Continuous Monitoring of Ambient Particulate Nitrate Concentration
The Series 8400N Ambient Particulate Nitrate Monitor provides measurements every 10 minutes of the atmospheric concentration of particulate nitrate in fine particulate matter (PM-2.5). It is based upon a patented, field-proven technology developed by Aerosol Dynamics, Inc.
The device is designed for long-term, automated collection and analysis of the particulate nitrate concentration. In its standard operational setting, the instrument generates a new particulate nitrate measurement in micrograms per cubic meter every ten minutes. It is a rack-mountable, automated monitor designed for continuous, unattended use in air quality monitoring stations, and contains the data communications capabilities required for use in air monitoring networks.
Its measurement includes ammonium nitrate and sodium nitrate, but does not include ammonium. Ammonium nitrate can be very difficult to quantify using conventional, filter-based techniques, since the species can volatile from filter materials at ambient air temperatures higher than 15 degrees C. The monitor is designed to avoid the difficulties associated with conventional, filter-based collection of particulate nitrate.
The Series 8400N monitor is being used by air quality monitoring agencies in the US and internationally to gain important information concerning secondary transformations that occur in the atmosphere. It has been used in many US and international supersites, and has most recently been included in a multi-site USEPA pilot study to investigate the performance of continuous PM speciation monitors.
Field measurements include campaigns conducted in Bakersfield (continuous and methods comparison),Fresno, Atlanta and the San Joaquin Valley.
Sample Collection
A stream of ambient air containing particulate matter enters a sample flow line that is surrounded by a sheath air flow that is used to maintain ambient temperature conditions inside the monitor. A sharp-cut cyclone removes coarse particles, and the sample stream is then conditioned as it passes through a charcoal honeycomb denuder and is humidified. The fine particles contained in the sample flow impact and are collected on strip of metal located in the integrated collection and vaporization cell.
During sample analysis, the monitor purges the analysis cell with nitrogen, and sends a high current through the impactor/flasher strip for approximately 0.05 seconds to heat the collected particulate matter to approximately 350 degrees C. The vaporization decomposition process converts the particulate nitrate contained in the collected sample to NOx, which is quantified by a specially-tuned pulse monitor.
The instrument automatically computes the concentration final result as the particulate nitrate concentration in micrograms per cubic meter, storing the information internally and transmitting it to external devices through analog and serial interfaces.
The analytical technique used in the Series 8400 monitor has undergone thorough laboratory testing with aqueous standards as well as monodispersed nitrate aerosols. In the field, the operation of the monitor with bottles of NO span gas and N2 provides the basis for self diagnostics of the pulse monitor. The instrument also contains diagnostic routines for detecting potential leaks and flow conditions. Operating and diagnostic statistics may be viewed on the instrument display through the menu-driven operating software or downloaded by bi-directional RS232.
0 Items 
