Caroline R. Nowlan

Atmospheric Chemistry Experiment (ACE): Mission overview

SCISAT-1, also known as the Atmospheric Chemistry Experiment (ACE), is a Canadian satellite mission for remote sensing of the Earths atmosphere. It was launched into low Earth circular orbit (altitude 650 km, inclination 74°) on 12 Aug. 2003. The primary ACE instrument is a high spectral resolution (0.02 cm-1) Fourier Transform Spectrometer (FTS) operating from 2.2 to 13.3 μm (750-4400 cm-1). The satellite also features a dual spectrophotometer known as MAESTRO with wavelength coverage of 285-1030 nm and spectral resolution of 1-2 nm. A pair of filtered CMOS detector arrays records images of the Sun at 0.525 and 1.02 μm. Working primarily in solar occultation, the satellite provides altitude profile information (typically 10-100 km) for temperature, pressure, and the volume mixing ratios for several dozen molecules of atmospheric interest, as well as atmospheric extinction profiles over the latitudes 85°N to 85°S. This paper presents a mission overview and some of the first scientific results. Copyright 2005 by the American Geophysical Union.

The ACE-MAESTRO instrument on SCISAT: description, performance, and preliminary results

The Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (MAESTRO) instrument on the SCISAT satellite is a simple, compact spectrophotometer for the measurement of atmospheric extinction, ozone, nitrogen dioxide, and other trace gases in the stratosphere and upper troposphere as part of the Atmospheric Chemistry Experiment (ACE) mission. We provide an overview of the instrument from requirements to realization, including optical design, prelaunch and on-orbit performance, and a preliminary examination of retrievals of ozone and NO(2).

Global dry deposition of nitrogen dioxide and sulfur dioxide inferred from space‐based measurements

A method is developed to estimate global NO2 and SO2 dry deposition fluxes at high spatial resolution (0.1°×0.1°) using satellite measurements from the Ozone Monitoring Instrument (OMI) on the Aura satellite, in combination with simulations from the Goddard Earth Observing System chemical transport model (GEOS-Chem). These global maps for 2005–2007 provide a data set for use in examining global and regional budgets of deposition. In order to properly assess SO2 on a global scale, a method is developed to account for the geospatial character of background offsets in retrieved satellite columns. Globally, annual dry deposition to land estimated from OMI as NO2 contributes 1.5 ± 0.5 Tg of nitrogen and as SO2 contributes 13.7 ± 4.0 Tg of sulfur. Differences between OMI-inferred NO2 dry deposition fluxes and those of other models and observations vary from excellent agreement to an order of magnitude difference, with OMI typically on the low end of estimates. SO2 dry deposition fluxes compare well with in situ Clear Air Status and Trends Network-inferred flux over North America (slope = 0.98, r = 0.71). The most significant NO2 dry deposition flux to land per area occurs in the Pearl River Delta, China, at 13.9 kg N ha−1 yr−1, while SO2 dry deposition has a global maximum rate of 72.0 kg S ha−1 yr−1 to the east of Jinan in Chinas Shandong province. Dry deposition fluxes are explored in several urban areas, where NO2 contributes on average 9–36% and as much as 85% of total NOy dry deposition.

Initial comparison of ozone and NO2 profiles from ACE‐MAESTRO with balloon and satellite data

[1] Atmospheric retrievals of ozone and NO 2 by the Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (MAESTRO) instrument which is part of the Atmospheric Chemistry Experiment (ACE) satellite aboard SCISAT are compared statistically with coincident measurements by ozonesondes, the Fourier Transform Spectrometer (ACE-FTS) also aboard SCISAT, the SAGE III and the POAM III instruments. The ozone mixing ratio profiles from MAESTRO and ozonesondes agree within about 5-10% from 16-30 km in the northern middle and high latitudes. Further, ACE-FTS and MAESTRO ozone profiles agree within ∼5-15% from 16-50 km. MAESTRO ozone profiles show a systematic bias which is opposite for sunrise (SR) and sunset (SS) events and was also seen in comparisons with SAGE III and POAM III ozone. MAESTRO SS ozone profiles mostly agree within 5-10% from 16-40 km with either SAGE III or POAM III SR or SS retrievals, but show a significant high bias from 40-55 km, reaching a maximum of ∼20-30%. MAESTRO SR ozone profiles show a low bias of ∼5-15% from 20-50 km, as compared to SAGE III and POAM III SR or SS measurements. The NO 2 profiles agree within about 10-15% between ACE-FTS and MAESTRO from 15-40 km for the SR and 22-35 km for the SS measurements. Further, MAESTRO NO 2 profiles agree with SAGE III NO 2 mostly within 10% from 25-40 km. MAESTRO NO 2 profiles agree with POAM III SR profiles within 5-10% from 25-42 km. However, compared to POAM III SS profiles, MAESTRO NO 2 profiles show a low bias between 20 and 25 km (∼30-50%), a high MAESTRO bias between 25 and 32 km (10-30%), and again a low bias above 33 km that increases with altitude to 50-60%.

