NO and NO2 act as catalysts for the oxidation of volatile organic compounds and lead to the formation of tropospheric ozone. ACE-FTS detects many of the organic source gases – a number of these for the first time – as well as the nitrogen oxide catalysts and the resulting ozone pollution in the upper troposphere. For example, the C1 series of oxygenated molecules, CH3OH (methanol, Dufour et al., 2006, 2007), CH2O (formaldehyde, Dufour et al., 2009) and HCOOH (formic acid, Abad et al., 2009), has been measured at elevated concentrations in biomass burning plumes and at background levels. Methanol is the second most abundant organic molecule in the atmosphere after methane and ACE was able to determine the first global distribution. The most recent new ACE organics are peroxyacetyl nitrate (PAN, Pope et al., 2016) and acetone (Dufour et al. 2016). ACE also contributed to the discovery of increasing amounts of ethane in the atmosphere (Franco et al., 2015) attributed to fugitive emissions associated with increased natural gas production (“fracking”). Acetone and PAN became routine data products in ACE-FTS data version 4.0/4.1.
ACE organics have been compared with the predictions of a number of chemical transport models including GEOS-Chem (e.g., Abad et al., 2011), LMDz-INCA (Dufour et al., 2007), GEM-AQ (Lupu et al., 2009) and WACCM (Park et al., 2013). These chemical transport models can be used for “chemical weather forecasting” and ACE ozone, for example, has been compared with MACC (Monitoring Atmospheric Composition & Climate) reanalysis (Inness et al., 2013). Although observations and models are in general agreement, model improvements in terms of chemistry, dynamics and emissions inventories are clearly needed. ACE observations were compared with the UKCA chemistry model by Archibald et al. (2020) and with the CMAM30 model (Kolonjari et al., 2018).
Fire plumes are readily detected by the ACE-FTS through enhanced concentrations of a variety of species emitted by combustion or produced in secondary chemical reactions. HCN is particularly useful for identifying biomass burning plumes because, unlike CO, it is emitted almost entirely by biomass combustion (Tereszchuk et al., 2011; 2013). High concentrations in young plumes facilitate detection, and Coheur et al. (2007) were the first to measure ethene, propyne, formaldehyde, acetone and peroxyacetyl nitrate (PAN) from orbit. Rinsland et al. (2007) found that H2O2 is enhanced in biomass burning plumes and Allen et al. (2013) determined a global distribution of this important atmospheric oxidizing agent.
Boone et al. (2020) measured pyrocumulonimbus stratospheric plume injections of many organic molecules as well as infrared spectra of smoke from forest fires. Pumphrey et al. (2018) used enhanced HCN from ACE-FTS to study fires in Indonesia during the 2015-2016 El Niño event. CH3CN, which is also produced almost entirely by fires, is now a routine ACE data product.
Volcanic eruptions can result in the production of large volumes of sulfate aerosols that can be seen by ACE. ACE-Imager and ACE-MAESTRO extinction profiles over a period of 7 months provided detailed information on the evolution of the aerosol layers from the 2008 Kasatochi volcanic eruption (Sioris et al., 2010). SO2 is now a routine ACE data product.
Sulfur-containing gases from ACE found considerable application because they result in the formation of stratospheric sulfate aerosols. Rollins et al. (2017) used in situ aircraft measurements and ACE retrievals of SO2 to demonstrate that background levels in the tropical tropopause region result in surprisingly little stratospheric aerosol production. ACE retrievals of SO2 and OCS were compared to those of MIPAS by Höpfner et al. (2015) and Glatthor et al. (2017), respectively. ACE OCS also contributed to the trend analysis by Lejeune et al. (2017). Yousefi et al. (2019) used OCS isotopologues to demonstrate that the major source of background stratospheric aerosols is from the oxidation of OCS.
In recent work, Lee et al. (2025) studied the influence of the Australian bushfire on the upper tropospheric CO and hydrocarbon distribution in the South Pacific. Glatthor et al. (2025) used a number of ACE data products to compare the geographic and seasonal variations of upper-tropospheric pollutants observed by MIPAS. Wizenberg et al. (2024) measured and modelled the trends of seven tropospheric pollutants in the high Arctic and ACE data was compared to for C2H2, C2H6, CH3OH, HCOOH, H2CO, and PAN.