Lower Troposphere Observation over Urban Area with Lidar at 1064？nm

An episode of relatively thick (till 3？km) aerosol formation over the urban area of Sofia city was observed by lidar at a wavelength of 1064？nm. The lidar is part of Sofia lidar station at the Institute of Electronics of Bulgarian Academy of Sciences. Analysis of the weather conditions during the measurement period explains the stable persistence of such formation of human-activity aerosol over the town for the days of observation 20, 21, 23, and 24 June, 2011. The estimated top of the Planetary Boundary Layer for the measurement dated 23 June showed unusually high altitude 2200？m above ground. The results are presented in terms of vertical atmospheric backscatter coefficient profiles and color maps of the aerosol stratification evolution. 1. Introduction Aerosols are of central importance for global climate, atmospheric chemistry and physics, hydrological cycle and biosphere, ecosystems, and public health. Due to their short lifetime and strong tropospheric interactions, their global concentrations and properties are poorly known [1]. Aerosol particles affect atmospheric radiation and cloud microphysics and are considered a major uncertainty in climate changes. The term “atmospheric aerosol” encompasses a wide range of particle types having different compositions, sizes, shapes, and optical properties. Aerosols may be liquid or solid particles suspended in the air with typical diameters ranging over four orders of magnitude (approximately from a few nanometers to a few tens of micrometers). They consist of inorganic and organic components and varying amounts of water. Atmospheric particles are emitted from a variety of natural and human processes. On a global basis, the bulk of aerosols originate from natural sources, mainly sea salt, desert and soil dust, wildfire smoke, and volcanic ash [2, 3]. At present, the quantity of anthropogenic emissions increases with alarming speed. This is associated with a growing economy, rapid urban expansion, increasing rate of motorization, expanding industrial activity, and so forth. Human-produced particles can be dominant form of aerosol in highly populated and industrialized regions and in areas of intense agricultural burning. They are also tightly linked to problems of visibility reduction, acid rain, and smog in many industrial areas of the world. Anthropogenic aerosols are transported by prevailing winds, and the elements contained in them are redeposited often on the surface of the Earth far away from the location that they were produced [4–8]. The natural background aerosol is present in the absence of human