C. A. McLinden

Air quality over the Canadian oil sands : a first assessment using satellite observations

Results from the first assessment of air quality over the Canadian oil sands–one of the largest industrial undertakings in human history–using satellite remote sensing observations of two pollutants, nitrogen dioxide (NO2) and sulfur dioxide (SO2), are presented. High-resolution maps were created that revealed distinct enhancements in both species over an area (roughly 30 km × 50 km) of intensive surface mining at scales of a few kilometers. The magnitude of these enhancements, quantified in terms of total mass, are comparable to the largest seen in Canada from individual sources. The rate of increase in NO2between 2005 and 2010 was assessed at 10.4 ± 3.5%/year and resulted from increases both in local values as well as the spatial extent of the enhancement. This is broadly consistent with both surface-measurement trends and increases in annual bitumen production. An increase in SO2 was also found, but given larger uncertainties, it is not statistically significant.

Lifetimes and emissions of SO2 from point sources estimated from OMI

A new method to estimate sulfur dioxide (SO2) lifetimes and emissions from point sources using satellite measurements is described. The method is based on fitting satellite SO2 vertical column density to a three-dimensional parameterization as a function of the coordinates and wind speed. An effective lifetime (or, more accurately, decay time) and emission rate are then determined from the parameters of the fit. The method was applied to measurements from the Ozone Monitoring Instrument (OMI) processed with the new principal component analysis (PCA) algorithm in the vicinity of approximately 50 large U.S. near-point sources. The obtained results were then compared with available emission inventories. The correlation between estimated and reported emissions was about 0.91 with the estimated lifetimes between 4 and 12 h. It is demonstrated that individual sources with annual SO2 emissions as low as 30 kt yr−1 can produce a statistically significant signal in OMI data.

Changes of tracer distributions in the doubled CO2 climate

Changes in tracer distributions in the troposphere and stratosphere are calculated from a control and doubled CO2 climate simulation run with the Goddard Institute for Space Studies Global Climate Middle Atmosphere Model. Transport changes are assessed using seven on-line tracers. Results show that interhemispheric transport is reduced by 5% along with a reduction in the Hadley circulation. Tropical transport from the troposphere into the stratosphere increases by some 30% associated with an increase in the stratospheric subtropical residual circulation. The tropical pipe becomes significantly more leaky, and greater transport into the lowermost stratosphere in the subtropics appears to be occurring, possibly in conjunction with a poleward shift in wave energy convergences. An increase in the high-latitude lower stratosphere residual circulation reduces the stratospheric residence time of extratropical injections such as bomb 14C by 11%. Vertical mixing within the troposphere by convection increases, reducing low level concentrations of tracers. The Hadley cell change is affected by the latitudinal gradient of tropical warming. The high-latitude lower stratosphere residual circulation change depends on the latitudinal gradient of the extratropical warming. Increased penetrating convection to the upper troposphere and the intensified residual circulation in the tropical upper troposphere/lower stratosphere appear to be the most robust of these results, with a magnitude that depends upon the degree of tropical warming. The consequence of this circulation change is to increase trace gas concentrations in the stratosphere and to decrease them in the troposphere for those species that have tropospheric sources.

A Decade of Global Volcanic SO2 Emissions Measured from Space

The global flux of sulfur dioxide (SO2) emitted by passive volcanic degassing is a key parameter that constrains the fluxes of other volcanic gases (including carbon dioxide, CO2) and toxic trace metals (e.g., mercury). It is also a required input for atmospheric chemistry and climate models, since it impacts the tropospheric burden of sulfate aerosol, a major climate-forcing species. Despite its significance, an inventory of passive volcanic degassing is very difficult to produce, due largely to the patchy spatial and temporal coverage of ground-based SO2 measurements. We report here the first volcanic SO2 emissions inventory derived from global, coincident satellite measurements, made by the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite in 2005–2015. The OMI measurements permit estimation of SO2 emissions from over 90 volcanoes, including new constraints on fluxes from Indonesia, Papua New Guinea, the Aleutian Islands, the Kuril Islands and Kamchatka. On average over the past decade, the volcanic SO2 sources consistently detected from space have discharged a total of ~63 kt/day SO2 during passive degassing, or ~23 ± 2 Tg/yr. We find that ~30% of the sources show significant decadal trends in SO2 emissions, with positive trends observed at multiple volcanoes in some regions including Vanuatu, southern Japan, Peru and Chile.

