69 research outputs found
Trajectory matching of ozonesondes and MOZAIC measurements in the UTLS â Part 2: Application to the global ozonesonde network
Both balloon-borne electrochemical ozonesondes and MOZAIC (measurements of
ozone, water vapour, carbon monoxide and nitrogen oxides by in-service Airbus
aircraft) provide very valuable data sets for ozone studies in the upper
troposphere/lower stratosphere (UTLS). Although MOZAIC's highly accurate
UV-photometers are regularly inspected and recalibrated annually, recent
analyses cast some doubt on the long-term stability of their ozone analysers.
To investigate this further, we perform a 16 yr comparison (1994â2009) of
UTLS ozone measurements from balloon-borne ozonesondes and MOZAIC. The
analysis uses fully three-dimensional trajectories computed from ERA-Interim
(European Centre for Medium-Range Weather Forecasts Re-analysis) wind fields
to find matches between the two measurement platforms. Although different
sensor types (Brewer-Mast and Electrochemical Concentration Cell ozonesondes)
were used, most of the 28 launch sites considered show considerable
differences of up to 25% compared to MOZAIC in the mid-1990s, followed
by a systematic tendency to smaller differences of around 5â10% in
subsequent years. The reason for the difference before 1998 remains unclear,
but observations from both sondes and MOZAIC require further examination to
be reliable enough for use in robust long-term trend analyses starting before
1998. According to our analysis, ozonesonde measurements at tropopause
altitudes appear to be rather insensitive to changing the type of the
Electrochemical Concentration Cell ozonesonde, provided the cathode sensing
solution strength remains unchanged. Scoresbysund (Greenland) showed
systematically 5% higher readings after changing from Science Pump
Corporation sondes to ENSCI Corporation sondes, while a 1.0% KI cathode
electrolyte was retained
The Upper Stratospheric Solar Cycle Ozone Response
The solar cycle (SC) stratospheric ozone response is thought to influence surface weather and climate. To understand the chain of processes and ensure climate models adequately represent them, it is important to detect and quantify an accurate SC ozone response from observations. Chemistry climate models (CCMs) and observations display a range of upper stratosphere (1â10 hPa) zonally averaged spatial responses; this and the recommended data set for comparison remains disputed. Recent dataâmerging advancements have led to more robust observational data. Using these data, we show that the observed SC signal exhibits an upper stratosphere Uâshaped spatial structure with lobes emanating from the tropics (5â10 hPa) to high altitudes at midlatitudes (1â3 hPa). We confirm this using two independent chemistry climate models in specified dynamics mode and an idealized timeslice experiment. We recommend the BASICv2 ozone composite to best represent historical upper stratospheric solar variability, and that those based on SBUV alone should not be used
Drivers of the tropospheric ozone budget throughout the 21st century under the medium-high climate scenario RCP 6.0
Because tropospheric ozone is both a greenhouse
gas and harmful air pollutant, it is important to understand
how anthropogenic activities may influence its abundance
and distribution through the 21st century. Here, we present
model simulations performed with the chemistryâclimate
model SOCOL, in which spatially disaggregated chemistry
and transport tracers have been implemented in order to better
understand the distribution and projected changes in tropospheric
ozone. We examine the influences of ozone precursor
emissions (nitrogen oxides (NOx /, carbon monoxide
(CO) and volatile organic compounds (VOCs)), climate
change (including methane effects) and stratospheric ozone
recovery on the tropospheric ozone budget, in a simulation
following the climate scenario Representative Concentration
Pathway (RCP) 6.0 (a medium-high, and reasonably realistic
climate scenario). Changes in ozone precursor emissions
have the largest effect, leading to a global-mean increase
in tropospheric ozone which maximizes in the early
21st century at 23% compared to 1960. The increase is
most pronounced at northern midlatitudes, due to regional
emission patterns: between 1990 and 2060, northern midlatitude
tropospheric ozone remains at constantly large abundances:
31% larger than in 1960. Over this 70-year period,
attempts to reduce emissions in Europe and North America
do not have an effect on zonally averaged northern midlatitude
ozone because of increasing emissions from Asia, together
with the long lifetime of ozone in the troposphere. A
simulation with fixed anthropogenic ozone precursor emissions
of NOx , CO and non-methane VOCs at 1960 conditions
shows a 6% increase in global-mean tropospheric ozone by
the end of the 21st century, with an 11% increase at northern
midlatitudes. This increase maximizes in the 2080s and
is mostly caused by methane, which maximizes in the 2080s
following RCP 6.0, and plays an important role in controlling
ozone directly, and indirectly through its influence on
other VOCs and CO. Enhanced flux of ozone from the stratosphere
to the troposphere as well as climate change-induced
enhancements in lightning NOx emissions also increase the
tropospheric ozone burden, although their impacts are relatively
small. Overall, the results show that under this climate
scenario, ozone in the future is governed largely by changes
in methane and NOx ; methane induces an increase in tropospheric
ozone that is approximately one-third of that caused
by NOx . Climate impacts on ozone through changes in tropospheric
temperature, humidity and lightning NOx remain
secondary compared with emission strategies relating to anthropogenic
emissions of NOx , such as fossil fuel burning.
