Chandan Misra

Development and evaluation of a personal cascade impactor sampler (PCIS)

This paper presents development and evaluation of a personal sampler for particulate matter that allows separation of airborne particles by size. The Personal Cascade Impactor Sampler (PCIS) is a miniaturized cascade impactor, consisting of four impaction stages, followed by an after-filter. Particles are separated in the following aerodynamic particle diameter ranges: <0.25, 0.25–0.5, 0.5–1.0, 1.0–2.5 and 2.5–. The PCIS operates at a flow rate of using a very high efficiency, battery-operated light pump at a pressure drop of 11 in H2O (). PTFE (Teflon), quartz and aluminum substrates were chosen for characterization of the PCIS. Laboratory tests conducted with monodisperse polystyrene latex (PSL) particles as well as polydisperse ammonium sulfate and ammonium nitrate aerosols corroborated the cutpoints. Our experimental characterization identified Teflon filters as ideal impaction substrates because they result in high collection efficiency of particles above the cutpoint of each stage without the use of adhesive coatings, do not collect excessively particles below the cutpoint (a problem encountered with the use of quartz substrates) and because of their ability to be used for gravimetric analysis. Particle loading tests indicated that the PCIS stages could collect up to 3.16 and of fine and coarse PM, respectively, without any loss in the collection efficiency, which would have been a result of particle bounce.

A high flow rate, very low pressure drop impactor for inertial separation of ultrafine from accumulation mode particles

Abstract This paper presents the development and evaluation of a high-volume, multiple rectangular (slit) geometry jet impactor. Operating with a preselective inlet that removes particles larger than 2.5 μm in aerodynamic size, the impactor has been designed to separate ultrafine ( μm ) from the accumulation mode range ( 0.15 p μm ). Particles are accelerated by passing through 10 parallel slits nozzles, each 12.5 cm long by 0.0125 cm wide. The average jet velocity in each rectangular jet is approximately 5800 cm s −1 . Following acceleration, particles larger than approximately 0.15 μm impact on quartz fiber strips, each 12.5×0.5 cm 2 , while the aerosol fraction smaller than 0.15 μm penetrates through the outlet of the impactor. The impactor operates at a flow rate 550 l min −1 and at a very low pressure drop of 0.020 kPa . The performance of the multi-slit impactor was validated in laboratory and the field tests. Laboratory experiments conducted with monodisperse PSL particles as well as polydisperse ammonium nitrate, sulfate and indoor aerosols corroborated the 50% cutpoint of the impactor at 0.15 μm . Field test comparisons between the high-volume multi-slit impactor and the Microorifice Uniform Deposit Impactor (MOUDI) showed that the accumulation and ultrafine mode concentrations of particulate nitrate, sulfate, elemental and organic carbon are in very good agreement (within 10% or less). This impactor has been developed primarily as a separator of ultrafine from accumulation mode particles for use in human exposure studies to concentrated ambient ultrafine aerosols. High-volume collection of size-fractionated particulate matter accomplished by this impactor further enables investigators in the field of environmental health to conduct toxicological studies using ambient accumulation and ultrafine mode particles in vitro as well as by means of intratracheal instillation.

Development and evaluation of a continuous coarse (PM10-PM2.5) particle monitor.

ABSTRACT In this paper, we describe the development and laboratory and field evaluation of a continuous coarse (2.5-10 um) particle mass (PM) monitor that can provide reliable measurements of the coarse mass (CM) concentrations in time intervals as short as 5-10 min. The operating principle of the monitor is based on enriching CM concentrations by a factor of ~25 by means of a 2.5-um cut point round nozzle virtual impactor while maintaining fine mass (FM)—that is, the mass of PM2 5 at ambient concentrations. The aerosol mixture is subsequently drawn through a standard tapered element oscillating microbalance (TEOM), the response of which is dominated by the contributions of the CM, due to concentration enrichment. Findings from the field study ascertain that a TEOM coupled with a PM10 inlet followed by a 2.5-um cut point round nozzle virtual impactor can be used successfully for continuous CM concentration measurements. The average concentration-enriched CM concentrations measured by the TEOM were 26-27 times higher than those measured by the time-integrated PM10 samplers [the micro-orifice uniform deposit

