Darshan Singh

Effects of crop residue burning on aerosol properties, plume characteristics, and long‐range transport over northern India

Aerosol emissions from biomass burning are of specific interest over the globe due to their strong radiative impacts and climate implications. The present study examines the impact of paddy crop residue burning over northern India during the postmonsoon (October–November) season of 2012 on modification of aerosol properties, as well as the long-range transport of smoke plumes, altitude characteristics, and affected areas via the synergy of ground-based measurements and satellite observations. During this period, Moderate Resolution Imaging Spectroradiometer (MODIS) images show a thick smoke/hazy aerosol layer below 2–2.5 km in the atmosphere covering nearly the whole Indo-Gangetic Plains (IGP). The air mass trajectories originating from the biomass-burning source region over Punjab at 500 m reveal a potential aerosol transport pathway along the Ganges valley from west to east, resulting in a strong aerosol optical depth (AOD) gradient. Sometimes, depending upon the wind direction and meteorological conditions, the plumes also influence central India, the Arabian Sea, and the Bay of Bengal, thus contributing to Asian pollution outflow. The increased number of fire counts (Terra and Aqua MODIS data) is associated with severe aerosol-laden atmospheres (AOD500 nm > 1.0) over six IGP locations, high values of Angstrom exponent (>1.2), high particulate mass 2.5 (PM2.5) concentrations (>100–150 µgm−3), and enhanced Ozone Monitoring Instrument Aerosol Index gradient (~2.5) and NO2 concentrations (~6 × 1015 mol/cm2), indicating the dominance of smoke aerosols from agricultural crop residue burning. The aerosol size distribution is shifted toward the fine-mode fraction, also exhibiting an increase in the radius of fine aerosols due to coagulation processes in a highly turbid environment. The spectral variation of the single-scattering albedo reveals enhanced dominance of moderately absorbing aerosols, while the aerosol properties, modification, and mixing atmospheric processes differentiate along the IGP sites depending on the distance from the aerosol source, urban influence, and local characteristics.

Trends in aerosol optical depth over Indian region: Potential causes and impact indicators

The first regional synthesis of long-term (back to similar to 25 years at some stations) primary data (from direct measurement) on aerosol optical depth from the ARFINET (network of aerosol observatories established under the Aerosol Radiative Forcing over India (ARFI) project of Indian Space Research Organization over Indian subcontinent) have revealed a statistically significant increasing trend with a significant seasonal variability. Examining the current values of turbidity coefficients with those reported similar to 50 years ago reveals the phenomenal nature of the increase in aerosol loading. Seasonally, the rate of increase is consistently high during the dry months (December to March) over the entire region whereas the trends are rather inconsistent and weak during the premonsoon (April to May) and summer monsoon period (June to September). The trends in the spectral variation of aerosol optical depth (AOD) reveal the significance of anthropogenic activities on the increasing trend in AOD. Examining these with climate variables such as seasonal and regional rainfall, it is seen that the dry season depicts a decreasing trend in the total number of rainy days over the Indian region. The insignificant trend in AOD observed over the Indo-Gangetic Plain, a regional hot spot of aerosols, during the premonsoon and summer monsoon season is mainly attributed to the competing effects of dust transport and wet removal of aerosols by the monsoon rain. Contributions of different aerosol chemical species to the total dust, simulated using Goddard Chemistry Aerosol Radiation and Transport model over the ARFINET stations, showed an increasing trend for all the anthropogenic components and a decreasing trend for dust, consistent with the inference deduced from trend in Angstrom exponent.

Characteristics and emission budget of carbonaceous species from post-harvest agricultural-waste burning in source region of the Indo-Gangetic Plain

Characteristics and emission budget of carbonaceous species from two distinct post-harvest agricultural-waste (paddy- and wheat-residue) burning emissions have been studied from a source region (Patiala: 30.2°N, 76.3°E; 250 m amsl) in the Indo-Gangetic Plain (IGP), Northern India. The PM2.5 mass concentration varies from 60 to 390 µg m−3 during paddy-residue burning (October–November) with dominant contribution from organic carbon (OC≈33%), whereas contribution from elemental carbon (EC) centres at ~4%. Water-soluble organic carbon (WSOC) accounts for about 50% of OC. In contrast, mass concentration of PM2.5 during the period of wheat-residue burning (April–May) is significantly lower, varies from 18 to 123 µg m−3 and mass fractions of EC and OC are 7 and 26%, respectively. The diagnostic ratios of OC/EC (11±2), WSOC/OC (0.52±0.02), nss-K+/OC (0.06±0.00) and ΣPAHs/EC (4.3±0.7 mg/g) from paddy-residue burning emissions are significantly different than those from wheat-residue burning (OC/EC: 3.0±0.4; WSOC/OC: 0.60±0.03; nss-K+/OC: 0.14±0.01 and ΣPAHs/EC: 1.3±0.2 mg/g). The emission budget of OC, EC and ΣPAHs from post-harvest agricultural-waste burning in the IGP are estimated to be 505±68 Gg/y, 59±2 Gg/y and 182±32 Mg/y, respectively. From a global perspective, crop-residue burning in Northern India contributes nearly 20% of both OC and EC to the total emission budget from the agricultural-waste burning.