Therefore, emission policies globally have a critical role to
play in determining tropospheric ozone evolution through the
21st century
Updated African biomass burning emission inventories in the framework of the AMMA-IDAF program, with an evaluation of combustion aerosols
African biomass burning emission inventories for gaseous and particulate species have been constructed at a resolution of 1 km by 1km with daily coverage for the 2000â2007 period. These inventories are higher than the GFED2 inventories, which are currently widely in use. Evaluation specifically focusing on combustion aerosol has been carried out with the ORISAM-TM4 global chemistry transport model which includes a detailed aerosol module. This paper compares modeled results with measurements of surface BC concentrations and scattering coefficients from the AMMA Enhanced Observations period, aerosol optical depths and single scattering albedo from AERONET sunphotometers, LIDAR vertical distributions of extinction coefficients as well as satellite data. Aerosol seasonal and interannual evolutions over the 2004â2007 period observed at regional scale and more specifically at the Djougou (Benin) and Banizoumbou (Niger) AMMA/IDAF sites are well reproduced by our global model, indicating that our biomass burning emission inventory appears reasonable
Evidence for a continuous decline in lower stratospheric ozone offsetting ozone layer recovery
Ozone forms in the Earth's atmosphere from the photodissociation of molecular oxygen, primarily in the tropical stratosphere. It is then transported to the extratropics by the BrewerâDobson circulation (BDC), forming a protective "ozone layer" around the globe. Human emissions of halogen-containing ozone-depleting substances (hODSs) led to a decline in stratospheric ozone until they were banned by the Montreal Protocol, and since 1998 ozone in the upper stratosphere is rising again, likely the recovery from halogen-induced losses. Total column measurements of ozone between the Earth's surface and the top of the atmosphere indicate that the ozone layer has stopped declining across the globe, but no clear increase has been observed at latitudes between 60°âŻS and 60°âŻN outside the polar regions (60â90°). Here we report evidence from multiple satellite measurements that ozone in the lower stratosphere between 60°âŻS and 60°âŻN has indeed continued to decline since 1998. We find that, even though upper stratospheric ozone is recovering, the continuing downward trend in the lower stratosphere prevails, resulting in a downward trend in stratospheric column ozone between 60°âŻS and 60°âŻN. We find that total column ozone between 60°âŻS and 60°âŻN appears not to have decreased only because of increases in tropospheric column ozone that compensate for the stratospheric decreases. The reasons for the continued reduction of lower stratospheric ozone are not clear; models do not reproduce these trends, and thus the causes now urgently need to be established
Earth system science frontiers - an early career perspective
The exigencies of the global community toward Earth system science will increase in the future as the human population, economies, and the human footprint on the planet continue to grow. This growth, combined with intensifying urbanization, will inevitably exert increasing pressure on all ecosystem services. A unified interdisciplinary approach to Earth system science is required that can address this challenge, integrate technical demands and long-term visions, and reconcile user demands with scientific feasibility. Together with the research arms of the World Meteorological Organization, the Young Earth System Scientists community has gathered early-career scientists from around the world to initiate a discussion about frontiers of Earth system science. To provide optimal information for society, Earth system science has to provide a comprehensive understanding of the physical processes that drive the Earth system and anthropogenic influences. This understanding will be reflected in seamless prediction systems for environmental processes that are robust and instructive to local users on all scales. Such prediction systems require improved physical process understanding, more high-resolution global observations, and advanced modeling capability, as well as high-performance computing on unprecedented scales. At the same time, the robustness and usability of such prediction systems also depend on deepening our understanding of the entire Earth system and improved communication between end users and researchers. Earth system science is the fundamental baseline for understanding the Earthâs capacity to accommodate humanity, and it provides a means to have a rational discussion about the consequences and limits of anthropogenic influence on Earth. Without its progress, truly sustainable development will be impossible. © 2017 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses)