Development and Evaluation of a Compact Facility for Exposing Humans to Concentrated Ambient Ultrafine Particles

This article presents the development and evaluation of a very compact facility for exposing humans to concentrated ambient ultrafine particles (da < 0.15 μm). The human ultrafine particle concentrator (UFPC) operates at an intake flow rate of 1200 liters per minute (LPM). The concentrator is preceded by an ultrafine impactor which separates the accumulation mode from ultrafine mode particles under a very low pressure drop (1.5 kPa), a feature that is essential in enabling human inhalation studies of ultrafine concentrated ambient particulates (CAP). A key feature of the UFPC is a new cooling system, consisting of a programmable refrigerated circulator, which produces the supersaturation that is necessary to grow ultrafine PM to supermicrometer sizes so that they can be concentrated by means of conventional virtual impaction. The new cooling system allows for entirely automated operation of the UFPC. The UFPC was characterized in field experiments, in which the concentration enrichment of ultrafine particles was determined based on their number and mass concentration as well as on chemical composition including elemental carbon (EC), inorganic ions (sulfate and nitrate), and polycyclic aromatic hydrocarbons (PAH). Tests were conducted at minor-to-total flow ratios varying from 2.5–5% (hence at minor flow rates between 30–60 LPM). Measurements with the scanning mobility particle sizer (SMPS) showed a near-ideal increase in number concentrations (corresponding to the ratio of total-to-minor flow rate) of ultrafine particles after enrichment. The concentration enrichment was uniform across the entire particle diameter range of 15–660 nm. Similar results were obtained for EC and PAH concentrations (measured by an Aethalometer). Time-integrated filter-based tests, conducted to characterize the system for ultrafine PM mass and inorganic ion concentrations showed that the average enrichment factor was very close to the ideal values, indicating near-perfect collection efficiency with minimal particle losses.

Development and Evaluation of a PM 10 Impactor-Inlet for a Continuous Coarse Particle Monitor

Conventional PM 10 inlets available operate at a flow rate of 16.7 l/min. The purpose of this study was to develop and test a PM 10 inlet designed to operate at 50 l/min to be used with a recently developed continuous coarse particle monitor (Misra et al.). Laboratory tests using polystyrene latex particles established the inlets 50% cutpoint at 9.5 w m. Further evaluation of PM 10 inlet was performed in a wind tunnel at wind speeds of 3, 8, and 24 km/h. Tests showed that the 50% efficiency cutpoint as well as the very sharp particle separation characteristics of the inlet were maintained at these wind speeds. Field evaluation of the PM 10 inlet was performed in Riverside and Rubidoux, CA. A 2.5 w m cutpoint round nozzle virtual impactor was attached downstream of the developed PM 10 inlet. The Dichotomous PM 10 Partisol Sampler, operating at a flow rate of 16.7 l/min was used as a reference sampler. The Dichotomous Partisol uses an FRM PM 10 inlet operating at 16.7 l/min to remove particles larger than 10 w m in aerodynamic diameter. Commercially available 4.7 cm Teflon filters were used in both the Partisol and the PM 10 inlet to collect particulate matter (PM). Results showed good agreement between coarse PM (2.5-10 w m) mass concentrations measured by means of the PM 10 inlet and Partisol. Chemical analyses showed excellent agreement between coarse PM concentrations of Al, K, Si, Ca, and Fe obtained by the two samplers. The agreement also persisted for nitrate and sulfate. Finally, the excellent agreement between coarse concentrations of the PM 10 inlet and Partisol persisted for wind speeds up to 19 km/h.