103 research outputs found
Population exposure to hazardous air quality due to the 2015 fires in Equatorial Asia.
Vegetation and peatland fires cause poor air quality and thousands of premature deaths across densely populated regions in Equatorial Asia. Strong El-Niño and positive Indian Ocean Dipole conditions are associated with an increase in the frequency and intensity of wildfires in Indonesia and Borneo, enhancing population exposure to hazardous concentrations of smoke and air pollutants. Here we investigate the impact on air quality and population exposure of wildfires in Equatorial Asia during Fall 2015, which were the largest over the past two decades. We performed high-resolution simulations using the Weather Research and Forecasting model with Chemistry based on a new fire emission product. The model captures the spatio-temporal variability of extreme pollution episodes relative to space- and ground-based observations and allows for identification of pollution sources and transport over Equatorial Asia. We calculate that high particulate matter concentrations from fires during Fall 2015 were responsible for persistent exposure of 69 million people to unhealthy air quality conditions. Short-term exposure to this pollution may have caused 11,880 (6,153-17,270) excess mortalities. Results from this research provide decision-relevant information to policy makers regarding the impact of land use changes and human driven deforestation on fire frequency and population exposure to degraded air quality.This research was supported in part by a L’Oréal-UNESCO UK and Ireland Fellowship For Women In Science (to PC), the Natural Environmental Research Council (NERC) through the LICS the SAMBBA project (ref. NE/J009822/1), the EPA STAR program (R835422), and the National Research Fellow Award (NRF2012NRFNRFF001-031). EB is partly supported by funding from UBoC. Further support was provided by the Lilly Endowment, Inc., through its support for the Indiana University Pervasive Technology Institute and the Indiana METACyt Initiative. This work makes use of the LandScan (2013)™ High Resolution global Population Data Set copyrighted by UT-Battelle, LLC, operator of Oak Ridge National Laboratory under Contract No. DE-AC05- 00OR22725 with the United States Department of Energy. Global Burden of Disease used in this study have been accessed from the Institute for Health Metric and Evaluation website: http://ghdx.healthdata.org/ihme_data. We gratefully acknowledge the National Environment Agency (NEA) of Singapore for collecting and providing PM2.5 and PSI data (available at http://www.nea.gov.sg/anti-pollution-radiation-protection/air-pollution-control/psi/historical-psi-readings). The National Center for Atmospheric Research is operated by the University Corporation for Atmospheric Research under the sponsorship of the National Science Foundation. We thank Louisa Emmons for providing the boundary conditions for dust from CAM-Chem. We also acknowledge the NASA scientists responsible for MODIS products, WRF-Chem developers and ACOM scientists at NCAR for useful discussion on model set-up
ROOOH: A missing piece of the puzzle for OH measurements in low-NO environments?
Abstract. Field campaigns have been carried out with the FAGE (fluorescence assay by
gas expansion) technique in remote biogenic environments in the last decade
to quantify the in situ concentrations of OH, the main oxidant in the
atmosphere. These data have revealed concentrations of OH radicals up to a
factor of 10 higher than predicted by models, whereby the disagreement
increases with decreasing NO concentration. This was interpreted as a major
lack in our understanding of the chemistry of biogenic VOCs (volatile organic
compounds), particularly isoprene, which are dominant in remote pristine
conditions. But interferences in these measurements of unknown origin have
also been discovered for some FAGE instruments: using a pre-injector, all
ambient OH is removed by fast reaction before entering the FAGE cell, and any
remaining OH signal can be attributed to an interference. This technique is
now systematically used for FAGE measurements, allowing the reliable
quantification of ambient OH concentrations along with the signal due to
interference OH. However, the disagreement between modelled and measured high
OH concentrations of earlier field campaigns as well as the origin of the
now-quantifiable background OH is still not understood. We present in this
paper the compelling idea that this interference, and thus the disagreement
between model and measurement in earlier field campaigns, might be at least
partially due to the unexpected decomposition of a new class of molecule,
ROOOH, within the FAGE instruments. This idea is based on experiments,
obtained with the FAGE set-up of the University of Lille, and supported by a
modelling study. Even though the occurrence of this interference will be
highly dependent on the design and measurement conditions of different FAGE
instruments, including ROOOH in atmospheric chemistry models might reflect a
missing piece of the puzzle in our understanding of OH in clean atmospheres.
