Spatial analysis of aerosol optical depth obtained by air quality modellingand SEVIRI satellite observations over Portugal

Özet

The aim of this work is to explore the aerosol optical depth (AOD) data provided by different sources, namelysatellite observations, air quality modelling and Aerosol Robotic Network (AERONET) observations, in order toimprove characterisation of aerosol spatial distribution and to assess the contribution of the dust events on AODover Portugal. Thus, the spatial and temporal variations of the AOD data were analysed for May 2011 taking intoaccount the occurrence of mineral dust events.Satellite data obtained by Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) instrument and airquality modelling results from the Comprehensive Air Quality Model (CAMx) over Portugal were explored. Inthis work, AOD values with a temporal resolution of 15 min were obtained from SEVIRI. Additionally, 3D datawith 23 vertical layers for each aerosol constituent, size distribution and chemical composition were obtainedfrom the modelling approach and used to compute the AOD at 550 nm by integrating of aerosol extinctioncoefficient (Qext) over the total atmospheric column.Despite the outbreaks of mineral dust occurring during this period, the overall contribution of organic carbon(OC), black carbon (BC) and sulphate (SO4) compounds to the monthly average AOD values estimated by themodel is very important achieving 95% mainly located in the northern part of the studied region. The modeloutputs and SEVIRI data were validated with AERONET observations presenting correlation coefficients of 0.71and 0.68 respectively. Three different modes of aerosol were classified based on Ångström coefficient versusAOD and distinguishing between the dominance offine and coarse aerosol fractions. The analysis implementedreveal that intercomparison of satellite observations with air quality modelling contribute to better under-standing of the discrepancies presented in spatial pattern of AOD.