Abstract
Abstract. Single-particle mixing state information can be a powerful tool for assessing the relative impact of local and regional sources of ambient particulate matter in urban environments. However, quantitative mixing state data are challenging to obtain using single-particle mass spectrometers. In this study, the quantitative chemical composition of carbonaceous single particles has been determined using an aerosol time-of-flight mass spectrometer (ATOFMS) as part of the MEGAPOLI 2010 winter campaign in Paris, France. Relative peak areas of marker ions for elemental carbon (EC), organic aerosol (OA), ammonium, nitrate, sulfate and potassium were compared with concurrent measurements from an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), a thermal–optical OCEC analyser and a particle into liquid sampler coupled with ion chromatography (PILS-IC). ATOFMS-derived estimated mass concentrations reproduced the variability of these species well (R2 = 0.67–0.78), and 10 discrete mixing states for carbonaceous particles were identified and quantified. The chemical mixing state of HR-ToF-AMS organic aerosol factors, resolved using positive matrix factorisation, was also investigated through comparison with the ATOFMS dataset. The results indicate that hydrocarbon-like OA (HOA) detected in Paris is associated with two EC-rich mixing states which differ in their relative sulfate content, while fresh biomass burning OA (BBOA) is associated with two mixing states which differ significantly in their OA / EC ratios. Aged biomass burning OA (OOA2-BBOA) was found to be significantly internally mixed with nitrate, while secondary, oxidised OA (OOA) was associated with five particle mixing states, each exhibiting different relative secondary inorganic ion content. Externally mixed secondary organic aerosol was not observed. These findings demonstrate the range of primary and secondary organic aerosol mixing states in Paris. Examination of the temporal behaviour and chemical composition of the ATOFMS classes also enabled estimation of the relative contribution of transported emissions of each chemical species and total particle mass in the size range investigated. Only 22% of the total ATOFMS-derived particle mass was apportioned to fresh, local emissions, with 78% apportioned to regional/continental-scale emissions.
Highlights
Particulate matter is known to significantly impact air quality in urban environments, and elevated ambient mass concentrations are associated with adverse health effects
The aerosol time-of-flight mass spectrometer (ATOFMS)-derived mass concentration estimates for organic aerosol (OA), elemental carbon (EC) and inorganic ions are compared with data from the HRToF-AMS, PILS and Sunset OCEC analyser in Figs. 1 and 2
EC and OA mass concentrations are slightly overestimated by the ATOFMS, while the inorganic ions are underestimated relative to the other instruments
Summary
Particulate matter is known to significantly impact air quality in urban environments, and elevated ambient mass concentrations are associated with adverse health effects Megacities, defined as metropolitan areas with populations greater than 10 million inhabitants, have been the focus of several large-scale air quality measurement studies in recent years (Molina et al, 2010; Gao et al, 2011; Harrison et al, 2012). While poor air quality in megacities is of serious concern at a local scale, the potential impact of the associated urban plumes on the surrounding regions must be considered. Particulate matter and precursor gas emissions may lead to haze formation or acidic deposition at a regional scale, potentially impacting human health and crop production (Chameides et al, 1994; Molina and Molina, 2004; Lawrence et al, 2007)
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