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WRF-Chem model predictions of the regional impacts of N2O5 heterogeneous processes on night-time chemistry over north-western Europe
Abstract. Chemical modelling studies have been conducted over north-western Europe in summer conditions, showing that night-time dinitrogen pentoxide (N2O5) heterogeneous reactive uptake is important regionally in modulating particulate nitrate and has a~modest influence on oxidative chemistry. Results from Weather Research and Forecasting model with Chemistry (WRF-Chem) model simulations, run with a detailed volatile organic compound (VOC) gas-phase chemistry scheme and the Model for Simulating Aerosol Interactions and Chemistry (MOSAIC) sectional aerosol scheme, were compared with a series of airborne gas and particulate measurements made over the UK in July 2010. Modelled mixing ratios of key gas-phase species were reasonably accurate (correlations with measurements of 0.7–0.9 for NO2 and O3). However modelled loadings of particulate species were less accurate (correlation with measurements for particulate sulfate and ammonium were between 0.0 and 0.6). Sulfate mass loadings were particularly low (modelled means of 0.5–0.7 μg kg−1air, compared with measurements of 1.0–1.5 μg kg−1air). Two flights from the campaign were used as test cases – one with low relative humidity (RH) (60–70%), the other with high RH (80–90%). N2O5 heterogeneous chemistry was found to not be important in the low-RH test case; but in the high-RH test case it had a strong effect and significantly improved the agreement between modelled and measured NO3 and N2O5. When the model failed to capture atmospheric RH correctly, the modelled NO3 and N2O5 mixing ratios for these flights differed significantly from the measurements. This demonstrates that, for regional modelling which involves heterogeneous processes, it is essential to capture the ambient temperature and water vapour profiles. The night-time NO3 oxidation of VOCs across the whole region was found to be 100–300 times slower than the daytime OH oxidation of these compounds. The difference in contribution was less for alkenes (× 80) and comparable for dimethylsulfide (DMS). However the suppression of NO3 mixing ratios across the domain by N2O5 heterogeneous chemistry has only a very slight, negative, influence on this oxidative capacity. The influence on regional particulate nitrate mass loadings is stronger. Night-time N2O5 heterogeneous chemistry maintains the production of particulate nitrate within polluted regions: when this process is taken into consideration, the daytime peak (for the 95th percentile) of PM10 nitrate mass loadings remains around 5.6 μg kg−1air, but the night-time minimum increases from 3.5 to 4.6 μg kg−1air. The sustaining of higher particulate mass loadings through the night by this process improves model skill at matching measured aerosol nitrate diurnal cycles and will negatively impact on regional air quality, requiring this process to be included in regional models.
This work was supported by the NERC RONOCO project NE/F004656/1.
S. Archer-Nicholls was supported by a NERC quota studentship.This is the final version of the article. It first appeared at http://www.atmos-chem-phys.net/15/1385/2015/acp-15-1385-2015.pd
Chemistry-driven changes strongly influence climate forcing from vegetation emissions
Biogenic volatile organic compounds (BVOCs) affect climate via changes to aerosols, aerosol-cloud interactions (ACI), ozone and methane. BVOCs exhibit dependence on climate (causing a feedback) and land use but there remains uncertainty in their net climatic impact. One factor is the description of BVOC chemistry. Here, using the earth-system model UKESM1, we quantify chemistry’s influence by comparing the response to doubling BVOC emissions in the pre-industrial with standard and state-of-science chemistry. The net forcing (feedback) is positive: ozone and methane increases and ACI changes outweigh enhanced aerosol scattering. Contrary to prior studies, the ACI response is driven by cloud droplet number concentration (CDNC) reductions from suppression of gas-phase SO2 oxidation. With state-of-science chemistry the feedback is 43% smaller as lower oxidant depletion yields smaller methane increases and CDNC decreases. This illustrates chemistry’s significant influence on BVOC’s climatic impact and the more complex pathways by which BVOCs influence climate than currently recognised
Development, intercomparison, and evaluation of an improved mechanism for the oxidation of dimethyl sulfide in the UKCA model
Dimethyl sulfide (DMS) is an important trace gas emitted from the ocean. The oxidation of DMS has long been recognised as being important for global climate through the role DMS plays in setting the sulfate aerosol background in the troposphere. However, the mechanisms in which DMS is oxidised are very complex and have proved elusive to accurately determine in spite of decades of research. As a result the representation of DMS oxidation in global chemistry–climate models is often greatly simplified.
