31 research outputs found
Analysis of ozone and nitric acid in spring and summer Arctic pollution using aircraft, ground-based, satellite observations and MOZART-4 model: source attribution and partitioning
In this paper, we analyze tropospheric O_3 together with HNO_3 during the POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols, and Transport) program, combining observations and model results. Aircraft observations from the NASA ARCTAS (Arctic Research of the Composition of the Troposphere from Aircraft and Satellites) and NOAA ARCPAC (Aerosol, Radiation and Cloud Processes affecting Arctic Climate) campaigns during spring and summer of 2008 are used together with the Model for Ozone and Related Chemical Tracers, version 4 (MOZART-4) to assist in the interpretation of the observations in terms of the source attribution and transport of O_3 and HNO_3 into the Arctic (north of 60° N). The MOZART-4 simulations reproduce the aircraft observations generally well (within 15%), but some discrepancies in the model are identified and discussed. The observed correlation of O_3 with HNO_3 is exploited to evaluate the MOZART-4 model performance for different air mass types (fresh plumes, free troposphere and stratospheric-contaminated air masses).
Based on model simulations of O_3 and HNO_3 tagged by source type and region, we find that the anthropogenic pollution from the Northern Hemisphere is the dominant source of O3 and HNO3 in the Arctic at pressures greater than 400 hPa, and that the stratospheric influence is the principal contribution at pressures less 400 hPa. During the summer, intense Russian fire emissions contribute some amount to the tropospheric columns of both gases over the American sector of the Arctic. North American fire emissions (California and Canada) also show an important impact on tropospheric ozone in the Arctic boundary layer.
Additional analysis of tropospheric O_3 measurements from ground-based FTIR and from the IASI satellite sounder made at the Eureka (Canada) and Thule (Greenland) polar sites during POLARCAT has been performed using the tagged contributions. It demonstrates the capability of these instruments for observing pollution at northern high latitudes. Differences between contributions from the sources to the tropospheric columns as measured by FTIR and IASI are discussed in terms of vertical sensitivity associated with these instruments. The first analysis of O_3 tropospheric columns observed by the IASI satellite instrument over the Arctic is also provided. Despite its limited vertical sensitivity in the lowermost atmospheric layers, we demonstrate that IASI is capable of detecting low-altitude pollution transported into the Arctic with some limitations
The influence of boreal biomass burning emissions on the distribution of tropospheric ozone over North America and the North Atlantic during 2010
We have analysed the sensitivity of the tropospheric ozone distribution over North America and the North Atlantic to boreal biomass burning emissions during the summer of 2010 using the GEOS-Chem 3-D global tropospheric chemical transport model and observations from in situ and satellite instruments. We show that the model ozone distribution is consistent with observations from the Pico Mountain Observatory in the Azores, ozonesondes across Canada, and the Tropospheric Emission Spectrometer (TES) and Infrared Atmospheric Sounding Instrument (IASI) satellite instruments. Mean biases between the model and observed ozone mixing ratio in the free troposphere were less than 10 ppbv. We used the adjoint of GEOS-Chem to show the model ozone distribution in the free troposphere over Maritime Canada is largely sensitive to NO<sub>x</sub> emissions from biomass burning sources in Central Canada, lightning sources in the central US, and anthropogenic sources in the eastern US and south-eastern Canada. We also used the adjoint of GEOS-Chem to evaluate the Fire Locating And Monitoring of Burning Emissions (FLAMBE) inventory through assimilation of CO observations from the Measurements Of Pollution In The Troposphere (MOPITT) satellite instrument. The CO inversion showed that, on average, the FLAMBE emissions needed to be reduced to 89% of their original values, with scaling factors ranging from 12% to 102%, to fit the MOPITT observations in the boreal regions. Applying the CO scaling factors to all species emitted from boreal biomass burning sources led to a decrease of the model tropospheric distributions of CO, PAN, and NO<sub>x</sub> by as much as −20 ppbv, −50 pptv, and −20 pptv respectively. The modification of the biomass burning emission estimates reduced the model ozone distribution by approximately −3 ppbv (−8%) and on average improved the agreement of the model ozone distribution compared to the observations throughout the free troposphere, reducing the mean model bias from 5.5 to 4.0 ppbv for the Pico Mountain Observatory, 3.0 to 0.9 ppbv for ozonesondes, 2.0 to 0.9 ppbv for TES, and 2.8 to 1.4 ppbv for IASI
