Anthropogenic water depletion in the Indo-Gangetic Plain

2020 ◽  
Author(s):  
Bingshi Liu ◽  
Xiancai Zou ◽  
Jiancheng Li
Keyword(s):  
Global Climate ◽  
Monsoon Season ◽  
Supply And Demand ◽  
Gangetic Plain ◽  
Water Depletion ◽  
Continental Scale ◽  
Glacier Meltwater ◽  
Terrestrial Water ◽  
Indo Gangetic Plain ◽  
Precipitation And Temperature

<p>The Indo-Gangetic Plain, feeding more than 9 billion people, are facing serious water scarcity due to expanding populations and development in agriculture and industry. Rainfall concentrated in monsoon season, about 70% of precipitation falls between June and September, causes the imbalance between water supply and demand. A large amount of groundwater is extracted for irrigation during dry season, causes the groundwater to decline. Increasing glacier meltwater under the ongoing warming of global climate from upstream high mountainous also modulates the variation of terrestrial water storage (TWS) in this region. Thus, estimating and evaluating anthropogenic water depletion are beneficial to water resources protection and management in the Indo-Gangetic Plain.</p><p>Here, we propose a method to remove the influence of climate variability and obtain human-driven TWS variability. Atmosphere-driven TWS variability is estimated by a relationship between change in TWS (GRACE data) and precipitation and temperature, which has been confirmed that these two variables (precipitation and temperature) already explain a substantial fraction of continental-scale run off dynamics in previous studies. Glacier melting recharge from upstream high mountainous is calculated by the proportion with the temperature.</p><p>Results show that the rate of anthropogenic depletion of water in Indus Plain increased from -5.5 km<sup>3</sup>/yr to -25.0 km<sup>3</sup>/yr during 2003 - 2011 due to the deficient precipitation, and remained stable from 2011 to 2016 at the rate of ~-26.0 km<sup>3</sup>/yr with increasing precipitation and enhancing glacier meltwater recharge. The rate of anthropogenic depletion of water in Ganges Plain (including the Brahmaputra River) slowed from -37.7 km<sup>3</sup>/yr to -12.0 km<sup>3</sup>/yr during 2003 -2011due to the increased glacier meltwater recharge, which reduced the pressure of irrigation water in northwest of the Plain. However, with the increasing temperature since 2014, The rate of anthropogenic depletion of water increased to -20.0 km<sup>3</sup>/yr in 2016.</p>

On the frequency of the 2015 monsoon season drought in the Indo-Gangetic Plain

2016 ◽  
Vol 43 (23) ◽  
pp. 12,102-12,112 ◽  
Author(s):  
Vimal Mishra ◽  
Saran Aadhar ◽  
Akarsh Asoka ◽  
Sivananda Pai ◽  
Rohini Kumar
Keyword(s):  
Monsoon Season ◽  
Gangetic Plain ◽  
Indo Gangetic Plain

scholarly journals Importance of snow and glacier meltwater for agriculture on the Indo-Gangetic Plain

2019 ◽  
Vol 2 (7) ◽  
pp. 594-601 ◽  
Author(s):  
H. Biemans ◽  
C. Siderius ◽  
A. F. Lutz ◽  
S. Nepal ◽  
B. Ahmad ◽  
...  
Keyword(s):  
Gangetic Plain ◽  
Glacier Meltwater ◽  
Indo Gangetic Plain

scholarly journals Which processes drive observed variations of HCHO columns over India?

2018 ◽  
Vol 18 (7) ◽  
pp. 4549-4566 ◽  
Author(s):  
Luke Surl ◽  
Paul I. Palmer ◽  
Gonzalo González Abad
Keyword(s):  
Atmospheric Chemistry ◽  
Seasonal Cycle ◽  
Transport Model ◽  
Monsoon Season ◽  
Gangetic Plain ◽  
Model Calculations ◽  
Propene Oxidation ◽  
Meridional Gradient ◽  
Northeastern India ◽  
Continental Scale

