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

2014 ◽  
Vol 14 (1) ◽  
pp. 177-198 ◽  
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 ◽  
Chemical Transport Model ◽  
Ozone Monitoring Instrument ◽  
Intercontinental Transport ◽  
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. We consider a global chemical transport model (MOdèle de Chimie Atmosphérique à Grande Échelle, MOCAGE) in combination with a linear ozone chemistry scheme to examine the impact of assimilating observations from the Microwave Limb Sounder (MLS) and the Infrared Atmospheric Sounding Interferometer (IASI). The assimilation of the two instruments is performed by means of a variational algorithm (4D-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 ozonesonde measurements to verify the presence of observations and model biases. Furthermore, a longer analysis of 6 months (July–December 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). The assimilation of IASI tropospheric ozone observations (1000–225 hPa columns, TOC – tropospheric O3 column) decreases the RMSE of the model from 40 to 20% in the tropics (30° S–30° N), whereas it is not effective at higher latitudes. Results are confirmed by a comparison with additional ozone data sets 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 insensitive to the assimilation parameters. We conclude that the combination of a simplified ozone chemistry scheme with frequent satellite observations is a valuable tool for the long-term analysis of stratospheric and free-tropospheric ozone.

scholarly journals Modelling the optical and radiative properties of freshly emitted light absorbing carbon within an atmospheric chemical transport model

2009 ◽  
Vol 9 (6) ◽  
pp. 25443-25486 ◽  
Author(s):  
M. Kahnert
Keyword(s):  
Optical Properties ◽  
Electromagnetic Scattering ◽  
Radiative Forcing ◽  
Transport Model ◽  
Chemical Transport ◽  
Radiative Properties ◽  
Optical Observations ◽  
Chemical Transport Model ◽  
Aggregate Model ◽  
Approximate Methods

Abstract. Light absorbing carbon (LAC) aerosols have a complex, fractal-like aggregate structure. Their optical and radiative properties are notoriously difficult to model, and approximate methods may introduce large errors both in the interpretation of aerosol remote sensing observations, and in quantifying the direct radiative forcing effect of LAC. In this paper a method based on rigorous electromagnetic theory is employed for computing the optical properties of freshly emitted, externally mixed LAC aggregates. The computations are performed at wavelengths of 440 nm and 870 nm, and they cover the entire size range relevant for modelling these kinds of aerosols. The method for solving the electromagnetic scattering and absorption problem for aggregates proves to be sufficiently stable and fast to make accurate multiple-band computations of LAC optical properties feasible. The results from the electromagnetic computations are processed such that they can readily be integrated into a chemical transport model (CTM), which is a prerequisite for constructing robust observation operators for chemical data assimilation of aerosol optical observations. A case study is performed, in which results obtained with the coupled optics/CTM model are employed as input to detailed radiative transfer computations at a polluted European location. It is found that the still popular homogeneous sphere approximation significantly underestimates the radiative forcing at top of atmosphere as compared to the results obtained with the aggregate model. Notably, the LAC forcing effect predicted with the aggregate model is less than that one obtains by assuming a prescribed mass absorption coefficient for LAC.

scholarly journals Modelling the optical and radiative properties of freshly emitted light absorbing carbon within an atmospheric chemical transport model

2010 ◽  
Vol 10 (3) ◽  
pp. 1403-1416 ◽  
Author(s):  
M. Kahnert
Keyword(s):  
Optical Properties ◽  
Electromagnetic Scattering ◽  
Radiative Forcing ◽  
Transport Model ◽  
Chemical Transport ◽  
Radiative Properties ◽  
Optical Observations ◽  
Chemical Transport Model ◽  
Aggregate Model ◽  
Approximate Methods

Abstract. Light absorbing carbon (LAC) aerosols have a complex, fractal-like aggregate structure. Their optical and radiative properties are notoriously difficult to model, and approximate methods may introduce large errors both in the interpretation of aerosol remote sensing observations, and in quantifying the direct radiative forcing effect of LAC. In this paper a numerically exact method for solving Maxwell's equations is employed for computing the optical properties of freshly emitted, externally mixed LAC aggregates. The computations are performed at wavelengths of 440 nm and 870 nm, and they cover the entire size range relevant for modelling these kinds of aerosols. The method for solving the electromagnetic scattering and absorption problem for aggregates proves to be sufficiently stable and fast to make accurate multiple-band computations of LAC optical properties feasible. The results from the electromagnetic computations are processed such that they can readily be integrated into a chemical transport model (CTM), which is a prerequisite for constructing robust observation operators for chemical data assimilation of aerosol optical observations. A case study is performed, in which results obtained with the coupled optics/CTM model are employed as input to detailed radiative transfer computations at a polluted European location. It is found that the still popular homogeneous sphere approximation significantly underestimates the radiative forcing at top of atmosphere as compared to the results obtained with the aggregate model. Notably, the LAC forcing effect predicted with the aggregate model is less than that one obtains by assuming a prescribed mass absorption cross section for LAC.

