scholarly journals Aerosol-modulated heat stress in present and future climate of India

2021 ◽  
Author(s):  
Sagnik Dey ◽  
Rohit Kumar Choudhary ◽  
Abhishek Upadhayay ◽  
S. K. Dash
Keyword(s):  
Heat Stress ◽  
Radiative Forcing ◽  
Transport Model ◽  
Chemical Transport Model ◽  
Peninsular India ◽  
Climate Zones ◽  
Radiative Feedback ◽  
Emission Pathway ◽  
Aerosol Loading ◽  
Aerosol Emission

Abstract Heat stress is one of the leading natural causes of mortality in India. Aerosols can potentially impact heat stress by modulating the meteorological conditions via radiative feedback. However, a quantitative understanding of such impact is lacking. Here using a chemical transport model WRF-Chem, we showed that high aerosol loading in India was able to mask the heat stress (quantified by the Wet Bulb Globe Temperature, WBGT) by 0.3-1.5C in 2010 with a regional heterogeneity across the major climate zones in India. However, the cooling effect of aerosol direct radiative forcing is partially compensated by an increase in humidity. To understand the potential impact of air quality improvement (i.e., reducing aerosol load) on heat stress in the future, WBGT was projected for 2030 under two contrasting aerosol emission pathways. We found that the heat stress would increase by >0.75C in all the climate zones in India except in the montane zone under the RCP4.5 scenario with a bigger margin of increase in the mitigation emission pathway relative to the baseline emission pathway. On the contrary, under the RCP8.5 scenario, the heat stress is projected to increase in limited regions such as the tropical wet and dry, north-eastern part of the humid subtropical, tropical wet, and semi-arid climate zone in peninsular India. Our results demonstrate that aerosols modulate heat stress, and therefore, the heat stress projections in India and anywhere else with high aerosol loading should consider aerosol radiative feedback.

scholarly journals Key factors affecting single scattering albedo calculation: Implications for aerosol climate forcing

2017 ◽  
Author(s):  
Duseong S. Jo ◽  
Rokjin J. Park ◽  
Jaein I. Jeong ◽  
Gabriele Curci ◽  
Hyung-Min Lee ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Radiative Forcing ◽  
Transport Model ◽  
Geometric Mean ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Geometric Standard Deviation ◽  
Physical Parameters ◽  
Chemical Transport Model ◽  
Aerosol Mass

Abstract. Single Scattering Albedo (SSA), the ratio of scattering efficiency to total extinction efficiency, is an essential parameter used to estimate the Direct Radiative Forcing (DRF) of aerosols. However, SSA is one of the large contributors to the uncertainty of DRF estimations. In this study, we examined the sensitivity of SSA calculations to the physical properties of absorbing aerosols, in particular, Black Carbon (BC), Brown Carbon (BrC), and dust. We used GEOS-Chem 3-D global chemical transport model (CTM) simulations and a post-processing tool for the aerosol optical properties (FlexAOD). The model and input parameters were evaluated by comparison against the observed aerosol mass concentrations and the Aerosol Optical Depth (AOD) values obtained from global surface observation networks such as the global Aerosol Mass Spectrometer (AMS) dataset, the Surface Particulate Matter Network (SPARTAN), and the Aerosol Robotic Network (AERONET). The model was generally successful in reproducing the observed variability of both the Particulate Matter 2.5 μm (PM2.5) and AOD (R ~ 0.76) values, although it underestimated the magnitudes by approximately 20 %. Our sensitivity tests of the SSA calculation revealed that the aerosol physical parameters, which have generally received less attention than the aerosol mass loadings, can cause large uncertainties in the resulting DRF estimation. For example, large variations in the calculated BC absorption may result from slight changes of the geometric mean radius, geometric standard deviation, real and imaginary refractive indices, and density. The inclusion of BrC and observationally-constrained dust size distributions also significantly affected the SSA, and resulted in a remarkable improvement for the simulated SSA at 440 nm (bias was reduced by 44–49 %) compared with the AERONET observations. Based on the simulations performed during this study, we found that the global aerosol direct radiative effect was increased by 10 % after the SSA bias was reduced.

scholarly journals Concentrations and source regions of light absorbing impurities in snow/ice in northern Pakistan and their impact on snow albedo