Abstract. We interpret HCHO column variations observed by the Ozone Monitoring Instrument (OMI), aboard the NASA Aura satellite, over India during 2014 using the GEOS-Chem atmospheric chemistry and transport model. We use a nested version of the model with a horizontal resolution of approximately 25 km. HCHO columns are related to local emissions of volatile organic compounds (VOCs) with a spatial smearing that increases with the VOC lifetime. Over India, HCHO has biogenic, pyrogenic, and anthropogenic VOC sources. Using a 0-D photochemistry model, we find that isoprene has the largest molar yield of HCHO which is typically realized within a few hours. We also find that forested regions that neighbour major urban conurbations are exposed to high levels of nitrogen oxides. This results in depleted hydroxyl radical concentrations and a delay in the production of HCHO from isoprene oxidation. We find that propene is the only anthropogenic VOC emitted in major Indian cities that produces HCHO at a comparable (but slower) rate to isoprene. The GEOS-Chem model reproduces the broad-scale annual mean HCHO column distribution observed by OMI (r = 0.6), which is dominated by a distinctive meridional gradient in the northern half of the country, and by localized regions of high columns that coincide with forests. Major discrepancies are noted over the Indo-Gangetic Plain (IGP) and Delhi. We find that the model has more skill at reproducing observations during winter (JF) and pre-monsoon (MAM) months with Pearson correlations r > 0.5 but with a positive model bias of  ≃ 1×1015 molec cm−2. During the monsoon season (JJAS) we reproduce only a diffuse version of the observed meridional gradient (r = 0.4). We find that on a continental scale most of the HCHO column seasonal cycle is explained by monthly variations in surface temperature (r = 0.9), suggesting a role for biogenic VOCs, in agreement with the 0-D and GEOS-Chem model calculations. We also find that the seasonal cycle during 2014 is not significantly different from the 2008 to 2015 mean seasonal variation. There are two main loci for biomass burning (the states of Punjab and Haryana, and northeastern India), which we find makes a significant contribution (up to 1×1015 molec cm−2) to observed HCHO columns only during March and April over northeastern India. The slow production of HCHO from propene oxidation results in a smeared hotspot over Delhi that we resolve only on an annual mean timescale by using a temporal oversampling method. Using a linear regression model to relate GEOS-Chem isoprene emissions to HCHO columns we infer seasonal isoprene emissions over two key forest regions from the OMI HCHO column data. We find that the a posteriori emissions are typically lower than the a priori emissions, with a much stronger reduction of emissions during the monsoon season. We find that this reduction in emissions during monsoon months coincides with a large drop in satellite observations of leaf phenology that recovers in post monsoon months. This may signal a forest-scale response to monsoon conditions.

scholarly journals Which processes drive observed variations of HCHO columns over India?

2017 ◽  
Author(s):  
Luke Surl ◽  
Paul I. Palmer ◽  
Gonzalo González Abad
Keyword(s):  
Atmospheric Chemistry ◽  
Seasonal Cycle ◽  
Transport Model ◽  
Monsoon Season ◽  
Gangetic Plain ◽  
Model Calculations ◽  
Propene Oxidation ◽  
Meridional Gradient ◽  
Northeastern India ◽  
Continental Scale

Abstract. We interpret HCHO column variations observed by the Ozone Monitoring Instrument (OMI), aboard the NASA Aura satellite, over India during 2014 using the GEOS-Chem atmospheric chemistry and transport model. We use a nested version of the model with a spatial resolution of approximately 25 km. HCHO columns are related to local emissions of volatile organic compounds (VOCs) with a spatial smearing that increases with the VOC lifetime. Over India, HCHO has biogenic, pyrogenic, and anthropogenic VOC sources. Using a 0-D photochemistry model, we find that isoprene has the largest molar yield of HCHO that is typically realized within a few hours. We find that forested regions that neighbours major urban conurbations are exposed to high levels of nitrogen oxides. This results in depleted hydroxyl radical concentrations and a delay in the production of HCHO from isoprene oxidation. We find that propene is the only anthropogenic VOC emitted in major Indian cities that produces HCHO at a comparable (slower) rate to isoprene. The GEOS-Chem model reproduces the broadscale annual mean HCHO column distribution observed by OMI (r = 0.6), which is dominated by a distinctive meridional gradient in the northern half of the country, and by localized regions of high columns that coincide with forests. Major discrepancies are over the Indo-Gangetic Plain and Delhi. We find that the model has more skill at reproducing observations during winter (JF) and pre-monsoon (MAM) months with Pearson correlations r > 0.5 but with a positive model bias of 1 × 1015 molec/cm2. During the monsoon season (JJAS) we reproduce only a diffuse version of the observed meridional gradient (r = 0.4). Generally, we find that on a continental scale most of the seasonal cycle is explained by monthly variations in surface temperature (r = 0.9), suggesting a strong role for biogenic VOCs, in agreement with the 0-D and GEOS-Chem model calculations. We also find that the seasonal cycle during 2014 is not significantly different from the 2008–2015 mean seasonal variation but there are large year to year variations. There are two main loci for biomass burning (states of Punjab and Haryana, and northeastern India), which we find only contributes a significant contribution (up to 1 × 1015 molec/cm2) to observed HCHO columns during March to April over northeastern India. The slow production of HCHO from propene oxidation results in a smeared hotspot over Delhi that we resolve only on an annual mean timescale by using a temporal oversampling method. Using a linear regression model to relate GEOS-Chem isoprene emissions to HCHO columns we infer seasonal isoprene emissions over two key forest regions from the OMI HCHO column data. We find that the a posteriori emissions are typically lower than the a priori emissions, with a much stronger reduction of emissions during the monsoon season. We find that this reduction in emissions during monsoon months coincides with a large drop in satellite observations of leaf phenology that recovers in post monsoon months. This may signal a forest-scale response to monsoon conditions.

