John W. Grossenbacher

Implementation of DART and DESI ionization on a fieldable mass spectrometer.

A recently developed prototype mobile laboratory mass spectrometer, incorporating an atmospheric pressure ionization (API) interface, is described. This system takes advantage of the small size, lower voltage requirements, and tandem MS abilities of the cylindrical ion trap mass analyzer. The prototype API MS uses small, low-power pumps to fit into a 0.1-m3 self-contained package weighing <45 kg. This instrument has been adapted to allow rapid interfacing to electrospray ionization, desorption electrospray ionization, and direct analysis in real-time sources. Initial data indicate that these techniques provide rapid detection and identification of compounds for quality control, homeland security, and forensic applications. In addition, this instrument is self-contained and compact, making it ideally extensible to mobile laboratory and field analyses. Initial MS and MS/MS data for analyses of drugs, food, and explosives are presented herein.

Observations of reactive oxidized nitrogen and speciation of NO y during the PROPHET summer 1998 intensive

Measurements of NO y , NO x , PAN, PPN, MPAN, C 3 -C 5 alkyl nitrates, total isoprene nitrates, HNO 3 , HONO, and aerosol NO 3 - and NO 2 - were made during the summer 1998 intensive of the Program for Research on Oxidants: Photochemistry, Emissions, and Transport (PROPHET). Mixing ratios of NO y , NO x , PAN, PPN, and alkyl nitrates were observed to have a strong dependence on the direction of transport to the site as was expected from the distribution of major urban and industrial sources. A peak in NO x and NO x /NO y during the morning in southerly flow provides evidence for the transport of relatively unprocessed emissions in layers above the nocturnal boundary layer. The difference in PAN and PPN levels between north and south flow directions indicates a net transport of reactive nitrogen to regions farther north. Isoprene nitrates were observed to typically comprise less than 1% of NO y in spite of the dominance of isoprene in local VOC chemistry, although due to the rapid losses of isoprene nitrates through reaction, vertical mixing, and deposition, their role in the processing of NO y may be significant. General agreement was observed between NO y and the sum of the individually measured constituents during ten 24 hour periods, although a linear regression indicates the potential for an interference in the individual measurements and a possible shortfall in NO y . Measurements indicate that HONO may play a larger role in the reactive nitrogen budget than previously expected for a rural site. HONO/NO 2 for a 24 hour period was observed to be 0.09-0.25 and suggests the likelihood of a significant heterogeneous production pathway or pathways.

Measurements of isoprene nitrates above a forest canopy

Measurements of atmospheric organic nitrates derived from isoprene, i.e., “isoprene nitrates”, were conducted from July 14 to August 19, 1998, as part of the 1998 summer intensive measurement campaign of the Program for Research on Oxidants: PHotochemistry, Emissions, and Transport (PROPHET) at the University of Michigan Biological Station in Pellston, Michigan. The measurements were conducted using on-line chromatography in conjunction with a nitrate-selective detection scheme. Measured concentrations of isoprene nitrates ranged from 0.5 parts per trillion (ppt), the detection limit of the method employed, to 35 ppt. In this paper we discuss the contribution of the isoprene nitrates to NOy, which was typically 0.5–1.5% of total odd nitrogen, but up to ∼4% for well-aged air. Concentrations of isoprene nitrates exhibited a strong diurnal variation consistent with their expected chemical and physical removal rates. In this work we also discuss the chemistry of the precursor peroxy radicals and the NOx dependence of isoprene nitrate formation.