2017 ◽  
Author(s):  
Chaman Gul ◽  
Siva Praveen Puppala ◽  
Shichang Kang ◽  
Bhupesh Adhikary ◽  
Yulan Zhang ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Transport Model ◽  
Chemical Transport ◽  
Small Contribution ◽  
Northern Pakistan ◽  
Chemical Transport Model ◽  
Transport Modelling ◽  
Snow Albedo ◽  
Source Regions ◽  
Snow And Ice

Abstract. Black carbon (BC), water-insoluble organic carbon (OC), and mineral dust are important particulate impurities in snow and ice, which significantly reduce albedo and accelerate melting. Surface snow and ice samples were collected from the Karakoram–Himalayan region of northern Pakistan during 2015 and 2016 in summer (six glaciers), autumn (two glaciers), and winter (six mountain valleys). The average BC concentration overall was 2130 ± 1560 ngg−1 in summer samples, 2883 ± 3439 ngg−1 in autumn samples, and 992 ± 883 ngg−1 in winter samples. The average water insoluble OC concentration overall was 1839 ± 1108 ngg−1 in summer samples, 1423 ± 208 ngg−1 in autumn samples, and 1342 ± 672 ngg−1 in winter samples. The overall concentration of BC, OC, and dust in aged snow samples collected during the summer campaign was higher than the concentration in ice samples. The values are relatively high compared to reports by others for the Himalayas and Tibetan Plateau. This is probably the result of taking more representative samples at lower elevation where deposition is higher and the effects of ageing and enrichment more marked. A reduction in snow albedo of 0.1–8.3 % for fresh snow and 0.9–32.5 % for aged snow was calculated for selected solar zenith angles during day time using the Snow, Ice, and Aerosol Radiation (SNICAR) model. Daily mean albedo was reduced by 0.07–12.0 %. The calculated radiative forcing ranged from 0.16 to 43.45 Wm−2 depending on snow type, solar zenith angle, and location. The potential source regions of the deposited pollutants were identified using spatial variance in wind vector maps, emission inventories coupled with backward air trajectories, and simple region tagged chemical transport modelling. Central, South, and West Asia were the major sources of pollutants during the sampling months, with only a small contribution from East Asia. Analysis based on the Weather Research and Forecasting (WRF-STEM) chemical transport model identified a significant contribution (more than 70 %) from South Asia at selected sites. Research into the presence and effect of pollutants in the glaciated areas of Pakistan is economically significant because the surface water resources in the country mainly depend on the rivers (the Indus and its tributaries) that flow from this glaciated area.

scholarly journals Contrasting the direct radiative effect and direct radiative forcing of aerosols

2014 ◽  
Vol 14 (11) ◽  
pp. 5513-5527 ◽  
Author(s):  
C. L. Heald ◽  
D. A. Ridley ◽  
J. H. Kroll ◽  
S. R. H. Barrett ◽  
K. E. Cady-Pereira ◽  
...  
Keyword(s):  
Energy Balance ◽  
Radiative Forcing ◽  
Transport Model ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Radiative Effect ◽  
Chemical Transport Model ◽  
Anthropogenic Aerosols ◽  
Anthropogenic Aerosol ◽  
Direct Radiative Forcing

Abstract. The direct radiative effect (DRE) of aerosols, which is the instantaneous radiative impact of all atmospheric particles on the Earth's energy balance, is sometimes confused with the direct radiative forcing (DRF), which is the change in DRE from pre-industrial to present-day (not including climate feedbacks). In this study we couple a global chemical transport model (GEOS-Chem) with a radiative transfer model (RRTMG) to contrast these concepts. We estimate a global mean all-sky aerosol DRF of −0.36 Wm−2 and a DRE of −1.83 Wm−2 for 2010. Therefore, natural sources of aerosol (here including fire) affect the global energy balance over four times more than do present-day anthropogenic aerosols. If global anthropogenic emissions of aerosols and their precursors continue to decline as projected in recent scenarios due to effective pollution emission controls, the DRF will shrink (−0.22 Wm−2 for 2100). Secondary metrics, like DRE, that quantify temporal changes in both natural and anthropogenic aerosol burdens are therefore needed to quantify the total effect of aerosols on climate.

