Raymond M. Hoff

Measurement of the particle-size distributions of semivolatile organic contaminants in the atmosphere.

A method using a Berner five-stage, low-pressure cascade impactor was developed to measure the particle-size distributions of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere. Possible sampling artifacts that may occur when sampling semivolatile organic chemicals with this low-pressure particle impactor(e.g., absorption of vapors onto sampler surfaces or volatilization of analytes from collected particles under reduced pressures within the impactor) were quantified for a variety of PAHs in the laboratory. At 20°C, these artifacts were insignificant for the collection of PAHs with vapor pressures less than 10 -8 atm. Several samples collected at a rural site (Egbert, Ontario) and an urban location (Chicago, IL) demonstrate the utility of the Berner impactor to collect PAHs under a variety of field conditions. At both the rural and urban locations, sufficient quantities of particles were collected in the five aerodynamic equivalent diameter size ranges (0.04-0.14, 0.14-0.49, 0.49-1.7, 1.7-6, and 6-21 μm) during 12 h to provide detectable levels of PAHs. PAHs were most often associated with particles less than 1.7 μm in both the rural and urban areas based on a limited number of observations (N= 5).

Measurement of polycyclic aromatic hydrocarbons in the air along the niagara river

Two week-long studies in 1982-1983 have measure ambient concentrations of polycyclic aromatic hydrocarbons (PAH) and phthalate esters in air in both the particulate and gas phase along the US-Canadian border and the Niagara River. Concentrations of the PAH species monitored varied from 3 pg m/sup -3/ to 40 ng m/sup -3/. PAHs with three rings or less were found in significant proportions in the gas phase while larger molecules are almost solely in the particulate phase. Particulate components of the PAH loadings appear to originate locally with Buffalo, NY, Niagara Falls, NY, and Niagara Falls, Ontario, as probably sources. Gas-phase PAH components have a more regional character indicating regional or long-range transport. Levels of benzo(a)pyrene are consistent with previous particulate measurements made along the river since 1981.

Dispersive correlation spectroscopy: a study of mask optimization procedures.

A procedure has been established to obtain the design parameters of the masks used in dispersive correlation spectrometers. The SNR equations are used to derive the mask equations. These are later solved for some simplified band models, and the obtained parameters are used as the initial values in an iterative program which determines the final design parameters. The calculations can be performed for various backgrounds and instrumental line profiles in order to achieve the best compromise for the detection of pollutants, and other trace gases, in the atmosphere.

ORACLE (Ozone Research with Advanced Cooperative Lidar Experiment): joint NASA-CSA development of a space-based ozone dial

This paper is presented to give a general description of the ORACLE project and of the technology development results obtained to date. ORACLE is a feasibility study of a fully automated differential absorption lidar for global measurements of tropospheric and stratospheric ozone and aerosols with high vertical and horizontal resolution. The proposed program includes both novel technology demonstrations and obtaining scientific data from spacecraft. These data are needed to address key issues in atmospheric research including the depletion of stratospheric ozone, global warming, atmospheric transport and dynamics, tropospheric ozone budgets, atmospheric chemistry, and the atmospheric impact of hazards. Only a space-based lidar system can provide the required spatial resolution for ozone and aerosols in both the stratosphere and the troposphere on a global scale at all required altitudes. To deliver these data, the most novel technologies such as all-solid-state lasers, photon-counting detectors and ultra-lightweight deployable telescopes must be employed in the mission payload.