Solar and interplanetary disturbances that include Interplanetary Coronal Mass Ejections (ICME), Co-rotation Interaction Region (CIR), Solar flares, Solar Energetic Particles (SEP) etc. disturb the earth’s magnetosphere-ionosphere-thermosphere system. The scientific objective of the group is to understand and quantify these impacts and compare these with the quiet conditions.

a. Narrow Spectral Band, Narrow Field-of-view airglow photometer: This class of instruments can identify the signatures of ionospheric electric field and electric density perturbations associated with space weather events like geomagnetic storms and magetospheric substorms by observing nighttime thermospheric airglow emissions in the wavelengths of OI 630.0 nm and 777.4 nm. The instrument is capable of enhancing the signal to noise ratio (SNR) by limiting the spectral bandwidth and bringing out the small variations in the airglow intensity buried in the background by limiting the field of view. This philosophy is now being adopted for space-borne measurements on-board Indian satellites.

b. GPS/GNSS/IRNSS receiver based Total Electron Content (TEC) measurements: Ionosphere over low latitude region is one of the most susceptible regions in terms of radio scintillation. Therefore, it is important to investigate the response of ionospheric TEC corresponding to varying space weather conditions. With this aim in mind, three receivers measure TEC over this region using GPS, GNSS and IRNSS satellite transmissions at multiple frequencies (L1, L5, S band etc.) and are operational in the lab round-the-clock.

c. Langmuir Probe: The lab is also engaged in the design and fabrication of Langmuir probes for space plasma measurements on-board rocket and satellites. The speciality of this class Langmuir Probe is its capability to capture small changes in the electron density perturbations enabling the group to address various plasma irregularity processes in the ionosphere.

A few important results in the recent times include

1. Evidence and characterization of space weather processes using thermospheric airglow emission measurements
2. Identification and quantification of the role of storms amd substorms on low latitude ionospheric electrodynamics
3. Impact of ICME, CIR etc. on the solar wind-magnetosphere-ionosphere system

The uniqueness of the experiments conducted in the lab include: a) Detection of electric field perturbations associated with the space weather processes on the airglow emission over low latitude b) Measurements using Langmuir probe having high frequency sampling capability that enables to characterize small scale plasma turbulences in the ionosphere c) Radio scintillation measurements in the ionosphere using multiple frequencies

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Major Instrument Details: 1. Multi wavelength sun photometer 2. Pyranometer 3. Pyrgeometer 4. Pyrheliometer

The radiative effects of aerosols are measured as well as estimated in solar and longwave regimes.

VOCs are organic compounds which easily evaporate and enter into atmosphere at ordinary (ambient) temperatures. They are numerous and everywhere (but at trace levels; parts per trillion/billion by volume). Alkanes, Alkenes, Alkynes, Aldehydes, Ketones, Alcohols, Aromatics, etc. are important classes of VOCs found in the earth’ atmosphere. VOCs are short-lived due to fast reactions hydroxyl (OH) radicals (known as the detergent of the atmosphere). VOCs are precursors of Ozone (O₃) [Bad Ozone] and aerosols in the atmosphere. VOCs control the oxidation capacity of the troposphere and can increase the lifetime of greenhouse gases (GHGs). Some VOCs like Benzene & Toluene are Harmful for life! Atmospheric VOCs data can be used to study Emission, Transport, Photo-oxidation, Pollution, Climate, Environment.

(1) Proton Transfer Reaction- Time of Flight- Mass Spectrometry (PTR-TOF-MS)-

The PTR-TOF-MS technique is used for the measurements of different VOC compounds present in atmosphere. This instrument consists of three main parts: Ion source, PTR drift tube, and Detector system.  In PTR-TOF-MS, VOC molecules are ionized in the gaseous phase due to transfer of proton (H⁺) from hydronium ion (H₃O⁺). The proton transfer reaction hence takes place for VOCs which have higher proton affinity (PA) than that of water H₂O (691 kJ/mol). This process of VOC ionization by transfer of proton is also known as soft ionization. This is an important way to ionize VOCs as it avoids the large fragmentations which is needed for the identification and accurate quantification of VOC concentration.  The time of flight (TOF) mass spectrometer separates the ions according to their mass to charge ratio (m/z). The PTR-TOF-MS provides the mass spectra of many VOCs in a short time (<1 s). PTR-TOF is a very sensitive technique and used for measurements of trace gases (ppt-ppb levels) in air and provides a high time resolution data. This is India’s first Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-TOF-MS) system.

(2) Thermal Desorption-Gas Chromatography-Flame Ionization Detector/Mass Spectrometer Detector (TD-GC-FID/MSD)- The gas chromatography (GC) technique is regarded as one of the traditional instrumentations and has been extensively used for the measurements of many trace gases (at as low as pptv) present in the atmosphere. In GC, we use capillary column of about 60 m length in which separation of NMHCs takes place based on their adsorption in column. Later, the compounds separately enter in the detector system based on their retention time in column. In PRL, the GC-FID/MSD system which is coupled with a TD is used for the analysis of a class of VOCs known as non-methane hydrocarbons (NMHCs) for which PTR-TOF-MS based measurement is not possible. In TD, the “Ozone Precursor” has been used for the pre-concentration of NMHCs present in air. The detection is obtained in the form of a chromatogram and further analysis provides both identification and quantification of VOCs and other trace gases.