scholarly journals Combined assimilation of IASI and MLS observations to constrain tropospheric and stratospheric ozone in a global chemical transport model

2013 ◽  
Vol 13 (8) ◽  
pp. 21455-21505
Author(s):  
E. Emili ◽  
B. Barret ◽  
S. Massart ◽  
E. Le Flochmoen ◽  
A. Piacentini ◽  
...  
Keyword(s):  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Transport Model ◽  
Stratospheric Ozone ◽  
Chemical Transport ◽  
Free Troposphere ◽  
Chemical Transport Model ◽  
Ozone Monitoring Instrument ◽  
Global Chemical Transport Model ◽  
The Impact

Abstract. Accurate and temporally resolved fields of free-troposphere ozone are of major importance to quantify the intercontinental transport of pollution and the ozone radiative forcing. In this study we examine the impact of assimilating ozone observations from the Microwave Limb Sounder (MLS) and the Infrared Atmospheric Sounding Interferometer (IASI) in a global chemical transport model (MOdèle de Chimie Atmosphérique à Grande Échelle, MOCAGE). The assimilation of the two instruments is performed by means of a variational algorithm (4-D-VAR) and allows to constrain stratospheric and tropospheric ozone simultaneously. The analysis is first computed for the months of August and November 2008 and validated against ozone-sondes measurements to verify the presence of observations and model biases. It is found that the IASI Tropospheric Ozone Column (TOC, 1000–225 hPa) should be bias-corrected prior to assimilation and MLS lowermost level (215 hPa) excluded from the analysis. Furthermore, a longer analysis of 6 months (July–August 2008) showed that the combined assimilation of MLS and IASI is able to globally reduce the uncertainty (Root Mean Square Error, RMSE) of the modeled ozone columns from 30% to 15% in the Upper-Troposphere/Lower-Stratosphere (UTLS, 70–225 hPa) and from 25% to 20% in the free troposphere. The positive effect of assimilating IASI tropospheric observations is very significant at low latitudes (30° S–30° N), whereas it is not demonstrated at higher latitudes. Results are confirmed by a comparison with additional ozone datasets like the Measurements of OZone and wAter vapour by aIrbus in-service airCraft (MOZAIC) data, the Ozone Monitoring Instrument (OMI) total ozone columns and several high-altitude surface measurements. Finally, the analysis is found to be little sensitive to the assimilation parameters and the model chemical scheme, due to the high frequency of satellite observations compared to the average life-time of free-troposphere/low-stratosphere ozone.

scholarly journals Radiative forcing and climate metrics for ozone precursor emissions: the impact of multi-model averaging

2014 ◽  
Vol 14 (19) ◽  
pp. 27195-27231
Author(s):  
C. R. MacIntosh ◽  
K. P. Shine ◽  
W. J. Collins
Keyword(s):  
Radiative Forcing ◽  
Transport Model ◽  
Task Force ◽  
Mean Field ◽  
Model Averaging ◽  
Chemical Transport Model ◽  
Ensemble Mean ◽  
The Mean ◽  
The Individual ◽  
The Impact

Abstract. Multi-model ensembles are frequently used to assess understanding of the response of ozone and methane lifetime to changes in emissions of ozone precursors such as NOx, VOC and CO. When these ozone changes are used to calculate radiative forcing (RF) (and climate metrics such as the global warming potential (GWP) and global temperature potential (GTP)) there is a methodological choice, determined partly by the available computing resources, as to whether the mean ozone (and methane lifetime) changes are input to the radiation code, or whether each model's ozone and methane changes are used as input, with the average RF computed from the individual model RFs. We use data from the Task Force on Hemispheric Transport of Air Pollution Source-Receptor global chemical transport model ensemble to assess the impact of this choice for emission changes in 4 regions (East Asia, Europe, North America and South Asia). We conclude that using the multi-model mean ozone and methane responses is accurate for calculating the mean RF, with differences up to 0.6% for CO, 0.7% for VOC and 2% for NOx. Differences of up to 60% for NOx 7% for VOC and 3% for CO are introduced into the 20 year GWP as a result of the exponential decay terms, with similar values for the 20 years GTP. However, estimates of the SD calculated from the ensemble-mean input fields (where the SD at each point on the model grid is added to or subtracted from the mean field) are almost always substantially larger in RF, GWP and GTP metrics than the true SD, and can be larger than the model range for short-lived ozone RF, and for the 20 and 100 year GWP and 100 year GTP. We find that the effect is generally most marked for the case of NOx emissions, where the net effect is a smaller residual of terms of opposing signs. For example, the SD for the 20 year GWP is two to three times larger using the ensemble-mean fields than using the individual models to calculate the RF. Hence, while the average of multi-model fields are appropriate for calculating mean RF, GWP and GTP, they are not a reliable method for calculating the uncertainty in these fields, and in general overestimate the uncertainty.