The influence of boreal biomass burning emissions on the distribution of tropospheric ozone over North America and the North Atlantic during 2010
We have analysed the sensitivity of the tropospheric ozone distribution over North America and the North Atlantic to boreal biomass burning emissions during the summer of 2010 using the GEOS-Chem 3-D global tropospheric chemical transport model and observations from in situ and satellite instruments. We show that the model ozone distribution is consistent with observations from the Pico Mountain Observatory in the Azores, ozonesondes across Canada, and the Tropospheric Emission Spectrometer (TES) and Infrared Atmospheric Sounding Instrument (IASI) satellite instruments. Mean biases between the model and observed ozone mixing ratio in the free troposphere were less than 10 ppbv. We used the adjoint of GEOS-Chem to show the model ozone distribution in the free troposphere over Maritime Canada is largely sensitive to NOx emissions from biomass burning sources in Central Canada, lightning sources in the central US, and anthropogenic sources in the eastern US and south-eastern Canada. We also used the adjoint of GEOS-Chem to evaluate the Fire Locating And Monitoring of Burning Emissions (FLAMBE) inventory through assimilation of CO observations from the Measurements Of Pollution In The Troposphere (MOPITT) satellite instrument. The CO inversion showed that, on average, the FLAMBE emissions needed to be reduced to 89% of their original values, with scaling factors ranging from 12% to 102%, to fit the MOPITT observations in the boreal regions. Applying the CO scaling factors to all species emitted from boreal biomass burning sources led to a decrease of the model tropospheric distributions of CO, PAN, and NOx by as much as -20 ppbv, -50 pptv, and -20 pptv respectively. The modification of the biomass burning emission estimates reduced the model ozone distribution by approximately -3 ppbv (-8%) and on average improved the agreement of the model ozone distribution compared to the observations throughout the free troposphere, reducing the mean model bias from 5.5 to 4.0 ppbv for the Pico Mountain Observatory, 3.0 to 0.9 ppbv for ozonesondes, 2.0 to 0.9 ppbv for TES, and 2.8 to 1.4 ppbv for IASI
Validation of the IASI FORLI/EUMETSAT ozone products using satellite (GOME-2), ground-based (Brewer–Dobson, SAOZ, FTIR) and ozonesonde measurements
This paper assesses the quality of IASI (Infrared Atmospheric Sounding Interferometer)/Metop-A (IASI-A) and
IASI/Metop-B (IASI-B) ozone (O3) products (total and partial
O3 columns) retrieved with the Fast Optimal Retrievals on Layers
for IASI Ozone (FORLI-O3; v20151001) software for 9 years
(2008–July 2017) through an extensive intercomparison and validation
exercise using independent observations (satellite, ground-based and
ozonesonde). Compared with the previous version of FORLI-O3 (v20140922),
several improvements have been introduced in FORLI-O3 v20151001,
including absorbance look-up tables recalculated to cover a larger spectral
range, with additional numerical corrections. This leads to a change of ∼ 4 % in the total ozone column (TOC) product, which is mainly associated
with a decrease in the retrieved O3 concentration in the middle
stratosphere (above 30 hPa/25 km). IASI-A and IASI-B TOCs are consistent,
with a global mean difference of less than 0.3 % for both daytime and
nighttime measurements; IASI-A is slightly higher than IASI-B. A global
difference of less than 2.4 % is found for the tropospheric (TROPO)
O3 column product (IASI-A is lower than IASI-B), which is partly
due to a temporary issue related to the IASI-A viewing angle in 2015. Our
validation shows that IASI-A and IASI-B TOCs are consistent with
GOME-2 (Global Ozone Monitoring Experiment-2), Dobson, Brewer, SAOZ
(Système d'Analyse par Observation
Zénithale) and FTIR (Fourier transform infrared)
TOCs, with global mean differences in the range of 0.1 %–2 %
depending on the instruments compared. The worst agreement with UV–vis
retrieved TOC (satellite and ground) is found at the southern high latitudes.
