2012 Progress Report: A compact, low-cost, network accessible, optical particle counter for the real time measurement of submicron aerosol particle size distributionsEPA Grant Number: R835139
Title: A compact, low-cost, network accessible, optical particle counter for the real time measurement of submicron aerosol particle size distributions
Investigators: Bertram, Timothy H , Brady, James , Strokes, Dale
Current Investigators: Bertram, Timothy H
Institution: University of California - San Diego
EPA Project Officer: Chung, Serena
Project Period: February 1, 2012 through January 31, 2015
Project Period Covered by this Report: January 1, 2012 through April 24,2013
Project Amount: $250,000
RFA: Developing the Next Generation of Air Quality Measurement Technology (2011) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air
The objective of this project is the development of a miniature, wireless optical particle counter (OPC) capable of measuring and transmitting submicron aerosol particle number and size distributions to a remote server in real-time. The proposal aims to provide the framework for significant improvements in the spatial and temporal resolution of continuous aerosol particle measurements on the city scale, while dramatically improving the availability of these data in real time. To this end we proposed the development of a miniature OPC that incorporates a high power blue diode laser into the optical cavity of an existing commercial handheld OPC to measure submicron aerosol particle number and size distributions.
The year one research objective was to: “Develop and optimize the laboratory based optical particle counter and extensively characterize its response to a suite of laboratory and ambient aerosol particles.” To this end, we have built a laboratory based miniature OPC, that uses a 40 mW blue diode laser. The prototype is controlled by LabView, where scattered light from individual aerosol particles is detected by a Si PIN photodiode. The photodiode delivers a current pulse to a transimpedance amplifier to convert current to voltage. The laboratory based system is capable of measuring particles with diameters greater than 300 nm with pulse characteristics similar to those anticipated based on the hardware design (pulse width = 7 μs). In its current configuration, we have been operating the mini-OPC as a two channel instrument for sub- and supermicrometer aerosol detection. In parallel with these directions, we have designed a custom pulse height analyzer that will be used in conjunction with a 120 MHz microprocessor enabling the sensor to be both compact, autonomous, and wireless.
Year 2 and 3 efforts will focus on transferring data acquisition from the LabView based approach to a 120 MHz microprocessor that will serve as the imbedded intelligence for the device. This includes the use of a series of programmable gain amplifiers that feed the voltage pulses to a custom pulse height analyzer where the microcontroller then bins the sampled pulse heights into 10-256 size bins. Our year 2 efforts also will focus on rigorously defining the figures of merit for the device (sensitivity, minimum detectable size, size resolution, long-term precision), and response to particles of varying refractive indices.