Atmospheric Chemistry Experiment Satellite Research Articles

Abundances of 15NO2 and H15NO3 in the stratosphere

Using ACE (Atmospheric Chemistry Experiment) satellite data, the volume mixing ratios (VMRs) of stratospheric NO2 and HNO3 and their 15N minor isotopologues have been determined, including global patterns and seasonal trends. Stratospheric δ15N values for NO2 and HNO3 have been calculated using VMR data. 14NO2 is relatively enhanced over the winter pole and over the equator in the lower stratosphere but at higher altitudes 15NO2 is enhanced over the winter pole. H15NO3 is relatively enhanced in the lower stratosphere over the summer pole but in the upper stratosphere H14NO3 is enhanced.

Atlas of ACE spectra of clouds and aerosols

Clouds and aerosols play a vital role in the Earth's climate. Detecting polar mesospheric clouds, polar stratospheric clouds and aerosols is useful for monitoring climate change and atmospheric chemistry. ACE (Atmospheric Chemistry Experiment) satellite data are used to provide an infrared spectral atlas of polar mesospheric clouds, three types of polar stratospheric clouds (nitric acid trihydrate, sulfuric/nitric acid ternary solutions, and ice), cirrus clouds, stratospheric smoke from fires and sulfate aerosols. Most of the example spectra have been modeled using the appropriate optical constants and the calculated extinction of sunlight by the particles.

Stratospheric and mesospheric H2O and CH4 trends from the ACE satellite mission

The Atmospheric Chemistry Experiment (ACE) Fourier transform spectrometer (FTS) has been measuring water vapor and methane in the stratosphere and mesosphere from low Earth orbit since 2004. Recently, substantial increases in water vapor in the upper atmosphere were observed with the MLS and SABER satellite instruments. The main source of water vapor in the upper atmosphere is methane oxidation. ACE-FTS data show substantial water and methane increases, and confirm that the methane increases are too small to explain the water increases. Therefore, changes in the transport of water across the tropical tropopause layer and in atmospheric dynamics are responsible for the positive water trends.

Trends in halogen-containing molecules measured by the Atmospheric Chemistry Experiment (ACE) satellite

The Montreal Protocol has banned the production of long-lived halogen-containing molecules such as chlorofluorocarbons (CFCs) that are responsible for the widespread destruction of stratospheric ozone. Sixteen halogen-containing trace gases (CCl4, CF4, CFC-11, CFC-12, CFC-113, CH3Cl, ClONO2, COCl2, COClF, COF2, HCFC-22, HCFC-141b, HCFC-142b, HCl, HF, SF6) are observed globally by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) which measures atmospheric spectra via solar occultation from low-Earth orbit. The ACE satellite was launched in August 2003 and continues to operate with minimal degradation to this day. ACE is uniquely able to provide global long term trends of the concentrations of many atmospheric constituents. In this work we present time series trends and altitude-latitude distributions of halogen-containing trace gases. For 12 molecules the altitude-latitude distributions are reliable, but for CF4, CFC-113, HCFC-141b and HCFC-142b the distributions are anomalous likely because of spectroscopic interference in the retrieval. These 16 species can be categorized as source gases such as CFCs emitted at the surface and product gases such as HCl, HF and ClONO2 that are formed by chemical reactions from the source gases. Many of these substances deplete stratospheric ozone and are potent greenhouse gases that contribute to climate change.

Properties of polar mesospheric clouds from ACE satellite infrared spectra

An analysis of the Atmospheric Chemistry Experiment (ACE) infrared Fourier transform spectrometer (FTS) spectra for signatures of Polar Mesospheric Clouds (PMCs) has been carried out by looking for the O-H vibrational mode at ≈ 3240 cm−1. PMCs are thought to be indicators of climate change in the mesosphere and have been found to be increasing in recent years. Additionally, there are a number of open questions about the microphysics of the clouds, and their physical properties such as temperature, density, and particle shape and size. ACE has access to the entire infrared spectrum, potentially providing more accurate retrievals of these parameters. Using the T-matrix scattering code, we have made fits to the 3 micron ACE-FTS spectra. The ACE data set yielded 1762 unique occultations; after accounting for false positives, 955 occultations were left. We assumed oblate spheroids with a fixed effective radius of 40 nm and a nominal cloud size of 200 km, and obtained reasonable distributions for temperature, axial ratio and particle density. We expect that the methods presented here will allow a new routine ACE PMC data product to be developed.