scholarly journals Vertical and horizontal distribution of sub-micron aerosol chemical composition and physical characteristics across Northern India, during the pre-monsoon and monsoon seasons

2018 ◽  
pp. 1-31
Author(s):  
James Brooks ◽  
James D. Allan ◽  
Paul I. Williams ◽  
Dantong Liu ◽  
Cathryn Fox ◽  
...  
Keyword(s):  
Black Carbon ◽  
Total Mass ◽  
Mass Concentration ◽  
Monsoon Season ◽  
Aerosol Layer ◽  
Gangetic Plain ◽  
Submicron Aerosol ◽  
Aerosol Mass ◽  
Indo Gangetic Plain ◽  
Mass Concentrations

<p><strong>Abstract.</strong> The vertical distribution in the physical and chemical properties of submicron aerosol has been characterised across northern India for the first time using airborne in-situ measurements. This study focusses primarily on the Indo-Gangetic Plain, a low-lying area in the north of India which commonly experiences high aerosol mass concentrations prior to the monsoon season. Data presented are from the UK Facility for Airborne Atmospheric Measurements BAe-146 research aircraft that performed flights in the region during the 2016 pre-monsoon (11<sup>th</sup> and 12<sup>th</sup> June) and monsoon (30<sup>th</sup> June to 11<sup>th</sup> July) seasons.</p> <p> Inside the Indo-Gangetic Plain boundary layer, organic matter dominated the submicron aerosol mass (43&amp;thinsp;%) followed by sulphate (29&amp;thinsp;%), ammonium (14&amp;thinsp;%), nitrate (7&amp;thinsp;%) and black carbon (7&amp;thinsp;%). However, outside the Indo-Gangetic Plain, sulphate was the dominant species contributing 44&amp;thinsp;% to the total submicron aerosol mass in the boundary layer, followed by organic matter (30&amp;thinsp;%), ammonium (14&amp;thinsp;%), nitrate (6&amp;thinsp;%) and black carbon (6&amp;thinsp;%). Chlorine mass concentrations were negligible throughout the campaign. Black carbon mass concentrations were higher inside the Indo-Gangetic Plain (2&amp;thinsp;µg/m<sup>3</sup> std) compared to outside (1&amp;thinsp;µg/m<sup>3</sup> std). Nitrate appeared to be controlled by thermodynamic processes, with increased mass concentration in conditions of lower temperature and higher relative humidity. Increased mass and number concentrations were observed inside the Indo-Gangetic Plain and the aerosol was more absorbing in this region, whereas outside the Indo-Gangetic Plain the aerosol was larger in size and more scattering in nature, suggesting greater dust presence especially in northwest India. The aerosol composition remained largely similar as the monsoon season progressed, but the total aerosol mass concentrations decreased by ~&amp;thinsp;50&amp;thinsp;% as the rainfall arrived; the pre-monsoon average total mass concentration was 30&amp;thinsp;µg/m<sup>3</sup> std compared to a monsoon average total mass concentration of 10&amp;ndash;20&amp;thinsp;µg/m<sup>3</sup> std. However, this mass concentration decrease was less noteworthy (~&amp;thinsp;20&amp;ndash;30&amp;thinsp;%) over the Indo-Gangetic Plain, likely due to the strength of emission sources in this region. Decreases occurred in coarse mode aerosol, with the fine mode fraction increasing with monsoon arrival. In the aerosol vertical profile, inside the Indo-Gangetic Plain during the pre-monsoon, organic aerosol and absorbing aerosol species dominated in the lower atmosphere (<&amp;thinsp;1.5&amp;thinsp;km) with sulphate, dust and other scattering aerosol species enhanced in an elevated aerosol layer above 1.5&amp;thinsp;km with maximum aerosol height ~&amp;thinsp;6&amp;thinsp;km. As the monsoon progressed into this region, the elevated aerosol layer diminished, the aerosol maximum height reduced to ~&amp;thinsp;2&amp;thinsp;km and the total mass concentrations decreased by ~&amp;thinsp;50&amp;thinsp;%. The dust and sulphate-dominated aerosol layer aloft was removed upon monsoon arrival, highlighted by an increase in fine mode fraction throughout the profile.</p>

