Aircraft Measurement


Black carbon (BC) aerosols are strong absorber of the solar radiation in the visible and near-infrared wavelengths contributing significantly to positive radiative forcing. During a extensive aerosol field campaign as part of ISRO-GBP program, aircraft measurements of vertical profiles of aerosol black carbon (BC) were made during winter, for the first time, at Kanpur, an urban industrial location in Northern India.

BC was measured by the Aethalometer from Magee Scientific, Berkeley, USA. The instrument was operated at a flow rate of 6.5 liters/min and at an average time base of 1–3 min depending upon the experiment. Athelometer was kept inside the aircraft and its inlet was exposed to the atmosphere by fixing it to the left wing of the aircraft during flight observation. Unpressurised high wing light airplane manufactured by M/s Piper Aircraft Corporation, USA, has been used for the experiments. It is a part of fleet at IIT Kanpur. Aircraft was flown up to 2000 m in the present experiments due to safety reasons. Measurements have been taken continuously from 10 minutes before the take off of the aircraft and continued up to 10 minutes after its landing. Temperature and BC measurements were made simultaneously and the coordinate of each BC measurement has been measured with a hand-held Global Positioning System (GPS) receiver during the experiment.


Two vertical profiling from the same day (morning and afternoon) of BC showed that BC decreases with height up to 600 m and then increases up to 900 m before becoming more or less constant with height. Potential temperature profile, derived from concurrent measurements of temperature, shows a stable layer at the same altitude where BC shows increased concentration. This vertical structure of boundary layer was further confirmed by separate temperature and relative humidity profiles obtained from balloonsondes during December. The increased BC at 900 m suggests the presence of enhanced BC layer, which will have significant implications to BC radiative forcing and modifying cloud properties.

Figure a)Vertical profiles of BC concentration and (b) vertical profiles of temperature (T) and potential temperature (q). The error bars represent ±1 standard deviation of the corresponding measurements.  

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