scholarly journals Concentrations and source regions of light-absorbing particles in snow/ice in northern Pakistan and their impact on snow albedo

2018 ◽  
Vol 18 (7) ◽  
pp. 4981-5000 ◽  
Author(s):  
Chaman Gul ◽  
Siva Praveen Puppala ◽  
Shichang Kang ◽  
Bhupesh Adhikary ◽  
Yulan Zhang ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Transport Model ◽  
Chemical Transport ◽  
The Tibetan Plateau ◽  
Small Contribution ◽  
Northern Pakistan ◽  
Chemical Transport Model ◽  
Snow Albedo ◽  
Source Regions ◽  
Snow And Ice

Abstract. Black carbon (BC), water-insoluble organic carbon (OC), and mineral dust are important particles in snow and ice which significantly reduce albedo and accelerate melting. Surface snow and ice samples were collected from the Karakoram–Himalayan region of northern Pakistan during 2015 and 2016 in summer (six glaciers), autumn (two glaciers), and winter (six mountain valleys). The average BC concentration overall was 2130 ± 1560 ng g−1 in summer samples, 2883 ± 3439 ng g−1 in autumn samples, and 992 ± 883 ng g−1 in winter samples. The average water-insoluble OC concentration overall was 1839 ± 1108 ng g−1 in summer samples, 1423 ± 208 ng g−1 in autumn samples, and 1342 ± 672 ng g−1 in winter samples. The overall concentration of BC, OC, and dust in aged snow samples collected during the summer campaign was higher than the concentration in ice samples. The values are relatively high compared to reports by others for the Himalayas and the Tibetan Plateau. This is probably the result of taking more representative samples at lower elevation where deposition is higher and the effects of ageing and enrichment are more marked. A reduction in snow albedo of 0.1–8.3 % for fresh snow and 0.9–32.5 % for aged snow was calculated for selected solar zenith angles during daytime using the Snow, Ice, and Aerosol Radiation (SNICAR) model. The daily mean albedo was reduced by 0.07–12.0 %. The calculated radiative forcing ranged from 0.16 to 43.45 W m−2 depending on snow type, solar zenith angle, and location. The potential source regions of the deposited pollutants were identified using spatial variance in wind vector maps, emission inventories coupled with backward air trajectories, and simple region-tagged chemical transport modeling. Central, south, and west Asia were the major sources of pollutants during the sampling months, with only a small contribution from east Asia. Analysis based on the Weather Research and Forecasting (WRF-STEM) chemical transport model identified a significant contribution (more than 70 %) from south Asia at selected sites. Research into the presence and effect of pollutants in the glaciated areas of Pakistan is economically significant because the surface water resources in the country mainly depend on the rivers (the Indus and its tributaries) that flow from this glaciated area.

scholarly journals Impact of aircraft NO<sub>x</sub> emissions on the atmosphere – tradeoffs to reduce the impact

2005 ◽  
Vol 5 (6) ◽  
pp. 12255-12311 ◽  
Author(s):  
M. Gauss ◽  
I. S. A. Isaksen ◽  
D. S. Lee ◽  
O. A. Søvde
Keyword(s):  
Radiative Forcing ◽  
Lower Stratosphere ◽  
Transport Model ◽  
Reactive Nitrogen ◽  
Chemical Transport Model ◽  
Reference Case ◽  
Northern Latitudes ◽  
Tropopause Region ◽  
Eu Project ◽  
The Impact

