Monitoring of inorganic ions, carbonaceous matter and mass in ambient aerosol particles with online and offline methods

摘要

Year-long high timeresolution measurements of major chemical components inatmospheric sub-micrometer particles were conducted at an urban backgroundstation in Finland 2006–2007. Ions were analyzed using aparticle-into-liquid sampler combined with an ion chromatograph (PILS-IC),organic and elemental carbon (OC and EC) by using a semicontinuos OC/ECaerosol carbon analyzer (RT-OCEC), and PM mass with a taperedelement oscillating microbalance (TEOM). Long time series providesinformation on differences between the used measurement techniques as wellas information about the diurnal and seasonal changes. Chemical mass closurewas constructed by comparing the identified aerosol mass with the measuredPM. The sum of all components measured online (ions, particulateorganic matter (POM), EC) represented only 65% of the total PM mass. The difference can be explained by the difference in cutoff sizes(PM for online measurements, PM for total mass) and byevaporation of the semivolatile/volatile components. In general, somedifferences in results were observed when the results of thecontinuous/semicontinuous instruments were compared with those of theconventional filter samplings. For non-volatile compounds, like sulfate andpotassium, correlation between the filter samples and the PILS was good butgreater differences were observed for the semivolatile compounds likenitrate and ammonium. For OC the results of the RT-OCEC were on average10% larger than those of the filters. When compared to filtermeasurements, high resolution measurements provide important data on shortpollution plumes as well as on diurnal changes. Clear seasonal and diurnalcycles were observed for nitrate and EC.