The IASI-A and ground-based TOC comparison for the period from 2008 to July
2017 shows the long-term stability of IASI-A, with insignificant or small negative
drifts of 1 %–3 % decade−1. The comparison results of IASI-A and IASI-B
against smoothed FTIR and ozonesonde partial O3 columns vary with
altitude and latitude, with the maximum standard deviation being seen for the
300–150 hPa column (20 %–40 %) due to strong ozone variability and
large total retrievals errors. Compared with ozonesonde data, the IASI-A and
IASI-B O3 TROPO column (defined as the column between the surface
and 300 hPa) is positively biased in the high latitudes (4 %–5 %)
and negatively biased in the midlatitudes and tropics (11 %–13 % and
16 %–19 %, respectively). The IASI-A-to-ozonesonde TROPO comparison
for the period from 2008 to 2016 shows a significant negative drift in the
Northern Hemisphere of −8.6±3.4 % decade−1, which is also
found in the IASI-A-to-FTIR TROPO comparison. When considering the period
from 2011 to 2016, the drift value for the TROPO column decreases and becomes
statistically insignificant. The observed negative drifts of the IASI-A TROPO
O3 product (8 %–16 % decade−1) over the 2008–2017
period might be taken into consideration when deriving trends from this
product and this time period.</p
Tropospheric Ozone Assessment Report: Present-day distribution and trends of tropospheric ozone relevant to climate and global atmospheric chemistry model evaluation
The Tropospheric Ozone Assessment Report (TOAR) is an activity of the International Global Atmospheric Chemistry Project. This paper is a component of the report, focusing on the present-day distribution and trends of tropospheric ozone relevant to climate and global atmospheric chemistry model evaluation. Utilizing the TOAR surface ozone database, several figures present the global distribution and trends of daytime average ozone at 2702 non-urban monitoring sites, highlighting the regions and seasons of the world with the greatest ozone levels. Similarly, ozonesonde and commercial aircraft observations reveal ozone’s distribution throughout the depth of the free troposphere. Long-term surface observations are limited in their global spatial coverage, but data from remote locations indicate that ozone in the 21st century is greater than during the 1970s and 1980s. While some remote sites and many sites in the heavily polluted regions of East Asia show ozone increases since 2000, many others show decreases and there is no clear global pattern for surface ozone changes since 2000. Two new satellite products provide detailed views of ozone in the lower troposphere across East Asia and Europe, revealing the full spatial extent of the spring and summer ozone enhancements across eastern China that cannot be assessed from limited surface observations. Sufficient data are now available (ozonesondes, satellite, aircraft) across the tropics from South America eastwards to the western Pacific Ocean, to indicate a likely tropospheric column ozone increase since the 1990s. The 2014–2016 mean tropospheric ozone burden (TOB) between 60˚N–60˚S from five satellite products is 300 Tg ± 4%. While this agreement is excellent, the products differ in their quantification of TOB trends and further work is required to reconcile the differences. Satellites can now estimate ozone’s global long-wave radiative effect, but evaluation is difficult due to limited in situ observations where the radiative effect is greatest
Quality assessment of the Ozone_cci Climate Research Data Package (release 2017) – Part 2: Ground-based validation of nadir ozone profile data products
Atmospheric ozone plays a key role in
air quality and the radiation budget of the Earth, both directly and through
its chemical influence on other trace gases. Assessments of the atmospheric
ozone distribution and associated climate change therefore demand accurate
vertically resolved ozone observations with both stratospheric and
tropospheric sensitivity, on both global and regional scales, and both in the
long term and at shorter timescales. Such observations have been acquired by
two series of European nadir-viewing ozone profilers, namely the
scattered-light UV–visible spectrometers of the GOME family, launched
regularly since 1995 (GOME, SCIAMACHY, OMI, GOME-2A/B, TROPOMI, and the
upcoming Sentinel-5 series), and the thermal infrared emission sounders of
the IASI type, launched regularly since 2006 (IASI on Metop platforms and the
upcoming IASI-NG on Metop-SG). In particular, several Level-2 retrieved,
Level-3 monthly gridded, and Level-4 assimilated nadir ozone profile data
products have been improved and harmonized in the context of the ozone
project of the European Space Agency's Climate Change Initiative (ESA
Ozone_cci). To verify their fitness for purpose, these ozone datasets must
undergo a comprehensive quality assessment (QA), including (a) detailed
identification of their geographical, vertical, and temporal domains of
validity; (b) quantification of their potential bias, noise, and drift and
their dependences on major influence quantities; and (c) assessment of the
mutual consistency of data from different sounders. For this purpose we have
applied to the Ozone_cci Climate Research Data Package (CRDP) released in
2017 the versatile QA and validation system Multi-TASTE, which has been
developed in the context of several heritage projects (ESA's Multi-TASTE,
EUMETSAT's O3M-SAF, and the European Commission's FP6 GEOmon and FP7 QA4ECV).
This work, as the second in a series of four Ozone_cci validation papers,
reports for the first time on data content studies, information content
studies and ground-based validation for both the GOME- and IASI-type climate
data records combined. The ground-based reference measurements have been
provided by the Network for the Detection of Atmospheric Composition
Change (NDACC), NASA's Southern Hemisphere Additional Ozonesonde
programme (SHADOZ), and other ozonesonde and lidar stations contributing to
the World Meteorological Organisation's Global Atmosphere Watch (WMO GAW).
