Urban aerosol detection with the Vaisala ceilometer

Vaisala CT25K ceilometer is a backscatter lidar that is designed particularly for cloud base detection. Detecting the lower troposphere aerosols offers a technological challenge for the ceilometer. Due to the single-lens optical design concept CT25K is able to receive the backscatter signal also from very low altitudes. By making some software modifications to the off-the-shelf product we were able to detect urban aerosols. The data from test site close to a large urban area and from Vaisala Oyj's own test field in Helsinki show that even a small lidar is capable of detecting aerosols also in daytime. These results give insight into the behavior of mixing layer in urban environment. The results also show that the signal to noise ratio of this commercial instrument is sufficient for detection of aerosol layers in a variety of meteorological conditions.