Sampling From The Air
Samples of the air at different altitudes above different parts of the Earth can be collected and analysed to monitor the effects of the environment or the activities of humans on the atmosphere. Relatively long lifetime compounds such as CO2 can be collected and analysed easily but more reactive species such as the hydroxyl radical (ĽOH) or aerosols require a more imaginative approach.
An example of an aerosol spectrometer probe mounted on an aircraft.
Taken from: http://www.weathermod.com
The hydroxyl radical is formed by a photochemical reaction and is key in the oxidation and effective elimination of harmful pollutants and greenhouse gases. The ĽOH must have passed into the chamber through the air inlet without hitting any surfaces and terminating the radical. The air inlet is mounted on an aircraft and flown through the collection zone and then the concentration examined by reading the fluorescence fingerprint after excitation by a UV laser.
The range of these measurements is limited by the altitude the plane carrying the equipment can reach. An alternative approach is to mount spectrometers on balloons and release them into the atmosphere, however, the flight path cannot be controlled as the balloons are unpowered.
Deployment of a balloon equipped with sensing instruments.
Taken from: http://science.jpl.nasa.gov/
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