Abstract. Within the EU-project TRADEOFF, the impact of NOx (=NO+NO2) emissions from subsonic aviation upon the chemical composition of the atmosphere has been calculated with focus on changes in reactive nitrogen, ozone, and the chemical lifetime of methane. We apply a 3-D chemical transport model that includes comprehensive chemistry for both the troposphere and the stratosphere and uses various aircraft emission scenarios developed during TRADEOFF for the year 2000. The environmental effects of enhanced air traffic along polar routes and of possible changes in cruising altitude are investigated. In the reference case the model predicts aircraft-induced maximum increases of zonal-mean NOy (=total reactive nitrogen) between 156 pptv (August) and 322 pptv (May) in the tropopause region of the Northern Hemisphere. Resulting maximum increases in zonal-mean ozone vary between 3.1 ppbv in September and 7.7 ppbv in June. The lifetime of methane is calculated to decrease by 0.71%, inducing a radiative forcing of −6.4 mW/m2. Enhanced use of polar routes implies significantly larger zonal-mean ozone increases in high Northern latitudes during summer, while the effect is negligible in winter. Lowering the flight altitude leads to smaller ozone increase in the lower stratosphere and upper troposphere, and to larger ozone increase at lower altitudes. Regarding total ozone change, the degree of cancellation between these two effects depends on latitude and season, but annually and globally averaged the stratospheric decrease dominates, mainly due to washout of NOy in the troposphere, which weakens the tropospheric increase. Raising flight altitudes increases the ozone burden both in the troposphere and the lower stratosphere, primarily due to a more efficient accumulation of pollutants in the stratosphere.

scholarly journals Air quality and radiative forcing impacts of anthropogenic volatile organic compound emissions from ten world regions

2013 ◽  
Vol 13 (8) ◽  
pp. 21125-21157 ◽  
Author(s):  
M. M. Fry ◽  
M. D. Schwarzkopf ◽  
Z. Adelman ◽  
J. J. West
Keyword(s):  
Air Quality ◽  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Transport Model ◽  
Surface Ozone ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Chemical Transport Model ◽  
Large Variability ◽  
Volatile Organic

Abstract. Non-methane volatile organic compounds (NMVOCs) influence air quality and global climate change through their effects on secondary air pollutants and climate forcers. Here we simulate the air quality and radiative forcing (RF) impacts of changes in ozone, methane, and sulfate from halving anthropogenic NMVOC emissions globally and from 10 regions individually, using a global chemical transport model and a standalone radiative transfer model. Halving global NMVOC emissions decreases global annual average tropospheric methane and ozone by 36.6 ppbv and 3.3 Tg, respectively, and surface ozone by 0.67 ppbv. All regional reductions slow the production of PAN, resulting in regional to intercontinental PAN decreases and regional NOx increases. These NOx increases drive tropospheric ozone increases nearby or downwind of source regions in the Southern Hemisphere (South America, Southeast Asia, Africa, and Australia). Some regions' NMVOC emissions contribute importantly to air pollution in other regions, such as East Asia, Middle East, and Europe, whose impact on US surface ozone is 43%, 34%, and 34% of North America's impact. Global and regional NMVOC reductions produce widespread negative net RFs (cooling) across both hemispheres from tropospheric ozone and methane decreases, and regional warming and cooling from changes in tropospheric ozone and sulfate (via several oxidation pathways). The total global net RF for NMVOCs is estimated as 0.0277 W m−2 (~1.8% of CO2 RF since the preindustrial). The 100 yr and 20 yr global warming potentials (GWP100, GWP20) are 2.36 and 5.83 for the global reduction, and 0.079 to 6.05 and −1.13 to 18.9 among the 10 regions. The NMVOC RF and GWP estimates are generally lower than previously modeled estimates, due to differences among models in ozone, methane, and sulfate sensitivities, and the climate forcings included in each estimate. Accounting for a~fuller set of RF contributions may change the relative magnitude of each region's impacts. The large variability in the RF and GWP of NMVOCs among regions suggest that regionally-specific metrics may be necessary to include NMVOCs in multi-gas climate trading schemes.

scholarly journals The climate impact of ship NO<sub>x</sub> emissions: an improved estimate accounting for plume chemistry