Real-time pollen identification using holographic imaging and fluorescence measurements
Over the past few years, a diverse range of automatic real-time instruments has been developed to respond to the needs of end users in terms of information about atmospheric bioaerosols. One of them, the SwisensPoleno Jupiter, is an airflow cytometer used for operational automatic bioaerosol monitoring. The instrument records holographic images and fluorescence information for single aerosol particles, which can be used for identification of several aerosol types, in particular different pollen taxa. To improve the pollen identification algorithm applied to the SwisensPoleno Jupiter and currently based only on the holography data, we explore the impact of merging fluorescence spectra measurements with holographic images. We demonstrate, using measurements of aerosolised pollen, that combining information from these two sources results in a considerable improvement in the classification performance compared to using only a single source (balanced accuracy of 0.992 vs. 0.968 and 0.878). This increase in performance can be ascribed to the fact that often classes which are difficult to resolve using holography alone can be well identified using fluorescence and vice versa. We also present a detailed statistical analysis of the features of the pollen grains that are measured and provide a robust, physically based insight into the algorithm's identification process. The results are expected to have a direct impact on operational pollen identification models, particularly improving the recognition of taxa responsible for respiratory allergies.</p
Atmospheric isoprene measurements reveal larger-than-expected Southern Ocean emissions
Isoprene is a key trace component of the atmosphere emitted by vegetation and other organisms. It is highly reactive and can impact atmospheric composition and climate by affecting the greenhouse gases ozone and methane and secondary organic aerosol formation. Marine fluxes are poorly constrained due to the paucity of long-term measurements; this in turn limits our understanding of isoprene cycling in the ocean. Here we present the analysis of isoprene concentrations in the atmosphere measured across the Southern Ocean over 4 months in the summertime. Some of the highest concentrations (â>500 ppt) originated from the marginal ice zone in the Ross and Amundsen seas, indicating the marginal ice zone is a significant source of isoprene at high latitudes. Using the United Kingdom Earth System Model we show that current estimates of sea-to-air isoprene fluxes underestimate observed isoprene by a factor >20. A daytime source of isoprene is required to reconcile models with observations. The model presented here suggests such an increase in isoprene emissions would lead to >8% decrease in the hydroxyl radical in regions of the Southern Ocean, with implications for our understanding of atmospheric oxidation and composition in remote environments, often used as proxies for the pre-industrial atmosphere
Deriving Global OH Abundance and Atmospheric Lifetimes for Long-Lived Gases: A Search for CH 3 CCl 3 Alternatives
An accurate estimate of global hydroxyl radical (OH) abundance is important for projections of air quality, climate, and stratospheric ozone recovery. As the atmospheric mixing ratios of methyl chloroform (CHâCClâ) (MCF), the commonly used OH reference gas, approaches zero, it is important to find alternative approaches to infer atmospheric OH abundance and variability. The lack of global bottomâup emission inventories is the primary obstacle in choosing a MCF alternative. We illustrate that global emissions of longâlived trace gases can be inferred from their observed mixing ratio differences between the Northern Hemisphere (NH) and Southern Hemisphere (SH), given realistic estimates of their NHâSH exchange time, the emission partitioning between the two hemispheres, and the NH versus SH OH abundance ratio. Using the observed longâterm trend and emissions derived from the measured hemispheric gradient, the combination of HFCâ32 (CHâFâ), HFCâ134a (CHâFCFâ, HFCâ152a (CHâCHFâ), and HCFCâ22 (CHClFâ), instead of a single gas, will be useful as a MCF alternative to infer global and hemispheric OH abundance and trace gas lifetimes. The primary assumption on which this multispecies approach relies is that the OH lifetimes can be estimated by scaling the thermal reaction rates of a reference gas at 272 K on global and hemispheric scales. Thus, the derived hemispheric and global OH estimates are forced to reconcile the observed trends and gradient for all four compounds simultaneously. However, currently, observations of these gases from the surface networks do not provide more accurate OH abundance estimate than that from MCF
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