The National Metrology Institute of India and A Premier Research Laboratory in the Field of Physical Sciences
Changing Atmospheric Environment, its processes and impacts

Study of longterm variation of stratospheric ozone over Indian subcontinent

Version 8 SBUV on Nimbus 7 and SBUV/2 data on NOAA 9, 11, and 16 are used to find trend in stratospheric ozone. Vertical profiles of ozone over Delhi, Pune and Varanasi are obtained in mixing ratio on 15 pressure surfaces by averaging data within a grid of ± 20 latitude and ± 100 longitude around the respective station. A depletion in upper stratospheric ozone is found when SBUV + SBUV/ 2 data for the period 1978-2003 is analysed. Short term trend analysis for the periods 1978-92, 1992- 99 and 1999-03 have also been done.

Long term and short variation in vertical distribution of ozone and temperature over India and South East Asia

Focus on research on stratospheric ozone and total ozone has shifted recently to research on tropospheric ozone, in particular, surface ozone and its precursor gases due to its impact on regional air quality and climate.

(a) Long term variation in tropospheric ozone

Emissions of trace gases and aerosol from biofuels

The linkages between sources and concentration of atmospheric trace gases and aerosol are to be established to understand budget of trace gases and aerosol. Moreover, role of long range transport of pollutants over India could be quantified provided quantification of the emission/ contribution of pollutants from India itself is available. Sampling of biofuels was performed almost in district level over Delhi to determine emission factors of carbonaceous aerosol (Organic carbon and elemental carbon). The biomass collection sites in and around is shown in Fig. 6.16.

Long range transport of pollutants

The impact of long range transport of pollutant at several remote sites (Darjeeling, Hanle, Port Blair and Sunderban etc) was studied. To start with, the long term measurement of trace gases at Goa is being initiated, whereas, similar measurement is being started at Darjeeling in collaboration with Bose Institute, Kolkata. Measurement of surface ozone at Hanle and Port Blair is continuing in collaboration with Indian Institute of Astrophysics and India Meteorological Department respectively.

Polar Atmospheric studies

Photochemical reactions in snow have recently witnessed an unprecedented surge of interest. In recent investigations, it is seen that production and significant release of CO flux is from snow covered region. On the basis of measurements made at Maitri, Antarctica, it has been observed a systematical diurnal cycle coinciding with the diurnal cycle of solar actinic radiation. This variation implies that photochemical production of CO is active in the snow covered region of Antarctica.

Aerosol radiation forcing (ARF) over Delhi

The aerosol optical depth (AOD) measurement at 500 nm using MICROTOPS have been compared with the AOD retrieved at 550nm from the MODIS terra satellite measurements and the AOD values were used to model the aerosol radiation forcing (ARF) over Delhi (Fig. 6.13). ARF has been estimated during 2002-2006 using the Santa Barbara DISORT Atmospheric Radiative Transfer model (SBDART). The single scattering albedo (SSA) and the asymmetry parameter used as input in this model have been estimated using the Optical Properties of Aerosol and Cloud (OPAC) model.

Micro Pulse Lidar (MPL) for Atmospheric studies at NPL, New Delhi

Lidar measurements have been proved to be promising tools to enhance our understanding regarding impact of aerosols and clouds on precipitation, radiative processes and climate study. A polarization micro pulse lidar system has been set up and operational (Fig. 6.12) since August 2007 at National Physical Laboratory, New Delhi to perform continuous measurements of aerosols and clouds. The MPL has a capability to monitor range – resolve back-scattered signals from aerosols and clouds at polarizations parallel and perpendicular to the polarization of laser beam.

Studies on trace gases and aerosols at NPL, New Delhi

The trace gases and aerosols play a major role in at least two important areas: climate and air quality. Continuous monitoring for surface ozone, oxides of nitrogen, PM1, PM2.5 and PM10, Methane and Non-methane hydrocarbons, carbon monoxide and aerosols size distribution in 0.3-20μm spectral range were carried out and a reliable and systemic observations data set has been generated. The data set will be helpful to validate regional scale dispersion model and predicating tools to help us build scenarios for future, so that adverse environment effects can be minimized.

Model for forecasting the local time of clearance of fog using ground-based remote atmospheric measurements

A model for computing the local time of clearance of radiative fog, due to the evaporation of liquid water droplets by solar radiation, using groundbased remote atmospheric measurements has been developed. The parameters that need to be measured or estimated are surface air-temperature, temperature inversion-layer thickness, temperature gradient across inversion-layer, aerosol optical depth and liquid water content in fog. Additional parameters that have been input (from models elsewhere) are soil albedo for solar radiation and the reflectance of liquid water droplets for solar radiation.

Mobile communication

In order to improve the rural cellular communication an attempt is made to characterize the radio channel over rural zones along rail roads. This involved development of various prediction tools requiring the comparison of radio measurements with models. For a country like India where diverse terrain conditions exist, same prediction method might not hold well in all the regions. To identify the methods suitable to rural zones an attempt is made to compare the measured results over selected north and West Indian base stations with classical two- ray, Hata and ITM models.