Thorsten Hohaus

Aerosol Mass Spectrometric Features of Biogenic SOA: Observations from a Plant Chamber and in Rural Atmospheric Environments

Secondary organic aerosol (SOA) is known to form from a variety of anthropogenic and biogenic precursors. Current estimates of global SOA production vary over 2 orders of magnitude. Since no direct measurement technique for SOA exists, quantifying SOA remains a challenge for atmospheric studies. The identification of biogenic SOA (BSOA) based on mass spectral signatures offers the possibility to derive source information of organic aerosol (OA) with high time resolution. Here we present data from simulation experiments. The BSOA from tree emissions was characterized with an Aerodyne quadrupole aerosol mass spectrometer (Q-AMS). Collection efficiencies were close to 1, and effective densities of the BSOA were found to be 1.3 +/- 0.1 g/cm(3). The mass spectra of SOA from different trees were found to be highly similar. The average BSOA mass spectrum from tree emissions is compared to a BSOA component spectrum extracted from field data. It is shown that overall the spectra agree well and that the mass spectral features of BSOA are distinctively different from those of OA components related to fresh fossil fuel and biomass combustions. The simulation chamber mass spectrum may potentially be useful for the identification and interpretation of biogenic SOA components in ambient data sets.

Stable carbon isotope composition of secondary organic aerosol from β‐pinene oxidation

[1] A chamber study was carried out to investigate the stable carbon isotopic composition (δ 13 C) of secondary organic aerosol (SOA) formed from ozonolysis of β-pinene. β-Pinene (600 ppb) with a known δ 13 C value (-30.1%‰) and 500 ppb ozone were injected into the chamber in the absence of light and the resulting SOA was collected on preheated quartz fiber filters. Furthermore, δ 13 C values of the gas-phase β-pinene and one of its oxidation products, nopinone, were measured using a gas chromatograph coupled to an isotope ratio mass spectrometer (GC-IRMS). β-Pinene was progressively enriched with the heavy carbon isotope due to the kinetic isotope effect (KIE). The KIE of the reaction of β-pinene with ozone was measured to be 1.0026 ( O3 e 2.6 ± 1.5%o). The δ 13 C value of total secondary organic aerosol was very similar to that of its precursor (average = -29.6 ± 0.2%o) independent of experiment time. Nopinone, one of the major oxidation products of β-pinene, was found in both the gas and aerosol phases. The gas-phase nopinone was heavier than the initial β-pinene by 1.3%o but lighter than the corresponding aerosol-phase nopinone. On average, the gas-phase nopinone was lighter by 2.3‰ than the corresponding aerosol-phase nopinone. The second product found in the SOA was detected as acetone, but it desorbed from the filter at a higher temperature than nopinone, which indicates that it is a pyrolysis product. The acetone showed a much lower δ 13 C (-36.6‰) compared to the initial β-pinene δ 13 C.

Development of a volatility and polarity separator (VAPS) for volatility- and polarity-resolved organic aerosol measurement

ABSTRACT Discrepancies between modeled and measured atmospheric organic aerosol (OA) have highlighted the need for in situ instrumentation to better characterize the sources, formation mechanisms, and atmospheric evolution of ambient OA. We have developed the Volatility and Polarity Separator (VAPS) for hourly measurements of volatility- and polarity-resolved OA detected using high-resolution time-of-flight mass spectrometry (HR-ToF-MS). Here, atmospheric OA is inertially impacted onto a collection cell, material is transferred onto a short transfer line located inside a gas chromatography (GC) oven, the oven is heated to provide a first-dimension separation of volatility, then thermally pulsed through a short polar GC column for a second-dimension polarity separation, and finally detected by HR-ToF-MS. This novel instrument increases the mass throughput of ambient OA in comparison to traditional GC due to shorter transfer paths and passivated coatings. Molecular separation resolution is partially sacrificed for this increased mass recovery, but the high-resolution mass spectral data recovers information such as chemical classes and even some individual compounds along with elemental composition to determine aerosol oxidation states. Different techniques for interpreting and representing VAPS data are considered and its applicability to positive matrix factorization (PMF) analysis is demonstrated. Copyright

Aerosol Formation from Plant Emissions: The Jülich Plant Chamber Experiments

We have performed measurements of particle formation and growth in a setup consisting of a plant and a reaction chamber, using live plants as well as an α-pinene source. The nucleation rates observed varied between 0.04 and 260 cm �3 s �1 , while the growth rates were 10-30 nm/h. We found that the formation and growth rates of particles increased with increasing amounts of carbon emitted by the plants, but there was significant variation between the plants. We have also modeled the formation of the aerosol using a continuously stirred tank reactor concept, and found that the basic physics and chemistry of the chamber are captured well.