Odin/OSIRIS observations of stratospheric BrO: Retrieval methodology, climatology, and inferred Bry

A 7+ year (2001–2008) data set of stratospheric BrO profiles measured by the Optical Spectrograph and Infra-Red Imager System (OSIRIS) instrument, a UV-visible spectrometer measuring limb-scattered sunlight from the Odin satellite, is presented. Zonal mean radiance spectra are computed for each day and inverted to yield effective daily zonal mean BrO profiles from 16 to 36 km. A detailed description of the retrieval methodology and error analysis is presented. Single-profile precision and effective resolution are found to be about 30% and 3–5 km, respectively, throughout much of the retrieval range. Individual profile and monthly mean comparisons with ground-based, balloon, and satellite instruments are found to agree to about 30%. A BrO climatology is presented, and its morphology and correlation with NO2 is consistent with our current understanding of bromine chemistry. Monthly mean Bry maps are derived. Two methods of calculating total Bry in the stratosphere are used and suggest (21.0 ± 5.0) pptv with a contribution from very short lived substances of (5.0 ± 5.0) pptv, consistent with other recent estimates.

A global inventory of stratospheric NOy from ACE-FTS

The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) on board the Canadian SCISAT-1 satellite (launched in August 2003) measures over 30 different atmospheric species, including six nitrogen trace gases that are needed to quantify the stratospheric NOy budget. We combine volume mixing ratio (VMR) profiles for NO, NO2, HNO3, N2O5, ClONO2, and HNO4 to determine a zonally averaged NOy climatology on monthly and 3 month combined means (December–February, March–May, June–August, and September–November) at 5° latitude spacing and on 33 pressure surfaces. Peak NOy VMR concentrations (15–20 ppbv) are situated at about 3 hPa (∼40 km) in the tropics, while they are typically lower at about 10 hPa (∼30 km) in the midlatitudes. Mean NOy VMRs are similar in both the northern and southern polar regions, with the exception of large enhancements periodically observed in the upper stratosphere and lower mesosphere. These are primarily due to enhancements of NO due to energetic particle precipitation and downward transport. Other features in the NOy budget are related to descent in the polar vortex, heterogeneous chemistry, and denitrification processes. Comparison of the ACE-FTS NOy budget is made to both the Odin and ATMOS NOy data sets, showing in both cases a good level of agreement, such that relative differences are typically better than 20%. The NOy climatological products are available through the ACE website and are a supplement to the paper. - A middle-atmosphere NOy climatology has been produced using ACE-FTS measurements; - A robust method for quality controlling the input data has been developed - Good agreement is found between ACE-FTS NOy climatology and other climatologies

Vertical profiles of lightning-produced NO 2 enhancements in the upper troposphere observed by OSIRIS

The purpose of this study is to perform a global search of the upper troposphere (z ≥10 km) for enhancements of nitrogen dioxide and determine their sources. This is the first application of satellite-based limb scattering to study upper tropospheric NO2. We have searched two years (May 2003–May 2005) of OSIRIS (Optical Spectrograph and Infrared Imager System) operational NO 2concentrations (version 2.3/2.4) to find large enhancements in the observations by comparing with photochemical box model calculations and by identifying local maxima in NO 2 volume mixing ratio. We find that lightning is the main production mechanism responsible for the large enhancements in OSIRIS NO 2 observations as expected. Similar patterns in the abundances and spatial distribution of the NO 2 enhancements are obtained by perturbing the lightning within the GEOS-Chem 3-dimensional chemical transport model. In most cases, the presence of lightning is confirmed with coincident imagery from LIS (Lightning Imaging Sensor) and the spatial extent of the NO2 enhancement is mapped using nadir observations of tropospheric NO 2 at high spatial resolution from SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography) and OMI (Ozone Monitoring Instrument). The combination of the lightning and chemical sensors allows us to investigate globally the role of lightning to the abundance of NO 2 in the upper troposphere (UT). Lightning contributes 60% of the tropical upper tropospheric NO2 in GEOS-Chem simulations. The spatial and temporal distribution of NO2 enhancements from lightning (May Correspondence to: C. E. Sioris (christopher.sioris@ec.gc.ca) 2003–May 2005) is investigated. The enhancements generally occur at 12 to 13 km more frequently than at 10 to 11 km. This is consistent with the notion that most of the NO 2 is forming and persisting near the cloud top altitude in the tropical upper troposphere. The latitudinal distribution is mostly as expected. In general, the thunderstorms exhibiting weaker vertical development (e.g. 11 ≤z≤13 km) extend latitudinally as far poleward as 45 ◦ but the thunderstorms with stronger vertical development (z ≥14 km) tend to be located within 33 of the equator. There is also the expected hemispheric asymmetry in the frequency of the NO 2 enhancements, as most were observed in the northern hemisphere for the period analyzed.

