Abstract
Abstract. A new method, near-infrared laser desorption/ionization aerosol mass spectrometry (NIR-LDI-AMS), is described for the real time analysis of organic aerosols at atmospherically relevant total mass loadings. Particles are sampled with an aerodynamic lens onto an aluminum probe. A moderate energy NIR laser pulse at 1064 nm is directed onto the probe to vaporize and ionize particle components. Delayed pulse extraction is then used to sample the ions into a reflectron time of flight mass spectrometer for chemical analysis. The soft ionization afforded by the NIR photons results in minimal fragmentation (loss of a hydrogen atom) producing intact pseudo-molecular anions at [M-H]−. The limit of detection measured for pure oleic acid particles (geometric mean diameter and standard deviation of 180 nm and 1.3, respectively) was 140 fg (or 1.7 ng m−3 per minute sampling time). As an example of the utility of NIR-LDI-AMS to measurements of atmospheric importance, the method was applied to laboratory chamber measurements of the secondary organic aerosol formation from ozonolysis of α-pinene. High quality mass spectra were recorded with a 2-min time resolution for total aerosol mass loadings ranging from 1.5 to 8.7 μg m−3. These results demonstrate the potential of NIR-LDI-AMS to allow for more accurate measurements of the organic fraction of atmospheric particulate at realistic mass loadings. Measurements at ambient-levels of SOA mass loading are important to improve parameterizations of chamber-based SOA formation for modeling regional and global SOA fluxes and to aid in remediating the discrepancy between modeled and observed atmospheric total SOA production rates and concentrations.
Highlights
Atmospheric aerosols have an important role in many atmospheric and environmental processes; exerting an influence on global and regional radiative energy balance, visibility, atmospheric circulation, the hydrological cycle, the regulation of greenhouse and reactive gases, and human health (Kanakidou et al, 2005; Poschl, 2005; Seinfeld and Pankow, 2003)
As discussed in a recent review on Secondary organic aerosols (SOA) (Hallquist et al, 2009), bottom-up estimates of global SOA production give total biogenic SOA fluxes of 12–70 Tg yr−1, and somewhat lower fluxes for anthropogenic SOA. These combine volatile organic compound (VOC) fluxes with laboratory-derived data and typically estimate global SOA fluxes at about one to two orders lower than values derived from top-down estimates, which are based in part on constraining the atmospheric fate of VOC precursors to SOA
The discrepancy in estimating global SOA fluxes between these two approaches highlights the need for a better understanding of the oxidative transformation of VOC precursors to SOA and the gasto-particle partitioning of these oxidation reaction products
Summary
Atmospheric aerosols have an important role in many atmospheric and environmental processes; exerting an influence on global and regional radiative energy balance, visibility, atmospheric circulation, the hydrological cycle, the regulation of greenhouse and reactive gases, and human health (Kanakidou et al, 2005; Poschl, 2005; Seinfeld and Pankow, 2003). PTR-MS has been adapted to the measurement of particulate phase organics, for real-time chamber-based studies, albeit at high COA (Hellen et al, 2008), and very recently for organic particles collected from both chamberbased studies and field observations (Holzinger et al, 2010) by combining PTR-MS with a collection-thermal-desorption (TD) aerosol sampling technique In this latter study, the reported detection limit of aerosol compounds was 35 pg (or 0.2 ng m−3 for a reported aerosol collection time of approximately three hours) (Holzinger et al, 2010) making TDPTR-MS a potentially powerful tool for the characterization of SOA at low total organic mass loadings. The high sensitivity we have observed coupled to the minimal fragmentation of these species makes it an ideal method for the analysis of complex, multicomponent organic particles, including SOA particles
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