The nadir ozone profile CRDP quality assessment reveals that all nadir ozone
profile products under study fulfil the GCOS user requirements in terms of
observation frequency and horizontal and vertical resolution. Yet all
L2 observations also show sensitivity outliers in the UTLS and are strongly
correlated vertically due to substantial averaging kernel fluctuations that
extend far beyond the kernel's 15 km FWHM. The CRDP typically does not
comply with the GCOS user requirements in terms of total uncertainty and
decadal drift, except for the UV–visible L4 dataset. The drift values of the
L2 GOME and OMI, the L3 IASI, and the L4 assimilated products are found to be
overall insignificant, however, and applying appropriate altitude-dependent
bias and drift corrections make the data fit for climate and atmospheric
composition monitoring and modelling purposes. Dependence of the Ozone_cci
data quality on major influence quantities – resulting in data screening
suggestions to users – and perspectives for the Copernicus Sentinel missions
are additionally discussed
Tropospheric Ozone Assessment Report: Present-day distribution and trends of tropospheric ozone relevant to climate and global atmospheric chemistry model evaluation
The Tropospheric Ozone Assessment Report (TOAR) is an activity of the International Global Atmospheric Chemistry Project. This paper is a component of the report, focusing on the present-day distribution and trends of tropospheric ozone relevant to climate and global atmospheric chemistry model evaluation. Utilizing the TOAR surface ozone database, several figures present the global distribution and trends of daytime average ozone at 2702 non-urban monitoring sites, highlighting the regions and seasons of the world with the greatest ozone levels. Similarly, ozonesonde and commercial aircraft observations reveal ozone’s distribution throughout the depth of the free troposphere. Long-term surface observations are limited in their global spatial coverage, but data from remote locations indicate that ozone in the 21st century is greater than during the 1970s and 1980s. While some remote sites and many sites in the heavily polluted regions of East Asia show ozone increases since 2000, many others show decreases and there is no clear global pattern for surface ozone changes since 2000. Two new satellite products provide detailed views of ozone in the lower troposphere across East Asia and Europe, revealing the full spatial extent of the spring and summer ozone enhancements across eastern China that cannot be assessed from limited surface observations. Sufficient data are now available (ozonesondes, satellite, aircraft) across the tropics from South America eastwards to the western Pacific Ocean, to indicate a likely tropospheric column ozone increase since the 1990s. The 2014–2016 mean tropospheric ozone burden (TOB) between 60˚N–60˚S from five satellite products is 300 Tg ± 4%. While this agreement is excellent, the products differ in their quantification of TOB trends and further work is required to reconcile the differences. Satellites can now estimate ozone’s global long-wave radiative effect, but evaluation is difficult due to limited in situ observations where the radiative effect is greatest
Fourier transform measurement of NO2 absorption cross-section in the visible range at room temperature
TAU-CLUSTERING, ANOMALIES AND FORBIDDEN FEATURES IN THE -ROCKING AND OH-BENDING BANDS OF
Author Institution: Centre for Laser Applications and Molecular Science (CLAMS), Department of Physics, University of Brunswick; CLAMS and Department of Physical Sciences, University of New Brunswick; Steacie Institute for Molecular Sciences, National Research Council CanadaThe -rocking and OH-bending bands are being investigated in high-resolution Fourier transform spectra of . For the in-plane -rock, subbands have been assigned with origins clustered around for the ground torsional state and around 1100 for the torsionally excited state. The subbands are stronger than the series, suggesting that intensity borrowing is taking place through vibrational mixing of the rocking states with nearby OH-bend and CO-stretch levels. This idea is supported by observation of forbidden subbands from ground-state levels to rocking levels. For the OH-bending fundamental, the subbands are relatively widely distributed over the 1315-1347 region with the characteristic grouping into two -clusters found when the torsional barrier changes significantly. However, the subband origins imply an inverted excited-state energy pattern compared to the usual model, hence the actual torsional barrier height for the OH-bending state is a matter of conjecture. Again, forbidden subbands are seen below the main OH-bending series. Interesting anomalous splittings and intensities are also observed for certain of the K-doublets in all of the vibrational bands. As we continue to build our knowledge of the details and the novel features of the torsion-vibration-rotation energy level manifold of the CO-stretch, -rock and OH-bend modes of , more and more interactions are revealed which couple the states and can contirbute to IVR rates in methanol. We are aiming to quantify the degree of mixing and the magnitude of the coupling by examining the relative intensities of allowed and forbidden transitions. We will also look at the relative strengths of parallel and perpendicular transitions in the -rocking band to seek further insight into the nature of the -rocking normal mode and the origin of the substantial parallel transition moment