Alok Kumar Pandey

Satellite and ground-based seasonal variability of NO2 and SO2 over New Delhi, India

Remote sensing technology application emerges as a useful tool for exploring atmospheric pollution revelation in the last two decade. In this study, we used Aura satellite Ozone Monitoring Instrument (OMI) tropospheric NO2 and pbl SO2 retrieval data (October 2004 – September 2013) to generate a composite spatial map of different seasons over New Delhi National Capital Region (NCR). For surface measurements, we used Central Pollution Control Board (CPCB) NO2 and SO2 data (January 2005 – December 2013). Further, we compared the satellite retrievals data to the surface measurements. A higher NO2 concentration in both OMI and CPCB stations measurements are obtained in winter season followed by summer and minimum in monsoon months. OMI SO2 concentration is higher in monsoon months and almost comparable in summer and winter seasons. We obtained a statistically significant correlation between OMI tropospheric NO2 and CPCB surface measurements.

Seasonal variation in spectral global and direct solar irradiances over a megacity Delhi

The present study investigates the spectral distribution of global, direct (Ebλ) and diffuse (Ebλ) irradiances over Delhi with the help of handheld Field Spectroradiometer in the year 2014 – 2015. Seasonal variation in the solar irradiances as well as the diffuse-to-direct ratio ( Edλ/Ebλ]) was studied during three seasons (post-monsoon, winter and pre-monsoon) having different atmospheric conditions. Observations were carried out under clear sky days during day time when solar zenith angle is low in order to get maximum solar radiation. The ratio Edλ/Ebλ is used as a function to measure the impact of aerosol load on incoming solar irradiance. NASAs Aqua satellite, MODIS (Moderate Resolution Imaging Spectroradiometer) AOD550 data has been used to evaluate the relationship between aerosol load and ratio (Edλ/Ebλ) on incoming solar radiation. A strong dependence of measured diffuse-to-direct irradiance ratio (Edλ/Ebλ) on wavelength was observed. It was found to be decreasing exponentially with wavelength. Value of Edλ/Ebλ was found to be maximum and minimum during Post-monsoon and Pre-monsoon seasons respectively. Also, the maximum values of Edλ/Ebλ ratio were observed at the shorter wavelengths in all the studied seasons. The AOD550 value was found to be maximum during postmonsoon followed by winter and Pre-monsoon seasons. Crop residue burning in addition to low wind speed was responsible for high aerosol load during the post-monsoon season where as inversion layer and calm wind conditions favored high aerosol load during winter season. A strong relation between the ratio Edλ/Ebλ and AOD550 is observed in all the studied seasons, indicating that high aerosol load was responsible for the attenuation of the incoming solar radiation in all the seasons

Seasonal variability of aerosols and their characteristics in urban and rural locations of Delhi-NCR

Present study shows the seasonal variation of the Aerosol Optical Depth (AOD) and aerosols characteristics in an urban and rural environment over Delhi-NCR. Aerosol sampling was carried out using a Mini-Volume sampler at an urban and rural location in Delhi-NCR. A relatively higher PM2.5 (particulate matter of size < 2.5 μm) concentrations were observed at the urban sampling site than the rural one in the summer as well as winter season. PM2.5 samples were further analyzed by Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDX) in order to understand the morphology and elemental composition of the PM2.5 aerosols. Summer SEM results showed the dominance of fluffy agglomerate (soot) in urban area whereas the rural area was relatively clean. The winter season SEM results showed the presence of aggregates of smaller particles at urban site whereas flaky, round and irregular shaped particles were observed at the rural site. EDX analysis showed the presence of elements such as C, Cu, Zn, Ga and Fe (representative elements) in varying concentrations at both the urban and rural sampling locations. NASA’s Aqua satellite MODIS sensor AOD data for summer and winter seasons have been used to study the spatial distributions of aerosols over the study region. AOD was found to be relatively higher in urban area as compared to the rural area in both the summer and winter seasons indicating the contribution of high amount of anthropogenic aerosols in the urban atmosphere.