scholarly journals Organic molecular tracers in the atmospheric aerosols from Lumbini, Nepal, in the northern Indo-Gangetic Plain: Influence of biomass burning

2017 ◽  
Author(s):  
Xin Wan ◽  
Shichang Kang ◽  
Quanlian Li ◽  
Dipesh Rupakheti ◽  
Qianggong Zhang ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Vanillic Acid ◽  
Monsoon Season ◽  
Syringic Acid ◽  
Rural Site ◽  
Aerosol Composition ◽  
Gangetic Plain ◽  
Post Monsoon ◽  
Post Monsoon Season ◽  
Indo Gangetic Plain

Abstract. To better understand the characteristics of biomass burning in the northern Indo-Gangetic Plain (IGP), total suspended particles were collected in a rural site, Lumbini, Nepal during April 2013 to March 2014 and analyzed for the biomass burning tracers (i.e., levoglucosan, mannosan, vanillic acid, etc.). The annual average concentration of levoglucosan was 734 ± 1043 ng m−3 with the maximum seasonal mean concentration during post-monsoon season (2206 ± 1753 ng m−3), followed by winter (1161 ± 1347 ng m−3), pre-monsoon (771 ± 524 ng m−3) and minimum concentration during monsoon season (212 ± 279 ng m−3). The other biomass burning tracers (mannosan, galactosan, p-hydroxybenzoic acid, vanillic acid, syringic acid, and dehydroabietic acid) also showed the similar seasonal variations. There were good correlations among levoglucosan, organic carbon (OC) and elemental carbon (EC), indicating significant impact of biomass burning activities on carbonaceous aerosol loading throughout the year in Lumbini area. According to the characteristic ratios: levoglucosan / mannosan (Lev / Man) and syringic acid / vanillic acid (Syr / Van), we deduced that the high abundances of biomass burning products during non-monsoon seasons were mainly caused by the burning of crop residues and hardwood while the softwood had less contribution. Based on the diagnostic tracer ratio (i.e., Lev / OC), the OC derived from biomass burning constituted large fraction of total OC, especially during post-monsoon season. By analyzing the MODIS fire spot product and five-day air-mass back trajectories, we further demonstrated that organic aerosol composition was not only related to the local agricultural activities and residential biomass usage, but was also impacted by the regional emissions. During the post-monsoon season, the emissions from rice residue burning in western India and eastern Pakistan could impact particulate air pollution in Lumbini and surrounding regions in southern Nepal. Therefore, our finding is meaningful and has a great importance for adopting the appropriate mitigation measures, not only at the local level but also by involving different regions and nations, to reduce the biomass burning emissions in the broader IGP region nations.

scholarly journals Organic molecular tracers in the atmospheric aerosols from Lumbini, Nepal, in the northern Indo-Gangetic Plain: influence of biomass burning

