Assessment of biomass burning and fossil fuel contribution to black carbon concentrations in Delhi during winter

Year-long variability of the fossil fuel and wood burning black carbon components at a rural site in southern Delhi outskirts

Air pollution has large impacts on the Hindu Kush Himalaya (HKH), affecting not just the health of people and ecosystems, but also climate, the cryosphere, monsoon patterns, water availability, agriculture, and incomes (established but incomplete). Although the available data are not comprehensive, they clearly show that the HKH receives significant amounts of air pollution from within and outside of the region, including the Indo-Gangetic Plain (IGP), a region where many rural areas are severely polluted. In addition, the HKH receives trans-boundary pollution from other parts of Asia. This chapter surveys the evidence on regional air pollution and considers options for reducing it, while underlining the need for regional collaboration in mitigation efforts. As described in Chap. 1, the HKH region is fragile and rapidly changing; while the outcome of the interplay of complex drivers is difficult to predict, it will have major consequences. That holds true for air pollution as well.

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Air Pollution in the Hindu Kush Himalaya

Urban areas in developing countries are major sources of carbonaceous aerosols and air pollutants, pointing out the need for a detailed assessment of their levels and origin close to the source. A multi-instrument research campaign was performed in Delhi during December 2015–February 2016 aimed at exploring the pollution levels and the contribution of various sources to particulate matter (PM) concentrations, black carbon (BC) aerosols, and trace gases. The weak winds (< 5–6 m s−1) along with the shallow boundary layer favoured the formation of thick and persistent fog conditions, which along with the high BC (24.4 ± 12.2 μg m−3) concentrations lead to the formation of smog. Very high pollution levels were recorded during the campaign, with mean PM10, PM2.5, CO, NO, and O3 concentrations of 245.5 ± 109.8 μg m−3, 145.5 ± 69.5 μg m−3, 1.7 ± 0.5 ppm, 7.9 ± 2.3 ppb, and 31.3 ± 18.4 ppb, respectively. This study focuses on examining the daily/diurnal cycles of the aerosol optical properties (extinction, scattering, absorption coefficients, single scattering albedo), as well as of PM and other pollutant concentrations, along with changes in meteorology (mixing-layer height and wind speed). In addition, the hot-spot pollution sources in the greater Delhi area were determined via bivariate plots and conditional bivariate probability function (CBPF), while the distant sources were examined via the concentration weighted trajectory (CWT) analysis. The results show that the highest aerosol absorption and scattering coefficients, PM, and trace gas concentrations are detected for weak winds (< 2 m s−1) with a preference for eastern directions, revealing high contribution from local sources and accumulation of pollutants within urban Delhi.

Aerosol and pollutant characteristics in Delhi during a winter research campaign

Stable and clear atmospheric conditions, lower surface temperatures, an ample moisture supply, and a strong low-level inversion persisting for most of the night usually facilitates the formation of dense fog during winter in Delhi. This severely hinders the flight operations at India’s busiest airport, the Indira Gandhi International (IGI) Airport, where more than 900 flight operations occur per day and an interruption can cause significant financial losses to the aviation industry. It is important to undertake a quantitative study of the estimated losses. This study, undertaken for the first time in India, aimed to evaluate the impact of dense fog at IGI Airport on economic losses which occurred during the winter season between 2011 and 2016. The breakdown of charges for different segments of flight operations for the domestic and international sectors was obtained from India’s Ministry of Civil Aviation and the Center for Asia Pacific Aviation (CAPA) India. A total of 653 h of dense fog between 2011 and 2016 at IGI Airport caused economic losses of approximately 3.9 million USD (248 million Indian rupees) to the airlines. The analysis further found that from 2014–2015 onwards, there has been a reduction in the number of flight delays, diversions, and cancellations by approximately 88%, 55%, and 36%, respectively, due to the strict implementation of guidelines to facilitate the Category (CAT)-III landing for aircraft during dense fog.

Loss to Aviation Economy Due to Winter Fog in New Delhi during the Winter of 2011–2016

The objectives of the Winter Fog Experiment (WIFEX) over the Indo-Gangetic Plains of India are to develop better now-casting and forecasting of winter fog on various time-and spatial scales. Maximum fog occurrence over northwest India is about 48 days (visibility <1000 m) per year, and it occurs mostly during the December-February time-period. The physical and chemical characteristics of fog, meteorological factors responsible for its genesis, sustenance, intensity and dissipation are poorly understood. Improved understanding on the above aspects is required to develop reliable forecasting models and observational techniques for accurate prediction of the fog events. Extensive sets of comprehensive ground-based instrumentation were deployed at the Indira Gandhi International Airport, New Delhi. Major in situ sensors were deployed to measure surface micrometeorological conditions, radiation balance, turbulence, thermodynamical structure of the surface layer, fog droplet and aerosol microphysics, aerosol optical properties, and aerosol and fog water chemistry to describe the complete environmental conditions under which fog develops. In addition, Weather Forecasting Model coupled with chemistry is planned for fog prediction at a spatial resolution of 2 km. The present study provides an introductory overview of the winter fog field campaign with its unique instrumentation.

