Air pollutant emission from unconfined sources is an increasingly important environmental issue. The U.S. Environmental Protection Agency (EPA) has developed a ground-based optical remote-sensing method that enables direct measurement of fugitive emission flux from large area sources. Open-path Fourier transform infrared spectroscopy (OP-FTIR) has been the primary technique for acquisition of pollutant concentration data used in this emission measurement method. For a number of environmentally important compounds, such as ammonia and methane, open-path tunable diode laser absorption spectroscopy (OP-TDLAS) is shown to be a viable alternative to Fourier transform spectroscopy for pollutant concentration measurements. Near-IR diode laser spectroscopy systems offer significant operational and cost advantages over Fourier transform instruments enabling more efficient implementation of the measurement strategy. This article reviews the EPA's fugitive emission measurement method and describes its multipath tunable diode laser instrument. Validation testing of the system is discussed. OP-TDLAS versus OP-FTIR correlation testing results for ammonia (R 2 ϭ 0.980) and methane (R 2 ϭ 0.991) are reported. Two example applications of tunable diode laser-based fugitive emission measurements are presented.

A differential optical absorption spectrometer for measurements of low-level sulfur dioxide (SO2) emissions from vehicles in real time was developed and employed. With a time resolution of 3 s and an optical path length of 19.6 m, a minimum detection limit of 75 ppbv SO2 (three times the standard deviation) was achieved. The wavelength region covered, UVB, was chosen to include the major SO2 absorption feature at 300 nm, while avoiding wavelength regions in which other components of vehicle exhaust are known to absorb. However, formaldehyde was found to be present in vehicle exhaust in high enough concentrations to be a major interferent. The analysis software was modified to account for the formaldehyde interferent using a two-dimensional fitting routine. The application of the instrument to real vehicle exhaust demonstrated that it was capable of measuring the contribution to SO2 emissions from lubricant oil sulfur over the range of current and future oil sulfur levels.

Static SIMS is now widely accepted as a surface mass spectrometry technique providing surface analysis with a very high degree of chemical precision. Many early catalyst-based studies of adsorption and surface reaction helped to establish this capability. These studies demonstrated the sensitivity of static SIMS to surface chemical structure. However, although the capability of static SIMS to characterize surface chemistry with high precision has great potential in this area, it has not been as widely applied in catalytic studies as might have been expected. By reviewing three very different studies from our own laboratory, this paper illustrates the capability of static SIMS to study the detail of surface reactions at single-crystal metal surfaces, to monitor and investigate the surface chemistry of an auto-exhaust catalyst and to investigate ice-catalysed reactions responsible for ozone depletion in polar stratospheric clouds.

A numerical study is performed to examine the effect of introducing a swirling desolvation gas flow on the flow transport characteristics in an electrospray and an atmospheric pressure chemical ionization (APCI) system. An ion source having three coaxial tubes is considered: (1) an inner capillary tube to inject the liquid sample, (2) a center coaxial tube to provide a room temperature gas flow to nebulize the liquid, referred to as the nebulizing gas flow, and (3) an outer coaxial tube having a converging exit to supply a high temperature gas for droplet desolvation, referred to as the desolvation gas flow. The results show that a swirling desolvation gas flow reduces the dispersion of the nebulizing gas and suppresses turbulent diffusion. The effect of swirling desolvation flow on the trajectory of a range of droplet sizes emitted from a source is also considered.

Titration of pesticides onto sorption sites can determine sorption capacities on soils. Previous studies have tracked the sorption capacities and detailed kinetics of the uptake of atrazine and its decomposition byproduct hydroxyatrazine on different soils, including measurements made using LC-MS/MS. These studies have now been extended to explore sorption-desorption equilibria for a mixture of pesticides from soil using LC-MS/MS. Desorption of sorbed pesticide residues has environmental regulatory implications for pesticide levels in runoff, or for longer term sequestration, partitioning, and transport. The uptake of pesticides by the soil at equilibrium was measured for a number of different concentrations, and sorption capacities were estimated. Pesticide-soil interaction studies were conducted by exposing standard stock solutions of pesticide mixtures to a characterized Nova Scotia soil. The mixture contained atrazine and dicamba. Initial aqueous mixture concentrations ranging from 5 × 10 −9 to 10 −5 M or greater were exposed to 25 mg aliquots of soil and allowed to reach equilibrium. The total uptake of each pesticide was measured indirectly, by measuring the concentration remaining in solution using an IONICS 3Q 120 triple quadrupole mass spectrometer. These sorption capacities have been supplemented by studies examining equilibrium recovery rates from soil aliquots with different initial uptakes. This gives insight into the fraction of easily recoverable (reversibly sorbed) pesticides on the soil. Proper quantification of equilibrium constants and kinetic rate coefficients using high performance LC-MS/MS facilitates the construction of accurate, predictive models. Predictive kinetic models can successfully mimic the experimental results for solution concentration, labile sorption, and intra-particle diffusion, and could be used to guide regulatory practices.