Validation of ACE and OSIRIS ozone and NO<sub>2</sub> measurements using ground-based instruments at 80° N

Abstract. The Optical Spectrograph and Infra-Red Imager System (OSIRIS) and the Atmospheric Chemistry Experiment (ACE) have been taking measurements from space since 2001 and 2003, respectively. This paper presents intercomparisons between ozone and NO2 measured by the ACE and OSIRIS satellite instruments and by ground-based instruments at the Polar Environment Atmospheric Research Laboratory (PEARL), which is located at Eureka, Canada (80° N, 86° W) and is operated by the Canadian Network for the Detection of Atmospheric Change (CANDAC). The ground-based instruments included in this study are four zenith-sky differential optical absorption spectroscopy (DOAS) instruments, one Bruker Fourier transform infrared spectrometer (FTIR) and four Brewer spectrophotometers. Ozone total columns measured by the DOAS instruments were retrieved using new Network for the Detection of Atmospheric Composition Change (NDACC) guidelines and agree to within 3.2%. The DOAS ozone columns agree with the Brewer spectrophotometers with mean relative differences that are smaller than 1.5%. This suggests that for these instruments the new NDACC data guidelines were successful in producing a homogenous and accurate ozone dataset at 80° N. Satellite 14–52 km ozone and 17–40 km NO2 partial columns within 500 km of PEARL were calculated for ACE-FTS Version 2.2 (v2.2) plus updates, ACE-FTS v3.0, ACE-MAESTRO (Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) v1.2 and OSIRIS SaskMART v5.0x ozone and Optimal Estimation v3.0 NO2 data products. The new ACE-FTS v3.0 and the validated ACE-FTS v2.2 partial columns are nearly identical, with mean relative differences of 0.0 ± 0.2% and −0.2 ± 0.1% for v2.2 minus v3.0 ozone and NO2, respectively. Ozone columns were constructed from 14–52 km satellite and 0–14 km ozonesonde partial columns and compared with the ground-based total column measurements. The satellite-plus-sonde measurements agree with the ground-based ozone total columns with mean relative differences of 0.1–7.3%. For NO2, partial columns from 17 km upward were scaled to noon using a photochemical model. Mean relative differences between OSIRIS, ACE-FTS and ground-based NO2 measurements do not exceed 20%. ACE-MAESTRO measures more NO2 than the other instruments, with mean relative differences of 25–52%. Seasonal variation in the differences between NO2 partial columns is observed, suggesting that there are systematic errors in the measurements and/or the photochemical model corrections. For ozone spring-time measurements, additional coincidence criteria based on stratospheric temperature and the location of the polar vortex were found to improve agreement between some of the instruments. For ACE-FTS v2.2 minus Bruker FTIR, the 2007–2009 spring-time mean relative difference improved from −5.0 ± 0.4% to −3.1 ± 0.8% with the dynamical selection criteria. This was the largest improvement, likely because both instruments measure direct sunlight and therefore have well-characterized lines-of-sight compared with scattered sunlight measurements. For NO2, the addition of a ±1° latitude coincidence criterion improved spring-time intercomparison results, likely due to the sharp latitudinal gradient of NO2 during polar sunrise. The differences between satellite and ground-based measurements do not show any obvious trends over the missions, indicating that both the ACE and OSIRIS instruments continue to perform well.

