Thomas F. Hanisco

In recent years, significant perturbations to stratospheric inorganic chlorine have been observed following wildfires or volcanic eruptions, as well as modeled in simulations with elevated water vapor from overshooting convection or organic species in biomass burning aerosol. A detailed evaluation of inorganic chlorine in the stratosphere sampled under various conditions is presented here using high precision in situ aircraft measurements of chlorine monoxide (ClO) and chlorine nitrate (ClONO₂). Data were obtained over North America during the NASA Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) mission. The vertical distributions of ClO and ClONO₂ from all 29 research flights of the 2-year mission are found to be relatively compact and lacking substantial outliers. The peak mixing ratios are approximately 30 ppt and 400 ppt for ClO and ClONO₂, respectively. No chlorine activation was observed in the lower stratosphere in the presence of low temperatures and elevated water vapor from convective injection. Steady-state calculated ClONO₂ is found to be in good agreement with measured values, suggesting that a reduction in the uncertainty of the recommended rate coefficient for ClONO₂ production is possible. HCl is calculated at high time resolution throughout the mission using satellite data, and the resulting evaluation of the inorganic chlorine budget shows excellent agreement, with the ratio of ClO + ClONO₂ + HCl to total inorganic chlorine equal to 0.95 for mixing ratios greater than 500 ppt. No evidence of inorganic chlorine activation was observed during DCOTSS when aerosol organic mass fraction and biomass burning fraction were elevated.

Total column ozone (TCO) has been observed since the 1920s, with a systematic monitoring network established during the International Geophysical Year (1957–1958). We compile and assess TCO records from six major ground-based instrument types: Dobson and Brewer spectrophotometers, Filter ozonometers, zenith-sky DOAS (UVVIS), Fourier-transform infrared (FTIR) spectroscopy, and Pandora spectrometers. Data are drawn from the World Ozone and Ultraviolet Radiation Data Centre, Network for the Detection of Atmospheric Composition Change, Pandonia Global Network, and European Brewer Network. Using harmonized statistical criteria and daily comparisons with multiple satellite products and four reanalysis datasets, we evaluate site-level performance in 5-year intervals from 1940 to 2024. Metrics include mean bias, variability of daily and monthly differences, seasonal amplitude, and the range of annual means, with percentile-based thresholds used to classify data quality. Ground-based annual means generally agree with satellite and reanalysis benchmarks within ± 2 %, with typical variability near 2 %. Larger discrepancies occur in the pre-satellite era, where reanalyses show biases of up to −5 % relative to Dobson observations. Network-wide distributions of daily mean differences to those from reanalysis and satellite data indicate comparable internal consistency for Brewer, Dobson, FTIR, and Pandora (standard deviations generally around 2 %), while Filter and UVVIS exhibit slightly broader spreads (< 3 %), especially at high latitudes. Network capacity has evolved substantially since the 2000s, with a decline in Dobson sites and expansion of Brewer and Pandora observations. By providing station-level flags and thresholds, this assessment helps network operators prioritize calibration and reprocessing efforts and helps users identify robust records, thereby improving confidence in long-term ozone trend detection and satellite validation.

The U.S. Gulf Coast (Gulf) Outer Continental Shelf (OCS) is a region of extensive offshore oil and natural gas (ONG) activity, where nitrogen oxides (NO _x ) emissions contribute to regional air quality and ozone formation. However, offshore surface observations are limited, making satellite-based measurements essential for characterizing nitrogen dioxide (NO₂) patterns and variability. The launch of the Tropospheric Emissions: Monitoring of Pollution (TEMPO) geostationary instrument in 2023 provides hourly NO₂ observations over North America, including the Gulf OCS region. Building on findings from the first Satellite Coastal and Oceanic Atmospheric Pollution Experiment (SCOAPE) campaign (May 2019), this study evaluates TEMPO NO₂ retrievals using coordinated observations from SCOAPE-II (June and October 2024): ship-based in-situ measurements, Pandora total column NO₂, and airborne GEOstationary Coastal and Air Pollution Events (GEO-CAPE) Airborne Simulator (GCAS) observations. Results indicate that TEMPO shows moderate agreement with Pandora observations, with correlation coefficients (r) below 0.5 during the campaign and mean absolute percent differences of 16% over land and 23% over water. At a coastal monitoring site in Cameron, Louisiana, TEMPO exhibits a systematic positive bias of ~10% relative to Pandora while capturing similar temporal variability and improved correlation (R = 0.61) for August 2023–December 2024. Over offshore regions, TEMPO diurnal patterns are weaker than land, reflecting lower NO₂ amounts and increased retrieval uncertainty. Airborne GCAS observations demonstrate that TEMPO can detect NO₂ enhancements associated with offshore platforms and drill ships, though its spatial resolution limits representation of fine-scale plume structure.

