Organic aerosol source apportionment in Zurich using an extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF-MS) – Part 1: Biogenic influences and day–night chemistry in summer

Abstract

Abstract. Improving the understanding of the health and climate impacts of aerosols remains challenging and is restricted by the limitations of current measurement techniques. Detailed investigation of secondary organic aerosol (SOA), which is typically the dominating fraction of the organic aerosol (OA), requires instrumentation capable of real-time, in situ measurements of molecular composition. In this study, we present the first ambient measurements by a novel extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF-MS). The EESI-TOF-MS was deployed along with a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) during summer 2016 at an urban location (Zurich, Switzerland). Positive matrix factorization (PMF), implemented within the Multilinear Engine (ME-2), was applied to the data from both instruments to quantify the primary and secondary contributions to OA. From the EESI-TOF-MS analysis, a six-factor solution was selected as the most representative and interpretable solution for the investigated dataset, including two primary and four secondary factors. The primary factors are dominated by cooking and cigarette smoke signatures while the secondary factors are discriminated according to their daytime (two factors) and night-time (two factors) chemistry. All four factors showed strong influence by biogenic emissions but exhibited significant day–night differences. Factors dominating during daytime showed predominantly ions characteristic of monoterpene and sesquiterpene oxidation while the night-time factors included less oxygenated terpene oxidation products, as well as organonitrates which were likely derived from NO3 radical oxidation of monoterpenes. Overall, the signal measured by the EESI-TOF-MS and AMS showed a good correlation. Further, the two instruments were in excellent agreement in terms of both the mass contribution apportioned to the sum of POA and SOA factors and the total SOA signal. However, while the oxygenated organic aerosol (OOA) factors separated by AMS analysis exhibited a flat diurnal pattern, the EESI-TOF-MS factors illustrated significant chemical variation throughout the day. The captured variability, inaccessible from AMS PMF analysis, was shown to be consistent with the variations in the physiochemical processes influencing chemical composition and SOA formation. The improved source separation and interpretability of EESI-TOF-MS results suggest it to be a promising approach to source apportionment and atmospheric composition research.

Long-term sub-micrometer aerosol chemical composition in the boreal forest: inter- and intra-annual variability

“…The instrument was calibrated every 2-4 weeks using three different VOC standards (Apel-Riemer), and the instrumental background was measured every third hour using VOCfree air produced by a zero air generator (Parker Chrom-Gas, model 3501). Normalized sensitivities and the volume mixing ratios were then calculated using the method introduced previously (Taipale et al, 2008). For example, the normalized sensitivity of α-pinene (measured at m/Q 137 Th) varied between 2 and 5 n.c.p.s.…”

“…5a. Such behavior in organic aerosol loading is often attributed to biogenic SOA formation from BVOCs (Daellenbach et al, 2017;Stefenelli et al, 2019;Vlachou et al, 2018;Paasonen et al, 2013).…”

Fossil fuel combustion, biomass burning and biogenic sources of fine carbonaceous aerosol in the Carpathian Basin

“…2, 3 and 4, respectively. The PM 2.5 mass represents the bulk fine PM; EC is a typical primary aerosol constituent, while WSOC expresses mainly SOA and partially BB products (which also exhibit substantial hygroscopicity and thus water-solubility; Swietlicki et al, 2008). These species are rather different as far as their sources are concerned.…”

“…This can be explained by intensive BB in the area with respect to the other environments (Sect. 3.5) and with the fact that BB particles possess relatively high hygroscopicity (Swietlicki et al, 2008) and water solubility. In the remaining two months, the shares of the WSOC were similar to each other and varied without an obvious tendency.…”

“…They include (1) source-specific marker methods (Fraser and Lakshmanan, 2000;Szidat et al, 2006Szidat et al, , 2009Minguillón et al, 2011;Zhang et al, 2012;Bernardoni et al, 2013), (2) multiwavelength optical methods (Sandradewi et al, 2008a, b;Zotter et al, 2017) and (3) various multivariate statistical methods based on online or offline data (Hopke, 2016;Maenhaut et al, 2016). Recently, the third approach also takes advantage of dedicated molecular tracers or fragments from mass spectrometry or advanced optical techniques (Forello et al, 2019;Stefenelli et al, 2019).…”