Near-infrared laser desorption/ionization aerosol mass spectrometry for measuring organic aerosol at atmospherically relevant aerosol mass loadings

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 aluminium probe and 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]<sup>−</sup>. 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<sup>−3</sup> 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<sup>−3</sup>. 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 SOA fluxes and to aid in remediating the discrepancy between modeled and observed atmospheric total SOA production rates and concentrations

Soft Ionization Chemical Analysis of Secondary Organic Aerosol from Green Leaf Volatiles Emitted by Turf Grass

“…Details for alignment of the particle beam to the Al probe are described elsewhere. 39,43 Typical aerosol masses sampled were in the range of 1−20 ng. Following particle collection, desorption and ionization were performed by a single 1064 nm laser pulse (5 ns) from a Nd:YAG laser (Brio, Quantel USA, Big Sky, CO) and a time-of-flight mass spectrometer was used for chemical analysis.…”

“…Direct online soft ionization aerosol mass spectrometry (AMS) is a sensitive technique to assess SOA formation at a molecular level. , In this study we use metal-assisted near-infrared laser desorption/ionization (NIR-LDI) AMS , to characterize SOA generated from dominant GLVs, their mixtures, and GLVs directly emitted from grass clippings. Recently, Harvey et al identified dominant GLVs from headspace analysis of grass clippings and quantified their relative emission rates.…”

Optical Properties of Secondary Organic Aerosol from cis-3-Hexenol and cis-3-Hexenyl Acetate: Effect of Chemical Composition, Humidity, and Phase

“…Bulk chemical properties (O:C, H:C) were measured using an Aerodyne high-resolution timeof-flight mass spectrometer (HR-ToF-AMS), 28,29 according to Chen et al 30 Molecular-level chemical analysis of SOA was performed using near-IR laser desorption/ionization aerosol mass spectrometry (NIR-LDI-AMS). 31,32 A brief description of NIR-LDI-AMS can be found in the Supporting Information.…”

“…The relative intensities of these bands in the two GLV-SOA systems suggest that CHA-SOA contains a greater fraction of carbonyl moieties than HXL-SOA. Using NIR-LDI-AMS, 31,32 the relative abundance of these species was compared between chemical systems. By summing the area of each spectral peak corresponding to carbonyl-containing species (as identified by Jain et al 39 ) and normalizing to the total area of the mass spectrum, the "carbonyl contribution" to CHA-SOA (3.7 ± 0.8%) was found to be statistically greater than that of HXL-SOA (2.1 ± 0.5%).…”

Real-Time Analysis of Ambient Organic Aerosols Using Aerosol Flowing Atmospheric-Pressure Afterglow Mass Spectrometry (AeroFAPA-MS)

“…9 Therefore, recent instrumental developments focus on softer ionization techniques such as atmospheric pressure chemical ionization (APCI-MS), 11,12 extractive electrospray ionization (EESI-MS), 13 or near-infrared (IR) laser desorption ionization. 14 Yet unexplored in aerosol research are the latest developments in soft ionization techniques that have been made during the advent of ambient desorption/ionization mass spectrometry (ADI-MS). The newly developed ionization techniques comprise ion sources such as the low temperature plasma probe (LTP), 15 the DART source, 16 the flowing atmosphericpressure afterglow (FAPA) source, 17 or the desorption electrospray ionization (DESI) source.…”