27 research outputs found
Simultaneous atmospheric measurements using two Fourier transform infrared spectrometers at the Polar Environment Atmospheric Research Laboratory during spring 2006, and comparisons with the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer
International audienceThe 2006 Canadian Arctic ACE (Atmospheric Chemistry Experiment) Validation Campaign collected measurements at the Polar Environment Atmospheric Research Laboratory (PEARL, 80.05° N, 86.42° W, 610 m above sea level) 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, HNO3, NO2, HCl, HF, NO, and ClONO2 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, the biases in retrieved columns from the two spectrometers represent the instrumental differences. These differences were consistent with those seen in previous FTS intercomparison studies. 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, HDO and N2O5 profiles and the differences found were consistent with the other validation comparison studies for the ACE-FTS version 2.2 data products. Column densities of O3, HCl, ClONO2, and HNO3 from the three FTSs were normalized with respect to HF and used to probe the time evolution of the chemical constituents in the atmosphere over Eureka during spring 2006
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Assessing stratospheric transport in the CMAM30 simulations using ACE-FTS measurements
Stratospheric transport in global circulation models and chemistry–climate models is an important component in simulating the recovery of the ozone layer as well as changes in the climate system. The Brewer–Dobson circulation is not well constrained by observations and further investigation is required to resolve uncertainties related to the mechanisms driving the circulation. This study has assessed the specified dynamics mode of the Canadian Middle Atmosphere Model (CMAM30) by comparing to the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) profile measurements of CFC-11 (CCl3F), CFC-12 (CCl2F2), and N2O. In the CMAM30 specified dynamics simulation, the meteorological fields are nudged using the ERA-Interim reanalysis and a specified tracer was employed for each species, with hemispherically defined surface measurements used as the boundary condition. A comprehensive sampling technique along the line of sight of the ACE-FTS measurements has been utilized to allow for direct comparisons between the simulated and measured tracer concentrations. The model consistently overpredicts tracer concentrations of CFC-11, CFC-12, and N2O in the lower stratosphere, particularly in the northern hemispheric winter and spring seasons. The three mixing barriers investigated, including the polar vortex, the extratropical tropopause, and the tropical pipe, show that there are significant inconsistencies between the measurements and the simulations. In particular, the CMAM30 simulation underpredicts mixing efficiency in the tropical lower stratosphere during the June–July–August season
MIPAS IMK/IAA CFC-11 (CCl₃F) and CFC-12 (CCl₂F₂) measurements: accuracy, precision and long-term stability
Profiles of CFC-11 (CCl3F) and CFC-12 (CCl2F2) of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) abord the European satellite Envisat have been retrieved from versions MIPAS/4.61–MIPAS/4.62 and MIPAS/5.02–MIPAS/5.06 level-1b data using the scientific level-2 processor run by Karlsruhe Institute of Technology (KIT), Institute of Meteorology and Climate Research (IMK) and Consejo Superior de Investigaciones CientÃficas (CSIC), Instituto de AstrofÃsica de AndalucÃa (IAA). These profiles have been compared to measurements taken by the balloon borne Cryosampler, Mark IV (MkIV) and MIPAS-Balloon (MIPAS-B), the airborne MIPAS stratospheric aircraft (MIPAS-STR), the satellite borne Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) and the High Resolution Dynamic Limb Sounder (HIRDLS) as well as the ground based Halocarbon and other Atmospheric Trace Species (HATS) network for the reduced spectral resolution period (RR: January 2005–April 2012) of MIPAS Envisat. ACE-FTS, MkIV and HATS also provide measurements during the high spectral resolution period (FR: July 2002–March 2004) and were used to validate MIPAS Envisat CFC-11 and CFC-12 products during that time, as well as ILAS-II profiles. In general, we find that MIPAS Envisat shows slightly higher values for CFC-11 at the lower end of the profiles (below ~ 15 km) and in a comparison of HATS ground-based data and MIPAS Envisat measurements at 3 km below the tropopause. Differences range from approximately 10–50 pptv (~ 5–20 %) during the RR period. In general, differences are slightly smaller for the FR period. An indication of a slight high-bias at the lower end of the profile exists for CFC-12 as well, but this bias is far less pronounced than for CFC-11, so that differences at the lower end of the profile (below ~ 15 km) and in the comparison of HATS and MIPAS Envisat measurements taken at 3 km below the tropopause mainly stay within 10–50 pptv (~ 2–10 %) for the RR and the FR period. Above approximately 15 km, most comparisons are close to excellent, apart from ILAS-II, which shows large differences above ~ 17 km. Overall, percentage differences are usually smaller for CFC-12 than for CFC-11. For both species – CFC-11 and CFC-12 – we find that differences at the lower end of the profile tend to be larger at higher latitudes than in tropical and subtropical regions. In