Characterization of the OCO-2 instrument line shape functions using on-orbit solar measurements

Accurately characterizing the instrument line shape (ILS) of the Orbiting Carbon Observatory-2 (OCO-2) is challenging and highly important due to its high spectral resolution and requirement for retrieval accuracy (0.25%) compared to previous spaceborne grating spectrometers. Onorbit ILS functions for all three bands of the OCO-2 instrument have been derived using its frequent solar measurements and high-resolution solar reference spectra. The solar reference spectrum generated from the 2016 version of the Total Carbon Column Observing Network (TCCON) solar line list shows significant improvements in the fitting residual compared to the solar reference spectrum currently used in the version 7 Level 2 algorithm in the O2 A band. The analytical functions used to represent the ILS of previous grating spectrometers are found to be inadequate for the OCO-2 ILS. Particularly, the hybrid Gaussian and super-Gaussian functions may introduce spurious variations, up to 5% of the ILS width, depending on the spectral sampling position, when there is a spectral undersampling. Fitting a homogeneous stretch of the preflight ILS together with the relative widening of the wings of the ILS is insensitive to the sampling grid position and accurately captures the variation of ILS in the O2 A band between decontamination events. These temporal changes of ILS may explain the spurious signals observed in the solar-induced fluorescence retrieval in barren areas.

The GeoTASO airborne spectrometer project

The NASA ESTO-funded Geostationary Trace gas and Aerosol Sensor Optimization (GeoTASO) development project demonstrates a reconfigurable multi-order airborne spectrometer and tests the performance of spectra separation and filtering on the sensor spectral measurements and subsequent trace gas and aerosol retrievals. The activities support mission risk reduction for the UV-Visible air quality measurements from geostationary orbit for the TEMPO and GEMS missions1 . The project helps advance the retrieval algorithm readiness through retrieval performance tests using scene data taken with varying sensor parameters. We report initial results of the project.

First Top‐Down Estimates of Anthropogenic NOx Emissions Using High‐Resolution Airborne Remote Sensing Observations

A number of satellite‐based instruments have become an essential part of monitoring emissions. Despite sound theoretical inversion techniques, the insufficient samples and the footprint size of current observations have introduced an obstacle to narrow the inversion window for regional models. These key limitations can be partially resolved by a set of modest high‐quality measurements from airborne remote sensing. This study illustrates the feasibility of nitrogen dioxide (NO_2) columns from the Geostationary Coastal and Air Pollution Events Airborne Simulator (GCAS) to constrain anthropogenic NO_x emissions in the Houston‐Galveston‐Brazoria area. We convert slant column densities to vertical columns using a radiative transfer model with (i) NO_2 profiles from a high‐resolution regional model (1 × 1 km^2) constrained by P‐3B aircraft measurements, (ii) the consideration of aerosol optical thickness impacts on radiance at NO_2 absorption line, and (iii) high‐resolution surface albedo constrained by ground‐based spectrometers. We characterize errors in the GCAS NO_2 columns by comparing them to Pandora measurements and find a striking correlation (r > 0.74) with an uncertainty of 3.5 × 10^(15) molecules cm^(−2). On 9 of 10 total days, the constrained anthropogenic emissions by a Kalman filter yield an overall 2–50% reduction in polluted areas, partly counterbalancing the well‐documented positive bias of the model. The inversion, however, boosts emissions by 94% in the same areas on a day when an unprecedented local emissions event potentially occurred, significantly mitigating the bias of the model. The capability of GCAS at detecting such an event ensures the significance of forthcoming geostationary satellites for timely estimates of top‐down emissions.

Ground-Based Measurements of Ozone and NO2 at Vanscoy, SK During the MANTRA 2000 and 2002 campaigns

We have deployed a UV-visible zenith-sky spectrometer in seven field campaigns to investigate Arctic and mid-latitude ozone depletion. In this presentation, we describe the instrument and present ozone and NO2 measurements obtained during MANTRA 2000 and 2002 campaigns.

Measurements of Stratospheric Trace Gases Column Density and J-values Using UV-Visible Photodiode Array Spectroscopy during the MANTRA 2002 Balloon Campaign

Three spectrophotometers were used to measure stratospheric constituents during the MANTRA2002 balloon campaign. The instrument, calibration, and observations are described. The raw data are now being analyzed, and the results will be compared with previous balloon flights.

First Results from a MAESTRO Instrument: Field-Testing MAESTRO-B During the MANTRA 2002 Balloon Campaign

The first atmospheric spectra recorded by a MAESTRO instrument were collected during the MANTRA 2002 field campaign. These spectra will be used in the development and testing of retrieval algorithms for the MAESTRO satellite instrument.