emissions show increases of 15 % for NO_x and 9 % for CO, and a 52 % reduction in isoprene. Comparisons with multiple emission inventories reveal large discrepancies, with normalized standard deviation ranging from 11 % for NO_x in mainland China to 68 % for CO in Taiwan. Over Thailand, the assimilation increases fire emissions from 3.6 Tg (GFASv1.2) to 8.3 Tg, while FINNv2.7 produces estimates roughly twice as high, highlighting persistent divergence among fire emission estimates. Source-receptor analysis reveals strong meteorological control on transboundary pollutant: long-range transport contributes up to 62 % of surface O₃ in Manila during strong monsoon conditions, whereas Seoul exhibits local NO_x-saturated chemistry. During a strong transport episode, Indian emissions account for 72–78 % of the free tropospheric O₃ response over Taipei and Chiang Mai, and 24 % over Seoul, highlighting an overlooked transport pathway affecting Asian air quality. These results highlight the value of satellite data assimilation and the need for improved inventories and coordinated action on local and transboundary pollution.

Nitrous oxide (N₂O) is the most dominant precursor of ozone-depleting substances and the third most important anthropogenic greenhouse gas, with agriculture contributing the largest share of emissions (56 %). Over the past two decades, airborne in-situ measurements have become increasingly important for studying emission and transport of N₂O in the atmosphere, also driven by the development of more precise and simultaneously faster Quantum Cascade Laser (QCL)-based spectrometers. However, many QCL-based spectrometers exhibit sensitivities to environmental and flight-related parameters that can vary rapidly (≤ 1 s), such as static or cabin pressure and aircraft roll and pitch angles. The impact of changing ambient water vapor is particularly critical due to both dilution and quantum-mechanical effects. Because the variability of N₂O in the lower troposphere is often very small (2O measurements in altitudes up to 4500 m based on a MIRO MGA³ QCL spectrometer (MIRO Analytical AG). The instrument was successfully deployed during two airborne science missions, namely onboard the unpressurized DLR Cessna during the Greenhouse Gas Monitoring (GHGMon) campaign in 2023 in the Netherlands, as well as onboard the NASA DC8 during the Satellite Investigation of the Asian Air Quality (ASIA-AQ) campaign in 2024. Specifically, we evaluate and compare different water vapor correction approaches using ASIA-AQ data sampled within the tropical boundary layer over South Korea, the Philippines, Thailand and Taiwan, which partly were characterized by specifically high ambient humidity (up to 30000 ppm H₂O). The water vapor correction methods include an empirical approach that relies on both native and corrected MIRO in-flight water vapor measurements, as well as an approach by an updated version of the MIRO specific fitting software. Comparison with N₂O measurements from a well-established instrument onboard the NASA DC8 shows agreement within combined measurement uncertainties for all tested water vapor correction approaches, albeit special caution is needed for humidities larger than 15000 ppm. The new water vapor corrected data shows a 42 % better precision than with original default settings of the instrument. We further show that the instrument setup is insensitive to flight parameter changes such as roll and pitch angle of the aircraft, and allows for stable measurements even under challenging conditions such as in the turbulent boundary layer. This instrument setup enables improved characterization of N₂O emissions and sources from the agricultural sector which is, in particular, relevant for tropical regions with strong agricultural activity and high humidity, where observational data remain scarce.

