Investigating the Effect of Tropical Cyclones on Atmospheric Chemistry in the Upper Troposphere

&amp;lt;p&amp;gt;Tropical cyclones (TCs) containing widespread and intense convection, play a dominant role in stratosphere-troposphere exchange (STE) processes in the upper troposphere and lower stratosphere (UTLS) region. Here we examine the variation of meteorological and chemical fields associated with two different pre-monsoon tropical cyclones: MORA and FANI, by combining satellite-based observations from AIRS (The Atmospheric Infrared Sounder ) and different model reanalysis datasets from ERA5 (fifth generation of ECMWF atmospheric reanalyses), CAMS (Copernicus Atmosphere Monitoring Service), MERRA-2 (The Modern-Era Retrospective analysis for Research and Applications, Version 2), and NCEP (National Centers for Environmental Prediction). An increase in the upper-tropospheric ozone (O&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;) by 15&amp;amp;#8211; 30 ppbv is observed over the Bay of Bengal during the high phase of MORA cyclone. Intrusion of O&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; from lower stratosphere to upper troposphere is clearly observed from 50 to 300 hPa during the cyclonic period, contributing enhancement in the upper tropospheric O&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;. There are no such indication of enhanced O&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; values before and after the dissipation of MORA cyclone. General behavior of intrusion associated with severe MORA cyclone is well captured by all the models and satellite, however some differences are seen in the intensity and structure of the STE events. Strong updrafts and downdrafts present in the vicinity of tropopause during TC passage weakened the stability of tropopause layer. The low tropopause temperature with enhanced potential vorticity (PV) feature extended vertically downward from lower stratosphere to troposphere confirms the stratosphere to tropospheric intrusion during the cyclonic period. Concurrently, low relative humidity (RH) along with negative RH-O&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; correlation during the overhead cyclone further supports the intrusion. Contrarily, satellite and model results revealed no significant variation in O&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; mixing ratio in the lower stratosphere down to the tropopause level during the high phase of extremely severe FANI cyclone. Strong convective activity during the passage of FANI confirms the upward propagation of CO rich (O&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; poor) air masses from surface to the mid/upper troposphere. The air masses are then trapped by anticyclone around the tropopause levels. This study clearly reveals that tropical cyclones play major role in exchanges of mass and energy between the stratosphere and troposphere (and vice versa) besides being general weather phenomena.&amp;lt;/p&amp;gt;</jats:p

Short term introduction of pollutants into the atmosphere at a location in the Brahmaputra Basin: A case study

AbstractIntensive fire ignition and cracker work activities takes place during the festival of light called Diwali in India, celebrated for a period of few days in the month of October or November every year. The firecracker releases several pollutants [such as particulate matter (PM), black carbon (BC), organics, trace gases] near the surface. The effect of firecrackers on the atmospheric constituents is evaluated over Dibrugarh by monitoring the concentrations of PM, PM10 (particle radius ≤10 µm), PM2.5 (particle radius ≤2.5 µm) and BC during the Diwali and post-Diwali days (5 days after the Diwali Festival) in the years 2009 and 2010. Monthly average concentrations of each species except for the Diwali and post Diwali days is considered as the background concentrations. The concentration levels of the pollutants as recorded on the Diwali days are found to be a number of times higher (5.33 and 2.50 times for PM10, 5.74 and 2.65 times for PM2.5, 1.21 and 1.66 times for BC for the year 2009 and 2010, respectively) than the background levels at the peak hours of the fire work activity. To delineate the contribution of fireworks to the high concentrations of the species we performed air mass back trajectory analysis using the NOAA–HYSPLIT model in order to examine the existence of the transported aerosols. The ten day accumulated MODIS fire maps are also analyzed to mark out the contribution of aerosols from biomass burning. These analyses reveal that the higher concentrations of near surface aerosols including BC during the festival is due to the local effect of firework activities, neither because of long–range transport nor due to biomass burning activities. However, the higher concentration of pollutants for short periods has not degraded air quality substantially to cause health risks to people exposed to the festival in this environment