addition, MIPAS Envisat profiles have a maximum in the mixing ratio around the tropopause, which is most obvious in tropical mean profiles. Estimated measurement noise alone can, in most cases, not explain the standard deviation of the differences. This is attributed to error components not considered in the error estimate and also to natural variability which always plays a role when the compared instruments do not measure exactly the same air mass. Investigations concerning the temporal stability show very small negative drifts in MIPAS Envisat CFC-11 measurements. These drifts vary between ~ 1–3 % decade−1. For CFC-12, the drifts are also negative and close to zero up to ~ 30 km. Above that altitude larger drifts of up to ~ 50 % decade−1 appear which are negative up to ~ 35 km and positive, but of a similar magnitude, above
Validation of ACE and OSIRIS ozone and NO2 measurements using ground-based instruments at 80 degrees N
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 (80A degrees N, 86A degrees 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 80A degrees 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 +/- 1A degrees 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
Characterization of aerosol growth events over Ellesmere Island during the summers of 2015 and 2016
The occurrence of frequent aerosol nucleation and growth events in the Arctic
during summertime may impact the region's climate through increasing the
number of cloud condensation nuclei in the Arctic atmosphere. Measurements of
aerosol size distributions and aerosol composition were taken during the
summers of 2015 and 2016 at Eureka and Alert on Ellesmere Island in Nunavut,
Canada. These results provide a better understanding of the frequency and
spatial extent of elevated Aitken mode aerosol concentrations as well as of
the composition and sources of aerosol mass during particle growth. Frequent
appearances of small particles followed by growth occurred throughout the
summer. These particle growth events were observed beginning in June with the
melting of the sea ice rather than with the polar sunrise, which strongly
suggests that influence from the marine boundary layer was the primary cause
of the events. Correlated particle growth events at the two sites, separated
by 480 km, indicate conditions existing over large scales play a key role in
determining the timing and the characteristics of the events.
In addition, aerosol mass spectrometry measurements were used to analyze the
size-resolved chemical composition of aerosols during two selected growth
events. It was found that particles with diameters between 50 and 80 nm
(physical diameter) during these growth events were predominately organic
with only a small sulfate contribution. The oxidation of the organics also
changed with particle size, with the fraction of organic acids increasing
with diameter from 80 to 400 nm.
The growth events at Eureka were observed most often when the temperature
inversion between the sea and the measurement site (at 610 m a.s.l.) was
non-existent or weak, presumably creating conditions with low aerosol
condensation sink and allowing fresh marine emissions to be mixed upward to
the observatory's altitude. While the nature of the gaseous precursors
responsible for the growth events is still poorly understood, oxidation of
dimethyl sulfide alone to produce particle-phase sulfate or
methanesulfonic acid was inconsistent with the measured aerosol composition,
suggesting the importance of other gas-phase organic compounds condensing for
particle growth.</p
MIPAS IMK/IAA CFC-11 (CCl<sub>3</sub>F) and CFC-12 (CCl<sub>2</sub>F<sub>2</sub>) measurements: accuracy, precision and long-term stability
MIPAS IMK/IAA CFC-11 (CCl₃F) and CFC-12 (CCl₂F₂) measurements: Accuracy, precision and long-term stability
Profiles of CFC-11 (CClF) and CFC-12 (CClF) of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) aboard the European satellite Envisat have been retrieved from versions MIPAS/4.61 to MIPAS/ 4.62 and MIPAS/5.02 to MIPAS/5.06 level-1b data using the scientific level-2 processor run by Karlsruhe Institute of Technology (KIT), Institute of Meteorology and Climate Research (IMK) and Consejo Superior de Investigaciones CientÃficas (CSIC), Instituto de AstrofÃsica de AndalucÃa (IAA). These profiles have been compared to measurements taken by the balloon-borne cryosampler, Mark IV (MkIV) and MIPAS-Balloon (MIPAS-B), the airborne MIPAS-STRatospheric aircraft (MIPAS-STR), the satellite-borne Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) and the High Resolution Dynamic Limb Sounder (HIRDLS), as well as the groundbased Halocarbon and other Atmospheric Trace Species (HATS) network for the reduced spectral resolution period (RR: January 2005–April 2012) of MIPAS. ACE-FTS, MkIV and HATS also provide measurements during the high spectral resolution period (full resolution, FR: July 2002–March 2004) and were used to validate MIPAS CFC-11 and CFC- 12 products during that time, as well as profiles from the Improved Limb Atmospheric Spectrometer, ILAS-II. In general, we find that MIPAS shows slightly higher values for CFC-11 at the lower end of the profiles (below 15 km) and in a comparison of HATS ground-based data and MIPAS measurements at 3 km below the tropopause. Differences range from approximately 10 to 50 pptv ( ~5–20 %) during the RR period. In general, differences are slightly smaller for the FR period. An indication of a slight