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The sprawling 852-acre IIT Jodhpur campus is a majestic tribute to the deep-rooted diverse cultural heritage of the region. The campus is an architectural masterpiece, which is slated to become an international exemplar of sustainability with net-zero energy, and advanced water and waste management strategies.&rdquo;

IIT Jodhpur

Many cities in India experience severe deterioration of air quality in winter. Particulate matter is a key atmospheric pollutant that impacts millions of people. In particular, the high mass concentration of particulate matter reduces visibility, which has severely damaged the economy and endangered human lives. But the underlying chemical mechanisms and physical processes responsible for initiating haze and fog formation remain poorly understood. Here we present the measurement results of chemical composition of particulate matter in Delhi and Chennai. We find persistently high chloride in Delhi and episodically high chloride in Chennai. These measurements, combined with thermodynamic modelling, suggest that in the presence of excess ammonia in Delhi, high local emission of hydrochloric acid partitions into aerosol water. The highly water-absorbing and soluble chloride in the aqueous phase substantially enhances aerosol water uptake through co-condensation, which sustains particle growth, leading to haze and fog formation. We therefore suggest that the high local concentration of gas-phase hydrochloric acid, possibly emitted from plastic-contained waste burning and industry, causes some 50% of the reduced visibility. Our work implies that identifying and regulating gaseous hydrochloric acid emissions could be critical to improve visibility and human health in India. © 2021, The Author(s), under exclusive licence to Springer Nature Limited.

World University root node

Department of Civil & Infrastructure Engineering

School of Liberal Arts (SoLA)

Nature Geoscience

Enhanced aerosol particle growth sustained by high continental chlorine emission in India

The sensitive ecosystem of the central Himalayan (CH) region, which is experiencing enhanced stress from anthropogenic forcing, requires adequate atmospheric observations and an improved representation of the Himalaya in the models. However, the accuracy of atmospheric models remains limited in this region due to highly complex mountainous topography. This article delineates the effects of spatial resolution on the modeled meteorology and dynamics over the CH by utilizing the Weather Research and Forecasting (WRF) model extensively evaluated against the Ganges Valley Aerosol Experiment (GVAX) observations during the summer monsoon. The WRF simulation is performed over a domain (d01) encompassing northern India at 15 km-15 km resolution and two nests (d02 at 5 km-5 km and d03 at 1 km-1 km) centered over the CH, with boundary conditions from the respective parent domains. WRF simulations reveal higher variability in meteorology, e.g., relative humidity (RHD70.3 % 96.1 %) and wind speed (WSD1.1 4.2ms-1), compared to the ERA-Interim reanalysis (RHD80.0 % 85.0 %, WSD1.2 2.3ms-1) over northern India owing to the higher resolution. WRF-simulated temporal evolution of meteorological variables is found to agree with balloon-borne measurements, with stronger correlations aloft (r D0.44 0.92) than those in the lower troposphere (r D0.18 0.48). The model overestimates temperature (warm bias by 2.8 C) and underestimates RH (dry bias by 6.4 %) at the surface in d01. Model results show a significant improvement in d03 (P D827.6 hPa, T D19.8 C, RHD92.3 %), closer to the GVAX observations (P D801.4 hPa, T D19.5 C, RHD94.7 %). Interpolating the output from the coarser domains (d01, d02) to the altitude of the station reduces the biases in pressure and temperature; however, it suppresses the diurnal variations, highlighting the importance of well-resolved terrain (d03). Temporal variations in near-surface P, T , and RH are also reproduced by WRF in d03 to an extent (r&gt;0:5). A sensitivity simulation incorporating the feedback from the nested domain demonstrates the improvement in simulated P, T , and RH over the CH. Our study shows that the WRF model setup at finer spatial resolution can significantly reduce the biases in simulated meteorology, and such an improved representation of the CH can be adopted through domain feedback into regional-scale simulations. Interestingly, WRF simulates a dominant easterly wind component at 1 km-1 km resolution (d03), which is missing in the coarse simulations; however, the frequency of southeasterlies remains underestimated. The model simulation implementing a highresolution (3 s) topography input (SRTM) improved the prediction of wind directions; nevertheless, further improve- ments are required to better reproduce the observed localscale dynamics over the CH. © 2021 EDP Sciences. All rights reserved.

Fulltext

Geoscientific Model Development

Effects of spatial resolution on WRF v3.8.1 simulated meteorology over the central Himalaya

Dry deposition is a major sink for tropospheric ozone; nevertheless, studies on its effects on ozone distribution are very limited over the rapidly developing South Asian region. We performed numerical simulations using the regional model WRF-Chem (Weather Research and Forecasting Model coupled with chemistry) to investigate the effect of dry deposition on surface ozone over this region by switching dry deposition ON-OFF in the model. Dry deposition of ozone is found to reduce ozone mixing ratios by up to ∼ 40% over the Indo-Gangetic Plain (IGP) and parts of western and central India. Additional enhancements (by up to ∼ 5 ppbv) in ozone are simulated when dry deposition for all gaseous species is switched off. We find a significant contrast on the effects of dry deposition from station to station as well as on the diurnal timescales over this region. The enhancements in ozone, caused by the absence of dry deposition, are lower over urban stations during nighttime, as compared to the rural and high-altitude stations. Significant enhancements in ozone levels in the absence of dry deposition over the mostly agrarian IGP underpin the importance of dry deposition particularly in the vegetated areas. The South Asian ecosystem is seen to act as an important sink of surface ozone via the dry deposition. The analyses partially fill a gap in the studies of dry deposition over the South Asian region, where this sink is anticipated to get perturbed following the changes in land use and land cover. Copyright © 2020 American Chemical Society.