Recent field observations and laboratory and ab initio studies have prompted renewed efforts in understanding the DMS oxidation mechanism, with implications for constraining the uncertainty in the oxidation mechanism of DMS as incorporated in global chemistry–climate models. Here we build on recent evidence and develop a new DMS mechanism for inclusion in the UK Chemistry Aerosol (UKCA) chemistry–climate model. We compare our new mechanism (CS2-HPMTF) to a number of existing mechanisms used in UKCA (including the highly simplified three-reactions–two-species mechanism used in CMIP6 studies with the model) and to a range of recently developed mechanisms reported in the literature through a series of global and box model experiments. Global model runs with the new mechanism enable us to simulate the global distribution of hydroperoxylmethyl thioformate (HPMTF), which we calculate to have a burden of 2.6–26 Gg S (in good agreement with the literature range of 0.7–18 Gg S). We show that the sinks of HPMTF dominate uncertainty in the budget, not the rate of the isomerisation reaction forming it and that, based on the observed DMS / HPMTF ratio from the global surveys during the NASA Atmospheric Tomography mission (ATom), rapid cloud uptake of HPMTF worsens the model–observation comparison. Our box model experiments highlight that there is significant variance in simulated secondary oxidation products from DMS across mechanisms used in the literature, with significant divergence in the sensitivity of the rates of formation of these products to temperature exhibited; especially for methane sulfonic acid (MSA). Our global model studies show that our updated DMS scheme performs better than the current scheme used in UKCA when compared against a suite of surface and aircraft observations. However, sensitivity studies underscore the need for further laboratory and observational constraints. In particular our results suggest that as a priority long-term DMS observations be made to better constrain the highly uncertain inputs into the system and that laboratory studies be performed that address (1) the uptake of HPMTF onto aerosol surfaces and the products of this reaction and (2) the kinetics and products of the following reactions: CH3SO3 decomposition, CH3S + O2, CH3SOO decomposition, and CH3SO + O3.</p
Development, intercomparison, and evaluation of an improved mechanism for the oxidation of dimethyl sulfide in the UKCA model
Dimethyl sulfide (DMS) is an important trace gas emitted from the ocean. The oxidation of DMS has long been recognised as being important for global climate through the role DMS plays in setting the sulfate aerosol background in the troposphere. However, the mechanisms in which DMS is oxidised are very complex and have proved elusive to accurately determine in spite of decades of research. As a result the representation of DMS oxidation in global chemistry–climate models is often greatly simplified. Recent field observations and laboratory and ab initio studies have prompted renewed efforts in understanding the DMS oxidation mechanism, with implications for constraining the uncertainty in the oxidation mechanism of DMS as incorporated in global chemistry–climate models. Here we build on recent evidence and develop a new DMS mechanism for inclusion in the UK Chemistry Aerosol (UKCA) chemistry–climate model. We compare our new mechanism (CS2-HPMTF) to a number of existing mechanisms used in UKCA (including the highly simplified three-reactions–two-species mechanism used in CMIP6 studies with the model) and to a range of recently developed mechanisms reported in the literature through a series of global and box model experiments. Global model runs with the new mechanism enable us to simulate the global distribution of hydroperoxylmethyl thioformate (HPMTF), which we calculate to have a burden of 2.6–26 Gg S (in good agreement with the literature range of 0.7–18 Gg S). We show that the sinks of HPMTF dominate uncertainty in the budget, not the rate of the isomerisation reaction forming it and that, based on the observed DMS / HPMTF ratio from the global surveys during the NASA Atmospheric Tomography mission (ATom), rapid cloud uptake of HPMTF worsens the model–observation comparison. Our box model experiments highlight that there is significant variance in simulated secondary oxidation products from DMS across mechanisms used in the literature, with significant divergence in the sensitivity of the rates of formation of these products to temperature exhibited; especially for methane sulfonic acid (MSA). Our global model studies show that our updated DMS scheme performs better than the current scheme used in UKCA when compared against a suite of surface and aircraft observations. However, sensitivity studies underscore the need for further laboratory and observational constraints. In particular our results suggest that as a priority long-term DMS observations be made to better constrain the highly uncertain inputs into the system and that laboratory studies be performed that address (1) the uptake of HPMTF onto aerosol surfaces and the products of this reaction and (2) the kinetics and products of the following reactions: CH3SO3 decomposition, CH3S + O2, CH3SOO decomposition, and CH3SO + O3
The Family Name as Socio-Cultural Feature and Genetic Metaphor: From Concepts to Methods
A recent workshop entitled The Family Name as Socio-Cultural Feature and Genetic Metaphor: From Concepts to Methods was held in Paris in December 2010, sponsored by the French National Centre for Scientific Research (CNRS) and by the journal Human Biology. This workshop was intended to foster a debate on questions related to the family names and to compare different multidisciplinary approaches involving geneticists, historians, geographers, sociologists and social anthropologists. This collective paper presents a collection of selected communications
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Description and evaluation of the UKCA stratosphere-troposphere chemistry scheme (StratTrop vn 1.0) implemented in UKESM1
Abstract. Here we present a description of the UKCA StratTrop chemical mechanism, which is used in the UKESM1 Earth system model for CMIP6. The StratTrop chemical mechanism is a merger of previously well-evaluated tropospheric and stratospheric mechanisms, and we provide results from a series of bespoke integrations to assess the overall performance of the model. We find that the StratTrop scheme performs well when compared to a wide
array of observations. The analysis we present here focuses on key
components of atmospheric composition, namely the performance of the model
to simulate ozone in the stratosphere and troposphere and constituents that
are important for ozone in these regions. We find that the results obtained
for tropospheric ozone and its budget terms from the use of the StratTrop
mechanism are sensitive to the host model; simulations with the same
chemical mechanism run in an earlier version of the MetUM host model show a
range of sensitivity to emissions that the current model does not fall
within. Whilst the general model performance is suitable for use in the UKESM1 CMIP6 integrations, we note some shortcomings in the scheme that future targeted studies will address.