Simultaneous trace gas measurements using two Fourier transform spectrometers at Eureka, Canada during spring 2006, and comparisons with the ACE-FTS

Abstract. The 2006 Canadian Arctic ACE (Atmospheric Chemistry Experiment) Validation Campaign collected measurements at the Polar Environment Atmospheric Research Laboratory (PEARL, 86.42° W, 80.05° N, 610 m a.s.l.) at Eureka, Canada from 17 February to 31 March 2006. Two of the ten instruments involved in the campaign, both Fourier transform spectrometers (FTSs), were operated simultaneously, recording atmospheric solar absorption spectra. The first instrument was an ABB Bomem DA8 high-resolution infrared FTS. The second instrument was the Portable Atmospheric Research Interferometric Spectrometer for the Infrared (PARIS-IR), the ground-based version of the satellite-borne FTS on the ACE satellite (ACE-FTS). From the measurements collected by these two ground-based instruments, total column densities of seven stratospheric trace gases (O3, HCl, ClONO2, HF, HNO3, NO2, and NO) were retrieved using the optimal estimation method and these results were compared. Since the two instruments sampled the same portions of atmosphere by synchronizing observations during the campaign and used consistent retrieval parameters, the biases in retrieved columns from the two spectrometers represent the instrumental differences. Mean differences in total column densities of O3, HCl, ClONO2, HF, HNO3, and NO2 from the observations between PARIS-IR and the DA8 FTS are 2.8 %, −3.2 %, −4.3 %, −1.5 %, −1.9 %, and −0.1 %, respectively. Partial column results from the ground-based spectrometers were also compared with partial columns derived from ACE-FTS version 2.2 (including updates for O3) profiles. Mean differences in partial column densities of O3, HCl, ClONO2, HF, HNO3, NO2, and NO from the measurements between ACE-FTS and the DA8 FTS are −5.9 %, −8.5 %, −11.8 %, −0.9 %, −6.6 %, −21.6 % and −7.6 % respectively. Mean differences in partial column densities of O3, HCl, ClONO2, HF, HNO3, NO2 from the measurements between ACE-FTS and the PARIS-IR are −5.2 %, −4.6 %, −2.3 %, −4.7 %, 5.7 % and −11.9 %, respectively. This work provides further evidence of the reliability of ACE-FTS measurements from the first three years of on-orbit observations. Column densities of O3, HCl, ClONO2, and HNO3 from the three FTSs were normalized with respect to HF and used to compare the time evolution of the chemical constituents in the atmosphere over Eureka during spring 2006.

Intercomparison of UV-visible measurements of ozone and NO<sub>2</sub> during the Canadian Arctic ACE validation campaigns: 2004–2006

Abstract. The first three Canadian Arctic ACE validation campaigns were held during polar sunrise at Eureka, Nunavut, Canada (80° N, 86° W) from 2004 to 2006 in support of validation of the ACE (Atmospheric Chemistry Experiment) satellite mission. Three or four zenith-sky viewing UV-visible spectrometers have taken part in each of the three campaigns. The differential slant column densities and vertical column densities of ozone and NO2 from these instruments have been compared following the methods of the UV-visible Working Group of the NDACC (Network for Detection of Atmospheric Composition Change). The instruments are found to partially agree within the required accuracies for both species, although both the vertical and slant column densities are more scattered than required. This might be expected given the spatial and temporal variability of the Arctic stratosphere in spring. The vertical column densities are also compared to integrated total columns from ozonesondes and integrated partial columns from the ACE-FTS (ACE-Fourier Transform Spectrometer) and ACE-MAESTRO (ACE-Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) instruments on board ACE. For both species, the columns from the ground-based instruments and the ozonesondes are found to generally agree within their combined error bars. The ACE-FTS ozone partial columns and the ground-based total columns agree within 4.5%, averaged over the three campaigns. The ACE-MAESTRO ozone partial columns are generally smaller than those of the ground-based instruments, by an average of 9.9%, and are smaller than the ACE-FTS columns by an average of 14.4%. The ACE-FTS NO2 partial columns are an average of 13.4% smaller than the total columns from the ground-based instruments, as expected. The ACE-MAESTRO NO2 partial columns are larger than the total columns of the ground-based instruments by an average of 2.5% and are larger than the partial columns of the ACE-FTS by an average of 15.5%.