2017 ◽  
Vol 17 (14) ◽  
pp. 8867-8885 ◽  
Author(s):  
Xin Wan ◽  
Shichang Kang ◽  
Quanlian Li ◽  
Dipesh Rupakheti ◽  
Qianggong Zhang ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Vanillic Acid ◽  
Monsoon Season ◽  
Rural Site ◽  
Aerosol Composition ◽  
Gangetic Plain ◽  
Minimum Concentration ◽  
Post Monsoon ◽  
Post Monsoon Season ◽  
Indo Gangetic Plain

Abstract. To better understand the characteristics of biomass burning in the northern Indo-Gangetic Plain (IGP), total suspended particles were collected in a rural site, Lumbini, Nepal, during April 2013 to March 2014 and analyzed for the biomass burning tracers (i.e., levoglucosan, mannosan, vanillic acid). The annual average concentration of levoglucosan was 734 ± 1043 ng m−3 with the maximum seasonal mean concentration during post-monsoon season (2206 ± 1753 ng m−3), followed by winter (1161 ± 1347 ng m−3), pre-monsoon (771 ± 524 ng m−3) and minimum concentration during monsoon season (212 ± 279 ng m−3). The other biomass burning tracers (mannosan, galactosan, p-hydroxybenzoic acid, vanillic acid, syringic acid and dehydroabietic acid) also showed the similar seasonal variations. There were good correlations among levoglucosan, organic carbon (OC) and elemental carbon (EC), indicating significant impact of biomass burning activities on carbonaceous aerosol loading throughout the year in Lumbini area. According to the characteristic ratios, levoglucosan ∕ mannosan (lev ∕ man) and syringic acid ∕ vanillic acid (syr ∕ van), we deduced that the high abundances of biomass burning products during non-monsoon seasons were mainly caused by the burning of crop residues and hardwood while the softwood had less contribution. Based on the diagnostic tracer ratio (i.e., lev ∕ OC), the OC derived from biomass burning constituted large fraction of total OC, especially during post-monsoon season. By analyzing the MODIS fire spot product and 5-day air-mass back trajectories, we further demonstrated that organic aerosol composition was not only related to the local agricultural activities and residential biomass usage but also impacted by the regional emissions. During the post-monsoon season, the emissions from rice residue burning in western India and eastern Pakistan could impact particulate air pollution in Lumbini and surrounding regions in southern Nepal. Therefore, our finding is meaningful and has a great importance for adopting the appropriate mitigation measures, not only at the local level but also by involving different regions and nations, to reduce the biomass burning emissions in the broader IGP region nations.

scholarly journals Seasonal distribution and drivers of surface fine particulate matter and organic aerosol over the Indo-Gangetic Plain

2021 ◽  
Vol 21 (14) ◽  
pp. 10881-10909
Author(s):  
Caterina Mogno ◽  
Paul I. Palmer ◽  
Christoph Knote ◽  
Fei Yao ◽  
Timothy J. Wallington
Keyword(s):  
Particulate Matter ◽  
Monsoon Season ◽  
Fine Particulate Matter ◽  
Organic Aerosol ◽  
Substantial Contribution ◽  
Agricultural Crop ◽  
Gangetic Plain ◽  
Post Monsoon ◽  
Fine Particulate ◽  
Indo Gangetic Plain

Abstract. The Indo-Gangetic Plain (IGP) is home to 9 % of the global population and is responsible for a large fraction of agricultural crop production in Pakistan, India, and Bangladesh. Levels of fine particulate matter (mean diameter <2.5 µm, PM2.5) across the IGP often exceed human health recommendations, making cities across the IGP among the most polluted in the world. Seasonal changes in the physical environment over the IGP are dominated by the large-scale south Asian monsoon system that dictates the timing of agricultural planting and harvesting. We use the WRF-Chem model to study the seasonal anthropogenic, pyrogenic, and biogenic influences on fine particulate matter and its constituent organic aerosol (OA) over the IGP that straddles Pakistan, India, and Bangladesh during 2017–2018. We find that surface air quality during pre-monsoon (March–May) and monsoon (June–September) seasons is better than during post-monsoon (October–December) and winter (January–February) seasons, but all seasonal mean values of PM2.5 still exceed the recommended levels, so that air pollution is a year-round problem. Anthropogenic emissions influence the magnitude and distribution of PM2.5 and OA throughout the year, especially over urban sites, while pyrogenic emissions result in localised contributions over the central and upper parts of IGP in all non-monsoonal seasons, with the highest impact during post-monsoon seasons that correspond to the post-harvest season in the agricultural calendar. Biogenic emissions play an important role in the magnitude and distribution of PM2.5 and OA during the monsoon season, and they show a substantial contribution to secondary OA (SOA), particularly over the lower IGP. We find that the OA contribution to PM2.5 is significant in all four seasons (17 %–30 %), with primary OA generally representing the larger fractional contribution. We find that the volatility distribution of SOA is driven mainly by the mean total OA loading and the washout of aerosols and gas-phase aerosol precursors that result in SOA being less volatile during the pre-monsoon and monsoon season than during the post-monsoon and winter seasons.

