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Radiometric observations of relative humidity profile at Kolkata show a significant fall at around 1 to 2 km height during convective rain events. An extensive investigation shows that the fall of relative humidity is not seen during calm conditions but is strongly related to the characteristics of temperature lapse rate profiles. Moreover, the phenomenon may have strong association with boundary layer structure. The reason for such anomalies in the planetary boundary layer humidity profile might be due to the release of latent heat at the mentioned altitude. The abundance of pollutant aerosols in urban regions has also been found to contribute to this relative humidity anomaly. It has also been reported that this boundary layer relative humidity is accompanied by high latent heat release and condensation of vapour to liquid which is not much prominent in other rain types as observed in stratiform rain. Hence, convective rain produces some unique boundary layer characteristics which have also been partially supported with allied satellite and multi-station observations. [ABSTRACT FROM AUTHOR]

Near surface aerosol black carbon (BC) concentration data were collected using a seven channel Aethalometer (AE31) during June 2012–May 2013 in Kolkata (22° 34′E, 88° 22′N), a metropolitan city located near the land–ocean boundary in Eastern India. BC concentration shows a prominent seasonal and diurnal variation associated with the meteorological parameters. The mean BC concentration varied from 5 μg/m 3 to 27 μg/m 3 seasonally. The variation of BC mass concentration and its significant association with atmospheric parameters such as temperature profile, relative humidity and wind speed have been studied. Moreover, the influence of the transported air masses on BC concentration at different seasons has also been discussed. An estimation of Angstrom exponent discloses that fossil fuel combustion is a major source of BC at this location. [ABSTRACT FROM AUTHOR]

Atmospheric pollutants (NO 2 , SO 2 , PM10, BC, CO, surface O 3 ), emitted during fireworks display, have significant effects on meteorological parameters like air temperature, relative humidity, lapse rate and visibility in air over Kolkata (22°65′ N, 88°45′ E), a metropolitan city near the land–ocean boundary, on the eve of Deepawali festival when extensive fireworks are burnt. Long-term trend (2005–2013), indicates that the yearly average concentrations of both primary and secondary air pollutants have increased, exceeding the National Ambient Air Quality Standard (NAAQS) limit, on the respective Deepawali days. Short-term study (2012–2013) during the festival shows that the average pollutant concentrations have increased too compared to normal days. This study also reveals the immediate effects of the increased air pollutants on the boundary layer meteorology. PM10 has been found to be the most dominant atmospheric pollutants during this period. As a result of an increase in atmospheric heat content with elevated surface air temperature, a significant increase in the environmental lapse rate bears a signature of the influence of pollutants on the boundary layer temperature profile. A change in the diurnal pattern of relative humidity as well as in the vertical temperature profile is due to the change of the lapse rate during the festival days. Thus, the atmospheric pollutants during this festival over the urban region have significant effect on the boundary layer meteorology with bearings on environmental hazards. [ABSTRACT FROM AUTHOR]