ACS Earth and Space Chemistry

Effects of Dry Deposition on Surface Ozone over South Asia Inferred from a Regional Chemical Transport Model

Fine particulate matter (PM2.5, aerodynamic diameter ≤2.5 µm) impacts the climate, reduces visibility and severely influences human health. The Indo-Gangetic Plain (IGP), home to about one-seventh of the world’s total population and a hotspot of aerosol loading, observes strong enhancements in the PM2.5 concentrations towards winter. We performed high-resolution (12 km × 12 km) atmospheric chemical transport modeling (WRF-Chem) for the post-monsoon to winter transition to unravel the underlying dynamics and influences of regional emissions over the region. Model, capturing the observed variations to an extent, reveals that the spatial distribution of PM2.5 having patches of enhanced concentrations (≥100 µgm−3) during post-monsoon, evolves dramatically into a widespread enhancement across the IGP region during winter. A sensitivity simulation, supported by satellite observations of fires, shows that biomass-burning emissions over the northwest IGP play a crucial role during post-monsoon. Whereas, in contrast, towards winter, a large-scale decline in the air temperature, significantly shallower atmospheric boundary layer, and weaker winds lead to stagnant conditions (ventilation coefficient lower by a factor of ~4) thereby confining the anthropogenic influences closer to the surface. Such changes in the controlling processes from post-monsoon to winter transition profoundly affect the composition of the fine aerosols over the IGP region. The study highlights the need to critically consider the distinct meteorological processes of west-to-east IGP and changes in dominant sources from post-monsoon to winter in the formulation of future pollution mitigation policies. © 2020, The Author(s).

Scientific Reports

On the widespread enhancement in fine particulate matter across the Indo-Gangetic Plain towards winter

Crop Yield Loss (CYL) due to surface ozone substantially affects the Indian economy and the food availability for a billion residents. Nevertheless, the incurring losses over India remain uncertain due to limited measurements and significant uncertainties in the surface O3 simulated by chemistry-transport models, amongst other causes. Here, we revisit the ozone-attributable CYL using WRF-Chem model, with a set up previously shown to better reproduce the observed ozone variations over the contrasting chemical environments across the Indian region. WRF-Chem simulated ozone fields are converted to Accumulated Ozone above a Threshold of 40 ppbv (AOT40) for two primary crop growing seasons in India, i.e. Kharif (mid-June to mid-September), and Rabi (December to February). Relative Yield Losses (RYL) for wheat are found to be higher (∼21–26%) than those in a recent study based on observations (∼15%), as the model accounts for the rural chemistry which can be different from urban/suburban/high altitude environments where measurements are largely conducted. Additionally, RYL for rice estimated here (∼6%) is 3 times greater than a previous study using this model at a relatively coarser resolution to derive average surface ozone with a set of simulations with varying emission inventories, not evaluated in detail before deriving crop losses. The economic losses due to CYL estimated in this study (∼5 billion USD for wheat and 1.5 billion USD for rice) are on the higher side, when estimations from various studies are inter-compared (0.6–4.3 billion USD for wheat, and 0.5–1.5 billion USD for rice), for which increasing crop prices is also a contributing factor. Our study highlights an urgent need to conduct strategic ozone observations especially over agricultural fields, and the development of yearly regional-emission database to support policy making in India. © 2019 The Authors

Atmospheric Environment: X

Revisiting the crop yield loss in India attributable to ozone

We evaluate numerical simulations of surface ozone mixing ratios over the south Asian region during the pre-monsoon season, employing three different emission inventories in the Weather Research and Forecasting model with Chemistry (WRF-Chem) with the second-generation Regional Acid Deposition Model (RADM2) chemical mechanism: the Emissions Database for Global Atmospheric Research - Hemispheric Transport of Air Pollution (EDGAR-HTAP), the Intercontinental Chemical Transport Experiment phase B (INTEX-B) and the Southeast Asia Composition, Cloud, Climate Coupling Regional Study (SEAC4RS). Evaluation of diurnal variability in modelled ozone compared to observational data from 15 monitoring stations across south Asia shows the model ability to reproduce the clean, rural and polluted urban conditions over this region. In contrast to the diurnal average, the modelled ozone mixing ratios during noontime, i.e. hours of intense photochemistry (11:30-16:30gIST - Indian Standard Time - UTC +5:30), are found to differ among the three inventories. This suggests that evaluations of the modelled ozone limited to 24gh average are insufficient to assess uncertainties associated with ozone buildup. HTAP generally shows 10-30gppbv higher noontime ozone mixing ratios than SEAC4RS and INTEX-B, especially over the north-west Indo-Gangetic Plain (IGP), central India and southern India. The HTAP simulation repeated with the alternative Model for Ozone and Related Chemical Tracers (MOZART) chemical mechanism showed even more strongly enhanced surface ozone mixing ratios due to vertical mixing of enhanced ozone that has been produced aloft. Our study indicates the need to also evaluate the O3 precursors across a network of stations and the development of high-resolution regional inventories for the anthropogenic emissions over south Asia accounting for year-to-year changes to further reduce uncertainties in modelled ozone over this region. © Author(s) 2017.