For more than 2 decades, crop residues in Punjab, a region spanning northwestern India and eastern Pakistan, have been burned during October and November to ready fields for the next year's planting. This practice poses a serious threat to air quality in South Asia. ©2014. American Geophysical Union. All Rights Reserved.

Singh R.P.

Kaskaoutis D.G.

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Shiv Nadar University

Crop Residue Burning: A Threat to South Asian Air Quality

Long-term trends in surface-level particulate matter of dynamic diameter ≤2 µm (PM2) in regard to air quality observations over Greater Hyderabad Region (GHR), India are estimated by the synergy of ground-based measurements and satellite observations during the period 2001–2013 (satellite) and July 2009–Dec 2013 (ground-based). Terra Moderate Resolution Imaging Spectroradiometer (MODIS)-derived aerosol optical thickness (AOT) (MODIS-AOTs) was validated against that measured from Microtops-II Sunphotometer (MTS) AOTs (MTS-AOTs) and then utilized to estimate surface-level PM2 concentrations over GHR using regression analysis between MODIS-AOTs, MTS-AOTs, and measured PM2. In general, the MODIS-estimated PM2 concentrations fell within the uncertainty of the measurements, thus allowing the estimate of PM2 from MODIS, although in some cases they differed significantly due to vertical heterogeneity in aerosol distribution and the presence of distinct elevated aerosol layers of different origin and characteristics. Furthermore, significant spatial and temporal heterogeneity in the AOT and PM2 estimates is observed in urban environments, especially during the pre-monsoon and monsoon seasons, which reduces the accuracy of the PM2 estimates from MODIS. The estimates of PM2 using MTS or MODIS-AOT exhibit a root mean square deference (RMSD) of about 8–16\% against measured PM2 on a seasonal basis. Furthermore, a tendency of increasing PM2 concentrations is observed, which however is difficult to quantify for urban areas due to uncertainties in PM2 estimations and gaps in the data set. Examination of surface and columnar aerosol concentrations, along with meteorological parameters from radiosonde observations on certain days, reveals that changes in local emissions and boundary-layer dynamics, and the presence or arrival of distinct aerosol plumes aloft, are major concerns in the accurate estimation of PM2 from MODIS, while the large spatial distribution of aerosol and pollutants in the urban environment makes such estimates a considerable challenge. © 2015 Taylor & Francis.

International Journal of Remote Sensing

Estimation of particulate matter from satellite- and ground-based observations over Hyderabad, India

Particulate matter (PM2.5) samples were collected over Delhi, India during January to December 2012 and analysed for carbonaceous aerosols and inorganic ions (SO42- and NO3-) in order to examine variations in atmospheric chemistry, combustion sources and influence of long-range transport. The PM2.5 samples are measured (offline) via medium volume air samplers and analysed gravimetrically for carbonaceous (organic carbon, OC; elemental carbon, EC) aerosols and inorganic ions (SO42- and NO3-). Furthermore, continuous (online) measurements of PM2.5 (via Beta-attenuation analyser), black carbon (BC) mass concentration (via Magee scientific Aethalometer) and carbon monoxide (via CO-analyser) are carried out. PM2.5 (online) range from 18.2 to 500.6μgm-3 (annual mean of 124.6±87.9μgm-3) exhibiting higher night-time (129.4μgm-3) than daytime (103.8μgm-3) concentrations. The online concentrations are 38\% and 28\% lower than the offline during night and day, respectively. In general, larger night-time concentrations are found for the BC, OC, NO3-and SO42-, which are seasonally dependent with larger differences during late post-monsoon and winter. The high correlation (R2=0.74) between OC and EC along with the OC/EC of 7.09 (day time) and 4.55 (night-time), suggest significant influence of biomass-burning emissions (burning of wood and agricultural waste) as well as secondary organic aerosol formation during daytime. Concentrated weighted trajectory (CWT) analysis reveals that the potential sources for the carbonaceous aerosols and pollutants are local emissions within the urban environment and transported smoke from agricultural burning in northwest India during post-monsoon. BC radiative forcing estimates result in very high atmospheric heating rates (~1.8-2.0Kday-1) due to agricultural burning effects during the 2012 post-monsoon season. © 2015 Elsevier B.V.

Science of the Total Environment

Carbonaceous aerosols and pollutants over Delhi urban environment: Temporal evolution, source apportionment and radiative forcing

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 500m 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&gt;1.0) over six IGP locations, high values of Ångström exponent (&gt;1.2), high particulate mass 2.5 (PM2.5) concentrations (&gt;100-150 µgm-3), and enhanced Ozone Monitoring Instrument Aerosol Index gradient (~2.5) and NO2 concentrations (~6 × 1015mol/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. © 2014. American Geophysical Union. All Rights Reserved.

Journal of Geophysical Research

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

Journal of Geophysical Research: Atmospheres

Air pollution over the Ganges basin and northwest Bay of Bengal in the early postmonsoon season based on NASA MERRAero data

Atmospheric Research

Patterns of fire activity over Indonesia and Malaysia from polar and geostationary satellite observations

Atmospheric Environment

Synergistic analyses of optical and microphysical properties of agricultural crop residue burning aerosols over the Indo-Gangetic Basin (IGB)

Environmental Monitoring and Assessment

Influence of coal-based thermal power plants on the spatial–temporal variability of tropospheric NO 2 column over India

Crop residue burning: A threat to South Asian air quality