scholarly journals Vertical and horizontal distribution of submicron aerosol chemical composition and physical characteristics across northern India during pre-monsoon and monsoon seasons

2019 ◽  
Vol 19 (8) ◽  
pp. 5615-5634 ◽  
Author(s):  
James Brooks ◽  
James D. Allan ◽  
Paul I. Williams ◽  
Dantong Liu ◽  
Cathryn Fox ◽  
...  
Keyword(s):  
Black Carbon ◽  
Mass Concentration ◽  
Monsoon Season ◽  
Western India ◽  
Aerosol Layer ◽  
Gangetic Plain ◽  
Submicron Aerosol ◽  
Aerosol Mass ◽  
Indo Gangetic Plain ◽  
Mass Concentrations

<p><strong>Abstract.</strong> The vertical distribution in the physical and chemical properties of submicron aerosol has been characterised across northern India for the first time using airborne in situ measurements. This study focusses primarily on the Indo-Gangetic Plain, a low-lying area in the north of India which commonly experiences high aerosol mass concentrations prior to the monsoon season. Data presented are from the UK Facility for Airborne Atmospheric Measurements BAe-146 research aircraft that performed flights in the region during the 2016 pre-monsoon (11 and 12 June) and monsoon (30 June to 11 July) seasons.</p> <p>Inside the Indo-Gangetic Plain boundary layer, organic matter dominated the submicron aerosol mass (43&amp;thinsp;%) followed by sulfate (29&amp;thinsp;%), ammonium (14&amp;thinsp;%), nitrate (7&amp;thinsp;%) and black carbon (7&amp;thinsp;%). However, outside the Indo-Gangetic Plain, sulfate was the dominant species, contributing 44&amp;thinsp;% to the total submicron aerosol mass in the boundary layer, followed by organic matter (30&amp;thinsp;%), ammonium (14&amp;thinsp;%), nitrate (6&amp;thinsp;%) and black carbon (6&amp;thinsp;%). Chlorine mass concentrations were negligible throughout the campaign. Black carbon mass concentrations were higher inside the Indo-Gangetic Plain (2&amp;thinsp;<span class="inline-formula">µ</span>g&amp;thinsp;m<span class="inline-formula"><sup>−3</sup></span>) compared to outside (1&amp;thinsp;<span class="inline-formula">µ</span>g&amp;thinsp;m<span class="inline-formula"><sup>−3</sup></span>). Nitrate appeared to be controlled by thermodynamic processes, with increased mass concentration in conditions of lower temperature and higher relative humidity. Increased mass and number concentrations were observed inside the Indo-Gangetic Plain and the aerosol was more absorbing in this region, whereas outside the Indo-Gangetic Plain the aerosol was larger in size and more scattered in nature, suggesting greater dust presence, especially in north-western India. The aerosol composition remained largely similar as the monsoon season progressed, but the total aerosol mass concentrations decreased by <span class="inline-formula">∼50</span>&amp;thinsp;% as the rainfall arrived; the pre-monsoon average total mass concentration was 30&amp;thinsp;<span class="inline-formula">µ</span>g&amp;thinsp;m<span class="inline-formula"><sup>−3</sup></span> compared to a monsoon average total mass concentration of 10–20&amp;thinsp;<span class="inline-formula">µ</span>g&amp;thinsp;m<span class="inline-formula"><sup>−3</sup></span>. However, this mass concentration decrease was less noteworthy (<span class="inline-formula">∼20</span>&amp;thinsp;%–30&amp;thinsp;%) over the Indo-Gangetic Plain, likely due to the strength of emission sources in this region. Decreases occurred in coarse mode aerosol, with the fine mode fraction increasing with monsoon arrival. In the aerosol vertical profile, inside the Indo-Gangetic Plain during the pre-monsoon, organic aerosol and absorbing aerosol species dominated in the lower atmosphere (<span class="inline-formula">&amp;lt;1.5</span>&amp;thinsp;km), with sulfate, dust and other scattering aerosol species enhanced in an elevated aerosol layer above 1.5&amp;thinsp;km with maximum aerosol height <span class="inline-formula">∼6</span>&amp;thinsp;km. The elevated concentration of dust at altitudes <span class="inline-formula">&amp;gt;1.5</span>&amp;thinsp;km is<span id="page5616"/> a clear indication of dust transport from the Great Indian Desert, also called the Thar Desert, in north-western India. As the monsoon progressed into this region, the elevated aerosol layer diminished, the aerosol maximum height reduced to <span class="inline-formula">∼2</span>&amp;thinsp;km. The dust and sulfate-dominated aerosol layer aloft was removed upon monsoon arrival, highlighted by an increase in fine mode fraction throughout the profile.</p>

