Atmospheric Chemistry Experiment Mission Research Articles

Pyrocumulonimbus Stratospheric Plume Injections Measured by the ACE‐FTS

AbstractThe Atmospheric Chemistry Experiment (ACE) is a satellite‐based mission that probes Earth's atmosphere via solar occultation. The primary instrument on board is a high‐resolution infrared Fourier transform spectrometer (Atmospheric Chemistry Experiment Fourier Transform Spectrometer, ACE‐FTS), providing altitude‐resolved volume mixing ratio measurements for numerous atmospheric constituents, including many biomass burning products. The ACE mission has observed the aftermath of three major pyrocumulonimbus events, in which extreme heat from intense fires created a pathway for directly injecting into the stratosphere plumes of gaseous and aerosol pollutants. These three events were associated with severe Australian bushfires from 2009 and 2019/2020, along with intense North American wildfires from summer 2017. The ACE‐FTS measured stratospheric plumes containing aerosols, enhanced levels of gaseous fire products, and tropospheric air transported into the stratosphere. Infrared spectral features indicate strikingly similar aerosol composition for all three events, characteristic of oxygenated organic matter.

Retrieval of carbon dioxide vertical profiles from solar occultation observations and associated error budgets for ACE-FTS and CASS-FTS

Abstract. An algorithm is developed to retrieve the vertical profile of carbon dioxide in the 5 to 25 km altitude range using mid-infrared solar occultation spectra from the main instrument of the ACE (Atmospheric Chemistry Experiment) mission, namely the Fourier transform spectrometer (FTS). The main challenge is to find an atmospheric phenomenon which can be used for accurate tangent height determination in the lower atmosphere, where the tangent heights (THs) calculated from geometric and timing information are not of sufficient accuracy. Error budgets for the retrieval of CO2 from ACE-FTS and the FTS on a potential follow-on mission named CASS (Chemical and Aerosol Sounding Satellite) are calculated and contrasted. Retrieved THs have typical biases of 60 m relative to those retrieved using the ACE version 3.x software after revisiting the temperature dependence of the N2 CIA (collision-induced absorption) laboratory measurements and accounting for sulfate aerosol extinction. After correcting for the known residual high bias of ACE version 3.x THs expected from CO2 spectroscopic/isotopic inconsistencies, the remaining bias for tangent heights determined with the N2 CIA is −20 m. CO2 in the 5–13 km range in the 2009–2011 time frame is validated against aircraft measurements from CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container), CONTRAIL (Comprehensive Observation Network for Trace gases by Airline), and HIPPO (HIAPER Pole-to-Pole Observations), yielding typical biases of −1.7 ppm in the 5–13 km range. The standard error of these biases in this vertical range is 0.4 ppm. The multi-year ACE-FTS data set is valuable in determining the seasonal variation of the latitudinal gradient which arises from the strong seasonal cycle in the Northern Hemisphere troposphere. The annual growth of CO2 in this time frame is determined to be 2.6 ± 0.4 ppm year−1, in agreement with the currently accepted global growth rate based on ground-based measurements.

ACE-FTS version 3.0 data set: validation and data processing update

On 12 August 2003, the Canadian-led Atmospheric Chemistry Experiment (ACE) was launched into a 74° inclination orbit at 650 km with the mission objective to measure atmospheric composition using infrared and UV-visible spectroscopy (Bernath et al. 2005). The ACE mission consists of two main instruments, ACE-FTS and MAESTRO (McElroy et al. 2007), which are being used to investigate the chemistry and dynamics of the Earth’s atmosphere. Here, we focus on the high resolution (0.02 cm-1) infrared Fourier Transform Spectrometer, ACE-FTS, that measures in the 750-4400 cm-1 (2.2 to 13.3 µm) spectral region. This instrument has been making regular solar occultation observations for more than nine years. The current ACE-FTS data version (version 3.0) provides profiles of temperature and volume mixing ratios (VMRs) of more than 30 atmospheric trace gas species, as well as 20 subsidiary isotopologues of the most abundant trace atmospheric constituents over a latitude range of ~85°N to ~85°S. This letter describes the current data version and recent validation comparisons and provides a description of our planned updates for the ACE-FTS data set. [...]

Laboratory procedure for simulating nadir measurements with the ACE-FTS

The Atmospheric Chemistry Experiment (ACE), or SCISAT mission, is a Canadian science satellite designed to investigate the chemical and dynamical processes that control the distribution of ozone in the stratosphere and upper troposphere. The ACE mission payload consists of two science instruments: a high-resolution infrared Fourier-Transform Spectrometer (FTS) and an ultraviolet/visible/near-infrared spectrometer. These instruments primarily function in occultation mode. However, during the dark portion of the orbit, the Earth passes between the Sun and the satellite. In this configuration, the ACE-FTS has the opportunity to acquire some nadir-view spectra of the Earth. Since the ACE-FTS was designed to view a hot source (i.e., the Sun) at high resolution using a single scan, it was necessary to determine if the ACE-FTS could also provide nadir spectra of the relatively cold atmosphere and surface with sufficient signal-to-noise ratio (SNR). As part of the pre-launch test program, laboratory measurements were performed to investigate this possibility. This paper reports the laboratory spectra of methane, ozone, and carbon monoxide gases measured with the ACE-FTS to determine the performance characteristics of the instrument when viewing a low-intensity blackbody source. From these results, it was shown that the ACE-FTS may be capable of measuring the column amounts of several abundant trace gases, such as methane, ozone, and nitrous oxide, in the atmosphere with sufficient SNR.

Aerosol extinction profiles at 525 nm and 1020 nm derived from ACE imager data: comparisons with GOMOS, SAGE II, SAGE III, POAM III, and OSIRIS

Abstract. The Canadian ACE (Atmospheric Chemistry Experiment) mission is dedicated to the retrieval of a large number of atmospheric trace gas species using the solar occultation technique in the infrared and UV/visible spectral domain. However, two additional solar disk imagers (at 525 nm and 1020 nm) were added for a number of reasons, including the retrieval of aerosol and cloud products. In this paper, we present first comparison results for these imager aerosol/cloud optical extinction coefficient profiles, with the ones derived from measurements performed by 3 solar occultation instruments (SAGE II, SAGE III, POAM III), one stellar occultation instrument (GOMOS) and one limb sounder (OSIRIS). The results indicate that the ACE imager profiles are of good quality in the upper troposphere/lower stratosphere, although the aerosol extinction for the visible channel at 525 nm contains a significant negative bias at higher altitudes, while the relative differences indicate that ACE profiles are almost always too high at 1020 nm. Both problems are probably related to ACE imager instrumental issues.

Atmospheric chemistry experiment (ACE): Analytical chemistry from orbit

ACE is a Canadian-led satellite mission that is measuring the concentrations of more than 30 atmospheric constituents by absorption spectroscopy using the Sun as a light source. The principal goal of the ACE mission is to make measurements that will improve understanding of the chemical and dynamic processes that control the distribution of ozone in the upper troposphere and stratosphere. The ACE instruments are an infrared Fourier transform spectrometer (FTS), a UV/visible/near IR spectrograph and a two-channel solar imager, all working in solar occultation mode. The high-resolution (0.02 cm −1) FTS is the primary instrument on the satellite, and it covers the mid-infrared spectral region (750–4400 cm −1).