Pandora formaldehyde (HCHO) retrievals in the boundary layer provide continuous observations of HCHO vertical distribution, yet validation of these retrievals remains limited. This work evaluates Pandora retrievals of the vertical distribution of formaldehyde (HCHO) against aircraft in situ measurements collected at four U.S. East Coast sites during the summers of 2024 and 2025. Tropospheric columns and vertical profiles are consistent with aircraft-based observations within measurement uncertainty, with agreement that depends critically on the alignment between the Pandora viewing geometry and local horizontal concentration gradients. We further demonstrate a revised interpretation of vertical profile layer heights that improves agreement with aircraft profiles. These results support the use of Pandora HCHO observations for model evaluation and tropospheric chemistry applications.

Pandora formaldehyde (HCHO) retrievals in the boundary layer provide continuous observations of HCHO vertical distribution, yet validation of these retrievals remains limited. This work evaluates Pandora retrievals of the vertical distribution of formaldehyde (HCHO) against aircraft in situ measurements collected at four U.S. East Coast sites during the summers of 2024 and 2025. Tropospheric columns and vertical profiles are consistent with aircraft-based observations within measurement uncertainty, with agreement that depends critically on the alignment between the Pandora viewing geometry and local horizontal concentration gradients. We further demonstrate a revised interpretation of vertical profile layer heights that improves agreement with aircraft profiles. These results support the use of Pandora HCHO observations for model evaluation and tropospheric chemistry applications.

Pandora formaldehyde (HCHO) retrievals in the boundary layer provide continuous observations of HCHO vertical distribution, yet validation of these retrievals remains limited. This work evaluates Pandora retrievals of the vertical distribution of formaldehyde (HCHO) against aircraft in situ measurements collected at four U.S. East Coast sites during the summers of 2024 and 2025. Tropospheric columns and vertical profiles are consistent with aircraft-based observations within measurement uncertainty, with agreement that depends critically on the alignment between the Pandora viewing geometry and local horizontal concentration gradients. We further demonstrate a revised interpretation of vertical profile layer heights that improves agreement with aircraft profiles. These results support the use of Pandora HCHO observations for model evaluation and tropospheric chemistry applications.

Pandora formaldehyde (HCHO) retrievals in the boundary layer provide continuous observations of HCHO vertical distribution, yet validation of these retrievals remains limited. This work evaluates Pandora retrievals of the vertical distribution of formaldehyde (HCHO) against aircraft in situ measurements collected at four U.S. East Coast sites during the summers of 2024 and 2025. Tropospheric columns and vertical profiles are consistent with aircraft-based observations within measurement uncertainty, with agreement that depends critically on the alignment between the Pandora viewing geometry and local horizontal concentration gradients. We further demonstrate a revised interpretation of vertical profile layer heights that improves agreement with aircraft profiles. These results support the use of Pandora HCHO observations for model evaluation and tropospheric chemistry applications.

In recent years, significant perturbations to stratospheric inorganic chlorine have been observed following wildfires or volcanic eruptions, as well as modeled in simulations with elevated water vapor from overshooting convection or organic species in biomass burning aerosol. A detailed evaluation of inorganic chlorine in the stratosphere sampled under various conditions is presented here using high precision in situ aircraft measurements of chlorine monoxide (ClO) and chlorine nitrate (ClONO₂). Data were obtained over North America during the NASA Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) mission. The vertical distributions of ClO and ClONO₂ from all 29 research flights of the 2-year mission are found to be relatively compact and lacking substantial outliers. The peak mixing ratios are approximately 30 ppt and 400 ppt for ClO and ClONO₂, respectively. No chlorine activation was observed in the lower stratosphere in the presence of low temperatures and elevated water vapor from convective injection. Steady-state calculated ClONO₂ is found to be in good agreement with measured values, suggesting that a reduction in the uncertainty of the recommended rate coefficient for ClONO₂ production is possible. HCl is calculated at high time resolution throughout the mission using satellite data, and the resulting evaluation of the inorganic chlorine budget shows excellent agreement, with the ratio of ClO + ClONO₂ + HCl to total inorganic chlorine equal to 0.95 for mixing ratios greater than 500 ppt. No evidence of inorganic chlorine activation was observed during DCOTSS when aerosol organic mass fraction and biomass burning fraction were elevated.

Pandora formaldehyde (HCHO) retrievals in the boundary layer provide continuous observations of HCHO vertical distribution, yet validation of these retrievals remains limited. This work evaluates Pandora retrievals of the vertical distribution of formaldehyde (HCHO) against aircraft in situ measurements collected at four U.S. East Coast sites during the summers of 2024 and 2025. Tropospheric columns and vertical profiles are consistent with aircraft-based observations within measurement uncertainty, with agreement that depends critically on the alignment between the Pandora viewing geometry and local horizontal concentration gradients. We further demonstrate a revised interpretation of vertical profile layer heights that improves agreement with aircraft profiles. These results support the use of Pandora HCHO observations for model evaluation and tropospheric chemistry applications.