NERC (NE/M00273X/1), NERC (NE/P016383/1), National Centre for Atmospheric Science (NERC) (via University of Leeds) (R8/H12/83/003
New estimate of particulate emissions from Indonesian peat fires in 2015
Indonesia contains large areas of peatland that have been drained and cleared of natural vegetation, making them susceptible to burning. Peat fires emit considerable amounts of carbon dioxide, particulate matter (PM) and other trace gases, contributing to climate change and causing regional air pollution. However, emissions from peat fires are uncertain, due to uncertainties in emission factors and fuel consumption. We used the Weather Research and Forecasting model with chemistry and measurements of PM concentrations to constrain PM emissions from Indonesian fires during 2015, one of the largest fire seasons in recent decades.Published versio
Evaluation of tropospheric ozone and ozone precursors in simulations from the HTAPII and CCMI model intercomparisons – a focus on the Indian subcontinent
Here we present results from an evaluation of model simulations from the
International Hemispheric Transport of Air Pollution Phase II (HTAPII) and
Chemistry Climate Model Initiative (CCMI) model inter-comparison projects
against a comprehensive series of ground-based, aircraft and satellite
observations of ozone mixing ratios made at various locations across India.
The study focuses on the recent past (observations from 2008 to 2013, models
from 2009–2010) as this is most pertinent to understanding the health
impacts of ozone. To our understanding this is the most comprehensive
evaluation of these models' simulations of ozone across the Indian
subcontinent to date. This study highlights some significant successes and
challenges that the models face in representing the oxidative chemistry of
the region.
The multi-model range in area-weighted surface ozone over the Indian
subcontinent is 37.26–56.11 ppb, whilst the population-weighted range is
41.38–57.5 ppb. When compared against surface observations from the
Modelling Atmospheric Pollution and Networking (MAPAN) network of eight
semi-urban monitoring sites spread across India, we find that the models tend
to simulate higher ozone than that which is observed. However, observations
of NOx and CO tend to be much higher than modelled mixing
ratios, suggesting that the underlying emissions used in the models do not
characterise these regions accurately and/or that the resolution of the
models is not adequate to simulate the photo-chemical environment of these
surface observations. Empirical orthogonal function (EOF) analysis is used in
order to identify the extent to which the models agree with regards to the
spatio-temporal distribution of the tropospheric ozone column, derived using
OMI-MLS observations. We show that whilst the models agree with the spatial
pattern of the first EOF of observed tropospheric ozone column, most of the
models simulate a peak in the first EOF seasonal cycle represented by
principle component 1, which is later than the observed peak. This suggests a
widespread systematic bias in the timing of emissions or some other unknown
seasonal process.
In addition to evaluating modelled ozone mixing ratios, we explore modelled
emissions of NOx, CO, volatile organic compounds (VOCs) and the ozone response to the
emissions. We find a high degree of variation in emissions from
non-anthropogenic sources (e.g. lightning NOx and biomass
burning CO) between models. Total emissions of NOx and CO
over India vary more between different models in the same model intercomparison project (MIP) than the same
model used in different MIPs, making it impossible to diagnose whether
differences in modelled ozone are due to emissions or model processes. We
therefore recommend targeted experiments to pinpoint the exact causes of
discrepancies between modelled and observed ozone and ozone precursors for
this region. To this end, a higher density of long-term monitoring sites
measuring not only ozone but also ozone precursors including speciated VOCs,
located in more rural regions of the Indian subcontinent, would enable
improvements in assessing the biases in models run at the resolution found in
HTAPII and CCMI.</p
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