Nitrous oxide (N₂O) is the most dominant precursor of ozone-depleting substances and the third most important anthropogenic greenhouse gas, with agriculture contributing the largest share of emissions (56 %). Over the past two decades, airborne in-situ measurements have become increasingly important for studying emission and transport of N₂O in the atmosphere, also driven by the development of more precise and simultaneously faster Quantum Cascade Laser (QCL)-based spectrometers. However, many QCL-based spectrometers exhibit sensitivities to environmental and flight-related parameters that can vary rapidly (≤ 1 s), such as static or cabin pressure and aircraft roll and pitch angles. The impact of changing ambient water vapor is particularly critical due to both dilution and quantum-mechanical effects. Because the variability of N₂O in the lower troposphere is often very small (2O measurements in altitudes up to 4500 m based on a MIRO MGA³ QCL spectrometer (MIRO Analytical AG). The instrument was successfully deployed during two airborne science missions, namely onboard the unpressurized DLR Cessna during the Greenhouse Gas Monitoring (GHGMon) campaign in 2023 in the Netherlands, as well as onboard the NASA DC8 during the Satellite Investigation of the Asian Air Quality (ASIA-AQ) campaign in 2024. Specifically, we evaluate and compare different water vapor correction approaches using ASIA-AQ data sampled within the tropical boundary layer over South Korea, the Philippines, Thailand and Taiwan, which partly were characterized by specifically high ambient humidity (up to 30000 ppm H₂O). The water vapor correction methods include an empirical approach that relies on both native and corrected MIRO in-flight water vapor measurements, as well as an approach by an updated version of the MIRO specific fitting software. Comparison with N₂O measurements from a well-established instrument onboard the NASA DC8 shows agreement within combined measurement uncertainties for all tested water vapor correction approaches, albeit special caution is needed for humidities larger than 15000 ppm. The new water vapor corrected data shows a 42 % better precision than with original default settings of the instrument. We further show that the instrument setup is insensitive to flight parameter changes such as roll and pitch angle of the aircraft, and allows for stable measurements even under challenging conditions such as in the turbulent boundary layer. This instrument setup enables improved characterization of N₂O emissions and sources from the agricultural sector which is, in particular, relevant for tropical regions with strong agricultural activity and high humidity, where observational data remain scarce.

Nitrous oxide (N₂O) is the most dominant precursor of ozone-depleting substances and the third most important anthropogenic greenhouse gas, with agriculture contributing the largest share of emissions (56 %). Over the past two decades, airborne in-situ measurements have become increasingly important for studying emission and transport of N₂O in the atmosphere, also driven by the development of more precise and simultaneously faster Quantum Cascade Laser (QCL)-based spectrometers. However, many QCL-based spectrometers exhibit sensitivities to environmental and flight-related parameters that can vary rapidly (≤ 1 s), such as static or cabin pressure and aircraft roll and pitch angles. The impact of changing ambient water vapor is particularly critical due to both dilution and quantum-mechanical effects. Because the variability of N₂O in the lower troposphere is often very small (2O measurements in altitudes up to 4500 m based on a MIRO MGA³ QCL spectrometer (MIRO Analytical AG). The instrument was successfully deployed during two airborne science missions, namely onboard the unpressurized DLR Cessna during the Greenhouse Gas Monitoring (GHGMon) campaign in 2023 in the Netherlands, as well as onboard the NASA DC8 during the Satellite Investigation of the Asian Air Quality (ASIA-AQ) campaign in 2024. Specifically, we evaluate and compare different water vapor correction approaches using ASIA-AQ data sampled within the tropical boundary layer over South Korea, the Philippines, Thailand and Taiwan, which partly were characterized by specifically high ambient humidity (up to 30000 ppm H₂O). The water vapor correction methods include an empirical approach that relies on both native and corrected MIRO in-flight water vapor measurements, as well as an approach by an updated version of the MIRO specific fitting software. Comparison with N₂O measurements from a well-established instrument onboard the NASA DC8 shows agreement within combined measurement uncertainties for all tested water vapor correction approaches, albeit special caution is needed for humidities larger than 15000 ppm. The new water vapor corrected data shows a 42 % better precision than with original default settings of the instrument. We further show that the instrument setup is insensitive to flight parameter changes such as roll and pitch angle of the aircraft, and allows for stable measurements even under challenging conditions such as in the turbulent boundary layer. This instrument setup enables improved characterization of N₂O emissions and sources from the agricultural sector which is, in particular, relevant for tropical regions with strong agricultural activity and high humidity, where observational data remain scarce.