2014 ◽  
Vol 14 (3) ◽  
pp. 3427-3458
Author(s):  
C. D. Holmes ◽  
M. J. Prather ◽  
G. C. M. Vinken
Keyword(s):  
Radiative Forcing ◽  
Transport Model ◽  
Parametric Representation ◽  
Climate Impact ◽  
Nox Emissions ◽  
Chemical Transport Model ◽  
Rf Components ◽  
Maritime Shipping ◽  
Sensitivity Tests ◽  
Emission Changes

Abstract. Nitrogen oxide (NOx) emissions from maritime shipping produce ozone (O3) and hydroxyl radicals (OH), which in turn destroy methane (CH4). The balance between this warming (due to O3) and cooling (due to CH4) determines the net effect of ship NOx on climate. Previous estimates of the chemical impact and radiative forcing (RF) of ship NOx have generally assumed that plumes of ship exhaust are instantly diluted into model grid cells spanning hundreds of kilometers, even though this is known to produce biased results. Here we improve the parametric representation of exhaust-gas chemistry developed in the GEOS-Chem chemical transport model (CTM) to provide the first estimate of RF from shipping that accounts for sub-grid-scale ship plume chemistry. The CTM now calculates O3 production and CH4 loss both within and outside the exhaust plumes and also accounts for the effect of wind speed. With the improved modeling of plumes, ship NOx perturbations are smaller than suggested by the ensemble of past global modeling studies, but if we assume instant dilution of ship NOx on the grid scale, the CTM reproduces previous model results. Our best estimates of the RF components from increasing ship NOx emissions by 1 Tg(N) yr−1 are smaller than given in the past literature: +3.4 ± 0.85 mW m−2 from the short-lived ozone increase, −5.0 ± 1.1 mW m−2 from the CH4 decrease, and −1.7 ± 0.7 mW m−2 from the long-lived O3 decrease that accompanies the CH4 change. The resulting net RF is −3.3 ± 1.8 mW m−2 for emissions of 1 Tg(N) yr−1. Due to non-linearity in O3 production as a function of background NOx, RF from large changes in ship NOx emissions, such as the increase since preindustrial times, is about 20% larger than this RF value for small marginal emission changes. Using sensitivity tests in one CTM, we quantify sources of uncertainty in the RF components and causes of the ±30% spread in past model results. The main source of uncertainty is the composition of the background atmosphere in the CTM, which is driven by model formulation (±10 to 20%) and the plausible range of anthropogenic emissions (±10%).

Exploring ice core sea ice proxies through process-based modelling

2021 ◽  
Author(s):  
Rachael Rhodes ◽  
Xin Yang ◽  
Eric Wolff
Keyword(s):  
Sea Ice ◽  
Atmospheric Chemistry ◽  
Transport Model ◽  
Ice Core ◽  
Ice Cores ◽  
Internal Variability ◽  
Atmospheric Composition ◽  
Chemical Transport Model ◽  
Aerosol Emission ◽  
Abrupt Shifts

&lt;p&gt;It is important to understand the magnitude and rate of past sea ice changes, as well as their timing relative to abrupt shifts in other components of Earth&amp;#8217;s climate system. Furthermore, records of past sea ice over the last few centuries are urgently needed to assess the scale of natural (internal) variability over decadal timescales. By continuously recording past atmospheric composition, polar ice cores have the potential to document changing sea ice conditions if atmospheric chemistry is altered.&amp;#160; Sea salt aerosol, specifically sodium (Na), and bromine enrichment (Br&lt;sub&gt;enr&lt;/sub&gt;, Br/Na enriched relative to seawater ratio) are two ice core sea ice proxies suggested following this premise.&lt;/p&gt;&lt;p&gt;Here we aim to move beyond a conceptual understanding of the controls on Na and Br&lt;sub&gt;enr&lt;/sub&gt; in ice cores by using process-based modelling to test hypotheses. We present results of experiments using a 3D global chemical transport model (p-TOMCAT) that represents marine aerosol emission, transport and deposition. Critically, the complex atmospheric chemistry of bromine is also included allowing us to explore the partitioning of Br between gas and aerosol phases. &amp;#160;&lt;/p&gt;

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