scholarly journals Long term MAX-DOAS measurements of NO<sub>2</sub>, HCHO and aerosols and evaluation of corresponding satellite data products over Mohali in the Indo-Gangetic plain

2020 ◽  
Author(s):  
Vinod Kumar ◽  
Steffen Beirle ◽  
Steffen Dörner ◽  
Abhishek Kumar Mishra ◽  
Sebastian Donner ◽  
...  
Keyword(s):  
Monsoon Season ◽  
Ozone Production ◽  
Data Set ◽  
Gangetic Plain ◽  
Agricultural Residue ◽  
Modis Aod ◽  
Tropospheric No2 ◽  
The Difference ◽  
Indo Gangetic Plain

Abstract. We present comprehensive long term ground-based MAX-DOAS measurements of aerosols, nitrogen dioxide (NO2) and formaldehyde (HCHO) from Mohali (30.667° N, 76.739° E, 310 m above mean sea level), located in the densely populated Indo-Gangetic Plain (IGP) of India. We investigate the temporal variation and vertical profiles of aerosols, NO2 and HCHO and identify factors driving their ambient levels and distributions for the period from January 2013 to June 2017. We observed mean aerosol optical depth (AOD) at 360 nm, tropospheric NO2 vertical column density (VCD) and tropospheric HCHO VCD for the measurement period to be 0.63 ± 0.51, (6.7 ± 4.1) × 1015 molecules cm−2 and (13.2 ± 9.8) × 1015 molecules cm−2, respectively. Concerning the tropospheric NO2 VCDs, Mohali was found to be less polluted than urban and suburban locations of China and western countries, but comparable HCHO VCDs were observed. High tropospheric NO2 VCDs were observed in periods with enhanced biomass and biofuel combustion (e.g. agricultural residue burning and domestic burning for heating). Highest tropospheric HCHO VCDs were observed in agricultural residue burning periods with favourable meteorological conditions for photochemical formation, which in previous studies have shown an implication on high ambient ozone also over the IGP. Highest AOD is observed in the monsoon season, indicating possible hygroscopic growth of the aerosol particles. Most of the NO2 is located close to the surface, whereas significant HCHO is present at higher altitudes up to 600 meters. The vertical distribution of aerosol was found to be linked to the boundary layer height. The ground-based data set was also used for satellite validation. High-resolution MODIS AOD measurements correlate well but were systematically higher than MAX-DOAS AODs. NO2 VCDs from OMI correlate reasonably with MAX-DOAS VCDs, but are lower by ~ 30–50 % due to the difference in vertical sensitivities and the rather large OMI footprint. OMI HCHO VCDs exceed the MAX-DOAS VCDs by up to 30 %. For surface volume mixing ratio (VMR), MAX-DOAS NO2 measurements show a good correlation but a slight overestimation compared to the in situ measurements. However, for HCHO, a larger bias was observed due to large measurement uncertainties. The difference in vertical representativeness was found to be crucial for the observed biases in NO2 and HCHO inter-comparisons. Using the ratio of NO2 and HCHO VCDs measured from MAX-DOAS, we have found that the peak daytime ozone production regime is sensitive to both NOx and VOCs in winter but strongly sensitive to NOx in other seasons.

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