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Winter fog experiment over the Indo-Gangetic plains of India

 Continuous aerosol and cloud condensation nuclei (CCN) measurements carried out at the ground
observational facility situated in the rain-shadow region of the Indian subcontinent are
illustrated These observations were part of the Cloud Aerosol Interaction Precipitation
Enhancement Experiment (CAIPEEX) during the Indian summer monsoon season (June to September) of
2018 Observations are classified as dry–continental (monsoon break) and wet–marine (monsoon
active) according to the air mass history CCN concentrations measured for a range of
supersaturations (02 %–12 %) are parameterized using Twomey's empirical relationship CCN
concentrations at low (02 %) supersaturation (SS) were high ( > 1000 cm - 3 ) during
continental conditions and observed together with high black carbon
( BC ∼ 2000 ng m - 3 ) and columnar aerosol loading During the marine air
mass conditions, CCN concentrations diminished to ∼ 350 cm - 3 at 03 % SS and
low aerosol loading persisted ( BC ∼ 800 ng m - 3 ) High CCN activation
fraction (AF) of ≅055 (at 03 % SS) was observed before the monsoon rainfall, which
reduced to ≅015 during the marine air mass and enhanced to ≅032 after that There was mostly
monomodal aerosol number size distribution (NSD) with a mean geometric mean diameter (GMD) of
 ≅85 nm , with least ( ≅9  %) contribution from nucleation mode
( nm ) particles persisted before the monsoon, while multimode NSD with
 ≅19  % of nucleation mode particles was found during the marine air mass Critical
activation diameters ( dcri ) for 03 % SS were found to be about 72, 169, and
121  nm prior to, during, and after the marine conditions, respectively The better
association of CCN with aerosol absorption, and the concurrent accumulation mode particles during
continental conditions, points to the possibility of aged (oxygenated) carbonaceous aerosols
enhancing the CCN activity prior to the marine conditions An enhancement in CCN concentrations and
 k  values during the daytime along with absorption Angstrom exponent was observed during the
marine conditions Best closure obtained using measured critical diameter and ammonium sulfate
composition during continental conditions emphasizes the role of aged aerosols contributing to the
accumulation mode, enhancing the CCN efficiency The overestimation of CCN and less
hygroscopicity of accumulation mode aerosols during the marine air mass indicate the role of
size-dependent aerosol composition in CCN activity during the period

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Cloud condensation nuclei characteristics during the Indian summer monsoon over a rain-shadow region

. Continuous aerosol and Cloud Condensation Nuclei (CCN) measurements carried out at the ground observational facility situated in the rain-shadow region of the Indian sub-continent are illustrated. These observations were part of the Cloud-Aerosol Interaction Precipitation Enhancement EXperiment (CAIPEEX) during the Indian Summer Monsoon season (June to September) of 2018. Observations are classified as dry-continental (monsoon break) and wet-marine (monsoon active) according to air mass history. CCN concentrations measured for a range of supersaturations (0.2–1.2 %) are parameterized using Twomey's empirical relationship. CCN concentrations even at low (0.2 %) supersaturation (SS) were high (> 1,000 cm-3) during continental conditions associated with high black carbon (BC~2,000 ng m-3) and columnar aerosol loading. During the marine air mass conditions, CCN concentrations diminished to ~ 350 cm-3 at 0.3 % SS and low aerosol loading persisted (BC~900 ng m-3). High CCN activation fraction (AF) of ~ 0.55 (at 0.3 % SS) were observed before the monsoon rainfall, which reduced to ~ 0.15 during the monsoon and enhanced to ~ 0.32 after that. Mostly mono-modal aerosol number-size distribution (NSD) with a mean geometric mean diameter (GMD) of ~ 85 nm, with least (~ 9 %) contribution from nucleation mode (

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Jaya Rao

Papers

Winter fog experiment over the Indo-Gangetic plains of India

Cloud condensation nuclei characteristics during the Indian summer monsoon over a rain-shadow region

CCN characteristics during the Indian Summer Monsoon over a rain-shadow region