Wintertime photochemical air pollution in East Asia remains poorly constrained despite its impact on regional air quality. Sources and formation pathways of acyl peroxynitrates (PANs) and ozone (O₃), key photochemical products, are not well understood, hindering effective mitigation strategies. We investigate PANs and O₃ over South Korea using observations from the ASIA-AQ campaign (February–March 2024). PANs reached 5.5 ppbv, strongly correlating with formaldehyde and particulate matter, indicating active winter photochemistry. Median PANs were higher in the mid-southern peninsula (MS; 990 pptv) and Yellow Sea (1200 pptv) than the Seoul Metropolitan Area (840 pptv). Elevated homologue-to-acetyl peroxynitrate ratios over the MS, with enhanced acryloyl peroxynitrate, acrolein, and ethylene oxide, provided tracers for petrochemical emissions and their impacts. Acetaldehyde contributed 53 %–80 % of PAN production. Ethanol was a major precursor of acetaldehyde (∼ 50 %). Strong correlations (r² > 0.8) of ethanol and halocarbons indicate industrial and solvent sources under-represented in inventories. Formaldehyde and C₂₊ aldehydes contributed ∼ 30 % to ozone production. Low ozone production efficiency (< 10) and radical termination dominated by nitric acid and PANs (> 80 %) indicate VOC-limited conditions. The fractional PANs contribution to NO_x loss increased with decreasing OH reactivity ratio of NO₂ to aldehydes, suggesting spatial increases in ozone production following NO_x reductions. These findings demonstrate that a comprehensive understanding of VOC oxidation, particularly oxygenates from industrial sources, is essential for representing winter photochemistry. PANs measurements provide critical constraints on oxidation processes and their implications for emission control.

Nitrous oxide (N₂O) is the most dominant precursor of ozone-depleting substances and the third most important anthropogenic greenhouse gas, with agriculture contributing the largest share of emissions (56 %). Over the past two decades, airborne in-situ measurements have become increasingly important for studying emission and transport of N₂O in the atmosphere, also driven by the development of more precise and simultaneously faster Quantum Cascade Laser (QCL)-based spectrometers. However, many QCL-based spectrometers exhibit sensitivities to environmental and flight-related parameters that can vary rapidly (≤ 1 s), such as static or cabin pressure and aircraft roll and pitch angles. The impact of changing ambient water vapor is particularly critical due to both dilution and quantum-mechanical effects. Because the variability of N₂O in the lower troposphere is often very small (2O measurements in altitudes up to 4500 m based on a MIRO MGA³ QCL spectrometer (MIRO Analytical AG). The instrument was successfully deployed during two airborne science missions, namely onboard the unpressurized DLR Cessna during the Greenhouse Gas Monitoring (GHGMon) campaign in 2023 in the Netherlands, as well as onboard the NASA DC8 during the Satellite Investigation of the Asian Air Quality (ASIA-AQ) campaign in 2024. Specifically, we evaluate and compare different water vapor correction approaches using ASIA-AQ data sampled within the tropical boundary layer over South Korea, the Philippines, Thailand and Taiwan, which partly were characterized by specifically high ambient humidity (up to 30000 ppm H₂O). The water vapor correction methods include an empirical approach that relies on both native and corrected MIRO in-flight water vapor measurements, as well as an approach by an updated version of the MIRO specific fitting software. Comparison with N₂O measurements from a well-established instrument onboard the NASA DC8 shows agreement within combined measurement uncertainties for all tested water vapor correction approaches, albeit special caution is needed for humidities larger than 15000 ppm. The new water vapor corrected data shows a 42 % better precision than with original default settings of the instrument. We further show that the instrument setup is insensitive to flight parameter changes such as roll and pitch angle of the aircraft, and allows for stable measurements even under challenging conditions such as in the turbulent boundary layer. This instrument setup enables improved characterization of N₂O emissions and sources from the agricultural sector which is, in particular, relevant for tropical regions with strong agricultural activity and high humidity, where observational data remain scarce.