Quantifying stratospheric ozone trends: Complications due to stratospheric cooling

[1] Recent studies suggest that ozone turnaround (the second stage of ozone recovery) is near. Determining precisely when this occurs, however, will be complicated by greenhouse gas‐induced stratospheric cooling as ozone trends derived from profile data in different units and/or vertical co‐ordinates will not agree. Stratospheric cooling leads to simultaneous trends in air density and layer thicknesses, confounding the interpretation of ozone trends. A simple model suggests that instruments measuring ozone in different units may differ as to the onset of turnaround by a decade, with some indicting a continued decline while others an increase. This concept was illustrated by examining the long‐term (1979–2005) ozone trends in the SAGE (Stratospheric Aerosol and Gas Experiment) and SBUV (Solar Backscatter Ultraviolet) time series. Trends from SAGE, which measures number density as a function of altitude, and SBUV, which measures partial column as a function of pressure, are known to differ by 4–6%/decade in the upper stratosphere. It is shown that this long‐ standing difference can be reconciled to within 2%/decade when the trend in temperature is properly accounted for. Citation: McLinden, C. A., and V. Fioletov (2011), Quantifying stratospheric ozone trends: Complications due to stratospheric cooling, Geophys. Res. Lett., 38, L03808, doi:10.1029/2010GL046012.

A global ozone climatology from ozone soundings via trajectory mapping: a stratospheric perspective

This study explores a domain-filling trajectory approach to generate a global ozone climatology from relatively sparse ozonesonde data. Global ozone soundings comprising 51 898 profiles at 116 stations over 44 yr (1965–2008) are used, from which forward and backward trajectories are calculated from meteorological reanalysis data to map ozone measurements to other locations and so fill in the spatial domain. The resulting global ozone climatology is archived monthly for five decades from the 1960s to the 2000s on a grid of 5 × 5 × 1 km (latitude, longitude, and altitude), from the surface to 26 km altitude. It is also archived yearly for the same period. The climatology is validated at 20 selected ozonesonde stations by comparing the actual ozone sounding profile with that derived through trajectory mapping of ozone sounding data from all stations except the one being compared. The two sets of profiles are in good agreement, both overall with correlation coefficient r = 0.991 and root mean square (RMS) of 224 ppbv and individually with r from 0.975 to 0.998 and RMS from 87 to 482 ppbv. The ozone climatology is also compared with two sets of satellite data from the Satellite Aerosol and Gas Experiment (SAGE) and the Optical Spectrography and InfraRed Imager System (OSIRIS). The ozone climatology compares well with SAGE and OSIRIS data in both seasonal and zonal means. The mean differences are generally quite small, with maximum differences of 20 % above 15 km. The agreement is better in the Northern Hemisphere, where there are more ozonesonde stations, than in the Southern Hemisphere; it is also better in the middle and high latitudes than in the tropics where reanalysis winds are less accurate. This ozone climatology captures known features in the stratosphere as well as seasonal and decadal variations of these features. The climatology clearly shows the depletion of ozone from the 1970s to the mid 1990s and ozone increases in the 2000s in the lower stratosphere. When this climatology is used as the upper boundary condition in an Environment Canada operational chemical forecast model, the forecast is improved in the vicinity of the upper troposphere-lower stratosphere (UTLS) region. This ozone climatology is latitudinally, longitudinally, and vertically resolved and it offers more complete high latitude coverage as well as a much longer record than current satellite data. As the climatology depends on neither a priori data nor photochemical modeling, it provides independent information and insight that can supplement satellite data and model simulations of stratospheric ozone. Published by Copernicus Publications on behalf of the European Geosciences Union. 11442 J. Liu et al.: A global ozone climatology from ozone soundings: a stratospheric perspective

Stratospheric ozone during the Last Glacial Maximum

[1] Stratospheric ozone during the Last Glacial Maximum (LGM) is investigated in on-line simulations with the GISS Global Climate/Middle Atmosphere Model 3. LGM boundary conditions and atmospheric concentrations are employed in three simulations: without interactive ozone, with ozone photochemistry appropriate for that time period and with the LGM climate but current atmospheric composition for chemistry. Results show stratospheric ozone increased during the LGM due to reduced NOy and chlorine, while warmer stratospheric temperatures (from reduced stratospheric CO 2 ) decrease ozone with current photochemistry. The stratospheric residual circulation intensified in the lowermost stratosphere, increasing stratosphere/troposphere exchange at higher latitudes, although for most of the middle atmosphere the circulation decreased; the age of air in the Middle Atmosphere increased by up to one year. Compared with the vastly different LGM conditions, increase in stratospheric ozone of 2% by mass had little effect on atmospheric dynamics, and increased the global radiation balance by <0.1 Wm ―2 .