Study of vertically resolved aerosol properties over an urban background site in Madrid (Spain)

This work presents a comparison of aerosol properties measured by in situ and remote-sensing instrumentation over an urban background site in Madrid (Spain) in autumn 2010. Aerosol size distribution was characterized at ground level by the combined use of two instruments and also in elevated layers by airborne in situ instrumentation. Simultaneously, vertically resolved lidar profiles provided information about the optical properties of aerosols present in the different layers observed. Backscatter-derived Ångström exponent, calculated using Mie theory with volume size distribution detected experimentally, yielded values lower than 0.5 near ground level, increasing to over 1.5 in elevated layers. The same trend was observed for values obtained using the lidar system. Size distribution measured at elevated layers indicated that the large exponents observed there are associated with size distribution, with a negligible contribution of coarse particles. The results are compromised by the major uncertainty associated with the backscatter-derived Ångström exponents, due to the low aerosol load detected in the elevated layers.