Impact of Two Intense Dust Storms on Aerosol Characteristics and Radiative Forcing over Patiala, Northwestern India

Impact of dust storms on the aerosol characteristics and radiative forcing over Patiala, northwestern India has been studied during April-June of 2010 using satellite observations and ground-based measurements. Six dust events (DE) have been identified during the study period with average values of Aqua-MODIS AOD550 and Microtops-II AOD500 over Patiala as and , respectively while Aura-OMI AI exhibits high values ranging from 2.01 to 6.74. The Angstrom coefficients α380–870 and β range from 0.12 to 0.31 and 0.95 to 1.40, respectively. The measured spectral AODs, the OPAC-derived aerosol properties and the surface albedo obtained from MODIS were used as main inputs in SBDART model for the calculation of aerosol radiative forcing (ARF) over Patiala. The ARF at surface (SRF) and top of atmosphere (TOA) ranges from ~−50 to −100 Wm−2 and from ~−10 to −25 Wm−2, respectively during the maximum of dust storms. The radiative forcing efficiency was found to be −66 Wm−2AOD−1 at SRF and −14 Wm−2AOD−1 at TOA. High values of ARF in the atmosphere (ATM), ranging between ~

Black Carbon and Elemental Carbon from Postharvest Agricultural-Waste Burning Emissions in the Indo-Gangetic Plain

We compare the mass concentrations of black carbon (BC) and elemental carbon (EC) from different emissions in the Indo-Gangetic Plain (IGP), using optical (Aethalometer; 880 nm) and thermooptical technique (EC-OC analyzer; 678 nm), respectively. The fractional contribution of BC mass concentration measured at two different channels (370 and 880 nm), OC/EC ratio, and non-sea-salt K

Optical and Radiative Properties of Aerosols over Two Locations in the North-West Part of India during Premonsoon Season

The present study examines the aerosol characteristics over two locations in the northwest region of India (Dehradun and Patiala) during premonsoon season of 2013. The average mass concentrations of particulates (PM10; PM2.5; PM1) were found to be , , and µgm−3 and , , and µgm−3 over Dehradun and Patiala, respectively. The average aerosol optical depth () is observed to be over Dehradun and over Patiala. Angstrom exponent and fine mode fraction show higher values over Dehradun as compared to Patiala. The average mass concentration of black carbon was found to be ngm−3 and ngm−3 over Dehradun and Patiala, respectively. The diurnal pattern of BC is mainly controlled by boundary layer dynamics and local anthropogenic activities over both the stations. The average single scattering albedo () exhibited low value over Patiala () in comparison to Dehradun (), suggesting the abundance of absorbing type aerosols over Patiala. The average atmospheric aerosol radiative forcing is

Dielectric investigations of pure and carbon nanotube-doped deformed helix ferroelectric liquid crystals

The doping of carbon nanotubes (CNTs) into liquid crystals enhances their parameters for use in various applications. Here, an attempt is made to study the effect of CNTs on the dielectric properties of the deformed helix ferroelectric liquid crystals mixture FLC-6304, in different liquid crystal phases. The inclusion of CNTs significantly affect the dielectric parameters in the chiral smectic C phase with an inversion of the effect near the transition to, and in, the chiral smectic A phase

Measuring electrical parameters of ferroelectric liquid crystals using universal current reversal method

The universal current reversal method is used for the simultaneous measurement of response time (τ), azimuthal angle (ϕo), spontaneous polarization (P S), and rotational viscosity (γϕ) of two ferroelectric liquid crystals (FLCs). The application of AC field in FLCs results in reorientational current, which is further analyzed to obtain various parameters. The variation in the parameters with temperature follows the typical trend predicted by the theory. The theoretical curve fits well into the experimental data. Its comparison with traditional current reversal method is confirmed to address certain limitations of that method.

Modification of the electrical parameters of CNT-doped deformed-helix ferro-electric liquid crystals

Liquid crystals are useful for a wide range of applications due to their exceptional properties. Doping of liquid crystals with carbon nanotubes (CNTs), even at very low concentrations, produces a detectable effect on the liquid crystal (LC) properties that can be very attractive for various functions. In this study, an attempt was made to investigate the effect of CNTs on the electrical properties of a short-pitch and high-spontaneous-polarization ferro-electric LC mixture, FLC-6304, at different temperatures. The inclusion of the CNTs significantly reduced the polarization at temperatures well within the SmC* phase, but the effect was gradually reversed as the transition temperature was approached. The insertion of the CNTs also reduced the response time and the rotational viscosity of the FLC mixture, which is highly desirable in the LCD industry.

Cell thickness dependence of liquid crystal parameters

Ferroelectric liquid crystal parameters, spontaneous polarization, and transition temperature were studied as a function of cell thickness. These parameters were found to increase with increasing cell thickness, but an exception was observed for the transition temperature in the case of a thin cell. A simple Landau model is presented to interpret the theoretical and experimental observations. The anomalous behavior is attributed to the electroclinic effect and is explained using the Landau model.