scholarly journals Sensitivity Experiments of Direct Radiative Forcing Caused by Mineral Dust Simulated with a Chemical Transport Model

2005 ◽  
Vol 83A ◽  
pp. 315-331 ◽  
Author(s):  
Teruo AOKI ◽  
Taichu Y. TANAKA ◽  
Akihiro UCHIYAMA ◽  
Masaru CHIBA ◽  
Masao MIKAMI ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Transport Model ◽  
Mineral Dust ◽  
Chemical Transport ◽  
Chemical Transport Model ◽  
Sensitivity Experiments ◽  
Direct Radiative Forcing

scholarly journals Sudden changes in nitrogen dioxide emissions over Greece due to lockdown after the outbreak of COVID-19

2021 ◽  
Vol 21 (3) ◽  
pp. 1759-1774
Author(s):  
Maria-Elissavet Koukouli ◽  
Ioanna Skoulidou ◽  
Andreas Karavias ◽  
Isaak Parcharidis ◽  
Dimitris Balis ◽  
...  
Keyword(s):  
Air Quality ◽  
Nitrogen Dioxide ◽  
Transport Model ◽  
Chemical Transport ◽  
Capital City ◽  
Optical Absorption Spectroscopy ◽  
Chemical Transport Model ◽  
Ozone Monitoring Instrument ◽  
Transport Modelling ◽  
Monitoring Instrument

Abstract. The unprecedented order, in modern peaceful times, for a near-total lockdown of the Greek population as a means of protection against severe acute respiratory syndrome coronavirus 2, commonly known as COVID-19, has generated unintentional positive side-effects with respect to the country's air quality levels. Sentinel-5 Precursor/Tropospheric Monitoring Instrument (S5P/TROPOMI) monthly mean tropospheric nitrogen dioxide (NO2) observations show an average change of −34 % to +20 % and −39 % to −5 % with an average decrease of −15 % and −11 % for March and April 2020 respectively, compared with the previous year, over the six larger Greek metropolitan areas; this is mostly attributable to vehicular emission reductions. For the capital city of Athens, weekly analysis was statistically possible for the S5P/TROPOMI observations and revealed a marked decline in the NO2 load of between −8 % and −43 % for 7 of the 8 weeks studied; this is in agreement with the equivalent Ozone Monitoring Instrument (OMI)/Aura observations as well as the ground-based estimates of a multi-axis differential optical absorption spectroscopy ground-based instrument. Chemical transport modelling of the NO2 columns, provided by the Long Term Ozone Simulation European Operational Smog (LOTOS-EUROS) chemical transport model, shows that the magnitude of these reductions cannot solely be attributed to the difference in meteorological factors affecting NO2 levels during March and April 2020 and the equivalent time periods of the previous year. Taking this factor into account, the resulting decline was estimated to range between ∼ −25 % and −65 % for 5 of the 8 weeks studied, with the remaining 3 weeks showing a positive average of ∼ 10 %; this positive average was postulated to be due to the uncertainty of the methodology, which is based on differences. As a result this analysis, we conclude that the effect of the COVID-19 lockdown and the restriction of transport emissions over Greece is ∼ −10 %. As transport is the second largest sector (after industry) affecting Greece's air quality, this occasion may well help policymakers to enforce more targeted measures to aid Greece in further reducing emissions according to international air quality standards.

scholarly journals The UIUC three-dimensional stratospheric chemical transport model: Description and evaluation of the simulated source gases and ozone

1999 ◽  
Vol 104 (D9) ◽  
pp. 11755-11781 ◽  
Author(s):  
Eugene V. Rozanov ◽  
Vladimir A. Zubov ◽  
Michael E. Schlesinger ◽  
Fanglin Yang ◽  
Natalia G. Andronova
Keyword(s):  
Transport Model ◽  
Three Dimensional ◽  
Chemical Transport ◽  
Model Description ◽  
Chemical Transport Model ◽  
Simulated Source
Sign in / Sign up

Export Citation Format

Share Document