Assessment of Source Profile of Nonmethane Hydrocarbon in the Ambient Air of Metro City Delhi, India

To link to this article: http://dx.doi.org/10.12944/CWE.12.2.16 Abstract In this paper presents the assessment of source profile of nonmethane hydrocarbons (NMHCs) in the ambient air of Delhi. The samples were collected from five different urban sites using tedlar bags for aliphatic NMHCs and activated adsorption charcoal tubes for aromatic NMHCs during October 2014 to September 2015. Eleven aliphatic NMHCs propane, n-butane i-butene, i-butane, 1,3-butadiene, trans-2-butene, cis-2-pentene, n-pentane, n-hexane, heptane and four aromatic NMHCs benzene, toluene, o-xylene, p/m-xylene were identified in 112 urban ambient air samples. Samples were analysed using gas chromatography which is coupled with flame ionization detector (GC-FID). Pearson correlation coefficient (r) found to be = 0.5±0.2, shows significance level to have moderate among the NMHCs, indicates NMHCs in the urban ambient air have many sources profile mentioned in PCA result. Factor analysis (FA) and receptor model, i.e., Principal Component Analysis (PCA)/Absolute Principal Component Score (APCS) was used for identification of source profile distribution. PCA analysis after the varimax rotation have identified six possible source profile and explained about 70 % of the total data set. The average % contribution of NMHCs emitted from vehicles was found to be 23%, whereas polymer manufacturing industries contributes 19% and from refinery operation/ gas station contribute 14%, and 13%, emitted from flare emissions and 10% from natural gas emissions. The secondary industrial process, including paints, body soaps and metal fabricator and processing was contributing 8%. Out of these remaining 13% was estimated as unidentified sources. These findings may be used by government authorities to formulate policies and strategies for improvement of urban air quality that can improve the health of urban communities. Article History

Spatial variation of Aerosol Optical Depth and Solar Irradiance over Delhi -NCR during Summer season

Introduction Aerosol and air pollution play a crucial role in the urban climatology. Urbanization, industrial development, biomass burning and fossil fuel combustion processes due to growing anthropogenic activities have led to increasing the air pollution Abstract Present study shows the spatial variation of Aerosol Optical Depth (AOD), solar irradiance and their association at the urban and rural sites in Delhi and National Capital Region (NCR) during the summer season of the year 2015. Summer-time AOD data from the NASA’s Terra satellite MODIS sensor has been used to study the spatial distribution of aerosols over Delhi and its surrounding rural area. The ground data for the direct and global solar irradiances was collected over this region at urban and rural locations in Delhi and NCR using a Fieldspec Spectro-radiometer. HYSPLIT model has been used for the air mass trajectory analysis. The AOD values were observed to be higher over Delhi compared to the relatively lower AOD in rural area of NCR. The NCR site observed higher average solar irradiances than Delhi during the summer season. This may be because of the higher aerosol concentration in Delhi as compared to its outskirts. Also, this region is affected by the severe dust storm events during the summer season which further increases the aerosol load in the atmosphere. HYSPLIT results show the influence of western Thar Desert air masses on the Delhi-NCR. Windblown as well anthropogenic aerosols play a major role in scattering and absorption of the incoming solar radiation and hence, in governing the micro-climatology of the region. Article history

Dynamics of thermal inertia over highly urban city: a case study of Delhi

This paper focuses on thermal inertia estimation of Delhi and its surrounding areas during summer season based on the diurnal temperature variations and albedo information of the region retrieved from satellite data. The study involves mapping of day and night time surface temperatures and the blue sky albedo (actual albedo on ground) over the study region using Moderate Resolution Imaging Spectroradiometer (MODIS) datasets. The study reveals that Delhi is cooler than its surrounding regions during the day time, showing the formation of cool island. On the contrary, temperature inside the city is much higher than its surrounding rural regions during the night time, thus confirming the formation of nocturnal heat island. The day and night time temperature maps are then used to obtain the diurnal temperature range and together with albedo maps of the study region, are used to estimate the thermal inertia over the region. The study reveals that the dense built-up urban area of Delhi has higher thermal inertia than that of the surrounding rural areas during the summer season. The spatial variation of thermal inertia over the region is found to explain the occurrence of day-time cool island reasonably well.