(3) VOC Analyzers-The VOC analyzer provides online gas chromatograph for the analysis and monitoring of trace amounts of C₂-C₁₂ hydrocarbons. Automatic sampling and pre-concentration are done using an adsorbent trap (cryo + sorbent chemicals). Subsequently, concentrated samples are desorbed and injected into a metallic capillary column regulated by a temperature gradient (programmed). The detection of all compounds eluting from the column is performed by using a micro FID detector. The instrument is robust, compact and very low maintenance and offers excellent quality in terms of repeatability, linearity, stability and sensibility (ppt). VOC analyzers are portable and have been used in field experiments at remote places. This setup has been operated during ship-borne campaigns to study the remote atmosphere.

(A) Importance of Anthropogenic, Biogenic and Photochemical Sources of VOCs in India

I. Our research using the most accurate data set of isoprene and monoterpenes (biogenic tracer) from PTR-TOF-MS (high time- and mass- resolutions) has established that the emissions from terrestrial vegetation are important source of many VOCs in the tropical urban regions in India unlike those at higher latitudes.

II. The comprehensive measurements of different types of VOCs such as oxygenated-VOCs (OVOCs), non-methane hydrocarbons (NMHCs) and biogenic-VOCs (BVOCs) is a first attempt to quantify the contributions of primary anthropogenic (fossil + biofuel combustion), biogenic and photochemical (secondary) sources in complex urban air mixture of India. It is shown that a significant increase (up to ~30%) in isoprene (biogenic) and OVOCs (photochemical) during winter to summer transition period.

III. Our work established, for the first time over the Indian regions, that how VOC composition and their O₃ formation efficiency change with season (based on year-long measurements) in polluted urban and remote high altitude site (free troposphere). We have highlighted the roles of reactions of VOCs with OH radical, convective upward transport and advection that resolved why the VOCs exhibit stronger seasonality in tropical India than those at higher latitudes.

IV. We have investigated that how VOC composition (relative abundance of numerous species) changed under foggy, cloudy and clear-sky conditions in the north India (polluted Indo-Gangtic Plain (IGP) and urban sites in western India during the winter season. His work provided the role of VOCs-NOx photochemistry in the reduction of O₃ during foggy days and enhanced O₃ during clear-sky days in polluted IGP region.

V. We determined the "photochemical age" of air mass using very accurate measurements of reactive VOCs helped to understand that how the transformations (mainly photo-oxidation) of primary VOCs during the transport from Indian subcontinent impact the level and photochemical formation of O₃ over surrounding oceanic regions.

(B) Oceanic Emissions of BVOCs and Role of Convection over Northern Indian Ocean

Our work is credited for extremely important results about the impact of monsoon circulations on oceanic emissions of BVOCs and connective downdraft of O₃-rich over the northern Indian Ocean.

I. Our research established that the oceanic emission is a significant source of BVOCs (light alkenes) in marine boundary layer (MBL) of the northern Indian Ocean. In the daytime, mixing ratios of BVOCs in MBL increased by ∼45% during summer monsoon, while values were low and did not depend on local time in winter. This is the first study of ocean-atmosphere exchange process of BVOCs over the northern Indian Ocean.

II. Our experiments over the northern Indian Ocean established that transport from continental sources (mainly anthropogenic) are major sources of reactive VOCs in costal MBL, while emissions from dissolved organic carbon (DOC, related to primary production) in seawaters are important biogenic source in the open ocean.

III. It is revealed that BVOCs in the MBL of Bay of Bengal (BoB) were particularly high during the cyclonic events due to increased exchange rate from DOC in seawaters. This finding has very important implications with regard to BVOC emissions as cyclonic activities are rather frequent and intense over Bay of Bengal.

IV. One of the landmark contributions is to provide the first observational evidence of sudden convective downdrafts of O₃-rich air from the free troposphere into the MBL during cyclonic conditions. In extremely rare observations (globally), spikes in O₃ concentration (up to 26 ppbv) were accompanied by simultaneous dips (by 3-4 K) in temperature. Thus far, such sharp changes in O₃ due to convective-downdrafts are not reported neither over the land nor over the ocean as downdrafts events are extremely rare to capture due to sporadic nature.

Our Laboratory is the first in India to start the comprehensive measurements of VOCs in different regions of India since year 1998. PRL established India’s first Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-TOF-MS) and Thermal Desorption-Gas Chromatography-Flame Ionization Detector (TD-GC-FID) and Cryo-Trap GC-FID. PRL leads a network VOC compounds (~40 species using PTR-TOF-MS, ~20 species using TD/Cryo-GC-FID, C2-C12 Analyser) in different regions of India under ISRO-GBP.