Summertine re-circulations of air pollutans over the north-eastern Iberian coast observed from systematic EARLINET lidar measurements in Barcelona

Abstract

Regular aerosol backscatter measurements using an elastic-backscatter lidar were performed from May 2000 to December 2002 in Barcelona (Spain) in the frame of EU EARLINET Project (European Aerosol Research Lidar Network). Vertical profiles retrievedin a regular schedule confirmedthe presence of multiple aerosol layers of regional origin above the mixing layer during numerous measurement days. Analysis of the meteorological situation of the corresponding days showed common synoptic regimes, which are typical in summertime around the region. As documented by earlier studies, under strong insolation and weak synoptic forcing, sea breezes and mountain-induced winds develop to create re-circulations of pollutants along the eastern Iberian coast. Layers are formed when aerosols are injectedfrom the mountains into the return flow at various heights andd istances from the coast. Aerosol layers can be foundabove the mixing layer up to 4000m with variable thickness typically rangedbetween 100 and1000 m. The mixing height mainly oscillates between 400 and 800m asl in periods of maximum insolation. Four selected episodes are analysed combining lidar profiles, radiosoundings and synoptic meteorology information. One of them includes regional re-circulation aerosols at low levels andupper Saharan dust layers. Maximum backscatter coefficients ranged from 1 10 6 to 2 10 6 (m sr) 1 at the wavelength of 1064 nm. Assuming a lidar ratio of 30 sr (60 sr for Saharan dust), aerosol optical depths above the mixing layer ranged from 0.016 to 0.073. Detailed mesoscale analysis of one episode is performed by means of high resolution modelling with the PSU/NCAR Mesoscale Model 5 (MM5).