Understanding of atmospheric aerosol particles with improved particle identification and quantification by single particle mass spectrometry

Single particle mass spectrometry (SPMS) is a useful, albeit not fully quantitative tool to determine chemical composition and mixing state of aerosol particles in the atmosphere. During a six-week field campaign in summer 2016 at a rural site in the upper Rhine valley near Karlsruhe city in southwest Germany, ~3.7 × 10⁵ single particles were analysed by a laser ablation aerosol particle time-of-flight mass spectrometer (LAAPTOF). Combining fuzzy classification, marker peaks, typical peak ratios, and laboratory-based reference spectra, seven major particle classes were identified. With the precise identification and well characterized overall detection efficiency (ODE) for this instrument, particle similarity can be transferred into corrected number fractions and further transferred into mass fractions. Considering the entire measurement period, “Potassium rich and aromatics coated dust” (class 5) dominated the particle number (46.5% number fraction) and mass (36.0% mass fraction); “Sodium salts like particles” (class 3) were the second lowest in number (3.5%), but the second dominating class in terms of particle mass (25.3%). This difference demonstrates the crucial role of particle mass quantification for SPMS data. ... mehrUsing corrections for maximum, mean, and minimum ODE, the total mass of the quantified particles measured by LAAPTOF accounts for ~12%, ~25%, and ~104% of the total mass measured by an aerosol mass spectrometer (AMS) with a collection efficiency of 0.5. These two mass spectrometers show a good correlation (correlation coefficient γ > 0.6) regarding total mass for more than 70% of the measurement time, indicating non-refractory species measured by AMS might originate from particles consisting of internally mixed non-refractory and refractory components. In addition, specific relationships of LAAPTOF ion intensities and AMS mass concentrations for non-refractory compounds were found for specific measurement periods. Furthermore, our approach allows for the first time to assign the nonrefractory compounds measured by AMS to different particle classes. Overall AMS-nitrate was mainly arising from class 3, while class 5 was dominant during events rich in organic aerosol particles.