high bias at the lower end of the profile exists for CFC-12 as well, but this bias is far less pronounced than for CFC-11 and is not as obvious in the relative differences between MIPAS and any of the comparison instruments. Differences at the lower end of the profile (below ~15 km) and in the comparison of HATS and MIPAS measurements taken at 3 km below the tropopause mainly stay within 10–50 pptv (corresponding to ~ 2–10% for CFC-12) for the RR and the FR period. Between ~15 and 30 km, most comparisons agree within 10–20 pptv (10–20 %), apart from ILAS-II, which shows large differences above ~17 km. Overall, relative differences are usually smaller for CFC-12 than for CFC-11. For both species – CFC-11 and CFC-12 – we find that differences at the lower end of the profile tend to be larger at higher latitudes than in tropical and subtropical regions. In addition, MIPAS profiles have a maximum in their mixing ratio around the tropopause, which is most obvious in tropical mean profiles. Comparisons of the standard deviation in a quiescent atmosphere (polar summer) show that only the CFC-12 FR error budget can fully explain the observed variability, while for the other products (CFC-11 FR and RR and CFC-12 RR) only two-thirds to three-quarters can be explained. Investigations regarding the temporal stability show very small negative drifts in MIPAS CFC-11 measurements. These instrument drifts vary between ~1 and 3% decade. For CFC-12, the drifts are also negative and close to zero up to ~30 km. Above that altitude, larger drifts of up to 50% decade appear which are negative up to ~35 km and positive, but of a similar magnitude, above
Overview paper: New insights into aerosol and climate in the Arctic
Motivated by the need to predict how the Arctic atmosphere will
change in a warming world, this article summarizes recent advances made by
the research consortium NETCARE (Network on Climate and Aerosols: Addressing
Key Uncertainties in Remote Canadian Environments) that contribute to our
fundamental understanding of Arctic aerosol particles as they relate to
climate forcing. The overall goal of NETCARE research has been to use an
interdisciplinary approach encompassing extensive field observations and a
range of chemical transport, earth system, and biogeochemical models. Several
major findings and advances have emerged from NETCARE since its formation in
2013. (1)Â Unexpectedly high summertime dimethyl sulfide (DMS) levels were
identified in ocean water (up to 75 nM) and the overlying atmosphere (up to
1 ppbv) in the Canadian Arctic Archipelago (CAA). Furthermore, melt ponds,
which are widely prevalent, were identified as an important DMS source (with
DMS concentrations of up to 6 nM and a potential contribution to atmospheric
DMS of 20 % in the study area). (2)Â Evidence of widespread particle
nucleation and growth in the marine boundary layer was found in the CAA in
the summertime, with these events observed on 41 % of days in a 2016
cruise. As well, at Alert, Nunavut, particles that are newly formed and grown
under conditions of minimal anthropogenic influence during the months of July
and August are estimated to contribute 20 % to 80 % of the 30–50 nm
particle number density. DMS-oxidation-driven nucleation is facilitated by
the presence of atmospheric ammonia arising from seabird-colony emissions,
and potentially also from coastal regions, tundra, and biomass burning. Via
accumulation of secondary organic aerosol (SOA), a significant fraction of the new
particles grow to sizes that are active in cloud droplet formation. Although
the gaseous precursors to Arctic marine SOA remain poorly defined, the
measured levels of common continental SOA precursors (isoprene and
monoterpenes) were low, whereas elevated mixing ratios of oxygenated volatile
organic compounds (OVOCs) were inferred to arise via processes involving the
sea surface microlayer. (3)Â The variability in the vertical distribution of
black carbon (BC) under both springtime Arctic haze and more pristine
summertime aerosol conditions was observed. Measured particle size
distributions and mixing states were used to constrain, for the first time,
calculations of aerosol–climate interactions under Arctic conditions.
Aircraft- and ground-based measurements were used to better establish the BC
source regions that supply the Arctic via long-range transport mechanisms,
with evidence for a dominant springtime contribution from eastern and
southern Asia to the middle troposphere, and a major contribution from
northern Asia to the surface. (4)Â Measurements of ice nucleating particles
(INPs) in the Arctic indicate that a major source of these particles is
mineral dust, likely derived from local sources in the summer and long-range
transport in the spring. In addition, INPs are abundant in the sea surface
microlayer in the Arctic, and possibly play a role in ice nucleation in the
atmosphere when mineral dust concentrations are low. (5)Â Amongst multiple
aerosol components, BC was observed to have the smallest effective deposition
velocities to high Arctic snow (0.03 cm s−1).</p
Measurements of HCFC-22 and validation update
This talk reports about global HCFC-22 measurements derived from ACE-FTS occultation observations recorded from 2004 onwards. It further provides information on the validation of ACE-FTS products for CFC-11, -12 and HCFC-22 with ground-based FTIR instruments operated at four sites: Eureka, Poker Flat, Toronto and Jungfraujoch