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Biomedical subjects

Peter H McMurry

Publications and source records attributed to Peter H McMurry.

6 recordsLinked to original sources
PubMed2006

Chemical and physical properties of ultrafine diesel exhaust particles sampled downstream of a catalytic trap.

The chemical and physical properties of exhaust particles produced by a Caterpillar 3176 C-12 heavy duty diesel engine equipped with a catalytic trap (CRT) are reported. The engine was operated at 600 Nm and 1500 rpm, using fuels containing 15 and 49 ppm sulfur. A two-stage dilution tunnel designed to simulate the reactions that occur when hot combustion products mix with cooler atmospheric air was used. Particle size distributions were measured using a scanning mobility particle sizer (SMPS) and nano-scanning mobility particle sizer (nano SMPS); a nanomicro-orifice uniform deposit impactor (nano MOUDI) collected size-resolved samples for gravimetric and chemical analysis. A nanometer tandem differential mobility analyzer (nano TDMA) was used to measure the volatility and hygroscopicity of 4-15 nm particles. These measurements confirm that the particles consisted primarily of sulfates.

Air Pollutants↗
PubMed2003

Size-dependent mixing characteristics of volatile and nonvolatile components in diesel exhaust aerosols.

Mixing characteristics of particles of different volatilities from a diesel engine were studied with two tandem differential mobility analyzers (TDMAs) and an aerosol particle mass analyzer (APM). In both TDMA systems, a heater was located in the aerosol path between the first and second DMAs. Diesel exhaust particles that were size-selected in the first DMA were passed through the heater, and the change in particle size due to loss of volatile components was determined by the second DMA. On the basis of the volatility measurements, the particles could be separated into two overlapping modes that varied in peak diameter and magnitude depending on the engine operating conditions. Particles in the smaller size mode were almost completely volatile, while those in the larger size mode contained a nonvolatile core. The TDMA data inversion technique used here allowed accurate determination of the mixing ratios of the two types of particles. These data were in turn used to validate a simple fitting method that uses two log-normal curves to obtain the mixing ratios. In some experiments, the APM was used downstream of a TDMA to directly measure the particle mass loss due to evaporation. The loss determined bythe TDMA-APM system was significantly greater than that calculated from mobility size changes measured solely with the TDMA. The TDMA-APM results were used to calculate the size-dependent mass concentrations of volatile and nonvolatile components for particles in the size range from 70 to 200 nm.

Aerosols↗
PubMed2003

Relationship between particle mass and mobility for diesel exhaust particles.

We used the aerosol particle mass analyzer (APM) to measure the mass of mobility-classified diesel exhaust particles. This information enabled us to determine the effective density and fractal dimension of diesel particles as a function of engine load. We found that the effective density decreases as particle size increases. TEM images showed that this occurs because particles become more highly agglomerated as size increases. Effective density and fractal dimension increased somewhat as engine load decreased. TEM images suggest that this occurs because these particles contain more condensed fuel and/or lubricating oil. Also, we observed higher effective densities when high-sulfur EPA fuel (approximately 360 ppm S) was used than for Fischer-Tropsch fuel (approximately 0 ppm S). In addition, the effective density provides the relationship between mobility and aerodynamic equivalent diameters. The relationship between these diameters enables us to intercompare, in terms of a common measure of size, mass distributions measured with the scanning mobility particle sizer (SMPS) and a MOUDI impactor without making any assumptions about particle shape or density. We show that mass distributions of diesel particles measured with the SMPS-APM are in good agreement with distributions measured with a MOUDI and a nano-MOUDI for particles larger than approximately 60 nm. However, significantly more mass and greater variation were observed by the nano-MOUDI for particles smaller than 40 nm than by the SMPS-APM.

Air Movements↗
PubMed2002

Size distributions of 3-100-nm urban Atlanta aerosols: measurement and observations.

Size distributions of urban Atlanta, Georgia, aerosols (0.003-2 microm) were measured from August 1, 1998 through August 30, 2000 as part of the Aerosol Research Inhalation Epidemiology Study (ARIES). Size distributions were measured five times per hour, and approximately 50,000 size distributions were measured during the 25-month study. This paper focuses on salient features of the sub-100-nm data. We examine concentrations of particles in six equally spaced logarithmic intervals and show that particles of different sizes have distinctly different behaviors. For particles between 10 and 100 nm, average concentrations tended to be highest during winter, during rush hour, and on week days. Concentrations of particles in the 3-10-nm range were elevated in the summer due to photochemically driven nucleation, and also during winter. We hypothesize that the elevated wintertime concentrations of these particles were associated with nucleation that occurs as vehicular emissions mix with the cool ambient air. In any given size range, distributions of concentrations tend to be lognormal, but significant deviations from lognormality were occasionally observed. For particles in the 3.2-5.6-nm diameter range, deviations were apparent in the summer when very high concentrations (up to 10(6) cm(-3)) were produced by photochemically driven nucleation. During 2 months of the study, deviations from lognormality for particles in the 32-56-nm diameter range occurred when anomalously high concentrations of 40-nm particles were observed.

Aerosols↗