Dieterich, M.F., Gieseler, M.E., Short, D.B., and Signorelli, R.T. Abstract Nitrogen dioxide is a criteria air pollutant regulated by the Federal Government.This research compared two passive sampling devices for measuring nitrogen dioxide in the atmosphere. The data revealed comparable values of nitrogen dioxide concentrations for both devices. Introduction Nitrogen dioxide (NO 2 ) is one of a group of highly reactive gasses known as “nitrogen oxides“(NO x ). Major sources of NO 2 include vehicular traffic and the production of energy from combusting fossil fuels. The US Environmental Protection Agency (EPA) standard for atmospheric NO 2 is 53 parts per billion (ppb), averaged annually, to protect the health and public welfare [1]. This federally mandated standard is monitored continuously in Allegheny County by the Allegheny County Health Department (ACHD) and the Envionmental Protection Agency (EPA) using a chemiluminescent (instantaneous) monitoring technique. This project utilized two alternative methods of sampling NO 2 known as the Palmes Diffusion Tubes (PDTs) technique and the Rapid Air Monitors (RAMs) technique. These methods are well established and are wet chemical time weighted techniques that allow for greater flexibility in sampling location, and are more cost effective when monitoring larger areas with multiple sites [2]. A custom-made PDT was created for this experiment, using the standards from AEA Group [3]. The RAM device is manufactured by Gradko International. RAMs were designed to lessen the length of time a PDT is required to be deployed in the field, which is around 4 weeks for an urban site. Field Sampling On the lower left is a disassembled RAM. On the lower right is a disassembled PDT. These two sampling devices were placed in various locations across Allegheny County, PA in order to determine atmospheric NO 2 levels. Method Atmospheric NO 2 concentrations were determined using a technique of passive wet chemical developed over the last 35 years for the Palmes diffusion tubes (PDT) and reviewed by Varshney and Singh (2003). Importantly, atmospheric NO 2 diffuses into the PDT tube where it is absorbed onto a stainless steel mesh coated with an absorbent chemical (triehanolamine). To measure the quantity of NO 2 Fick’s law of diffusion was applied. The rapid air monitors (RAMs) were analyzed according to the manufacturers (Gradko Company) specifications. This new device employs the same colorimetric determination as the PDTs, however instead of using Fick’s law a temperature dependent sample uptake equation is used. Discussion The NO 2 concentrations, recorded at site one in Table 1, were 20 ppb measured with a RAM and 17 ± 6 ppb measured with PDT’s. The NO 2 concentrations recorded at site two were 16 ppb measured with a PDT and 14 ppb measured with a RAM. There were no standard deviations recorded from site 2. The 4 week RAM and PDT measurements from both site 1 and 2 were recorded concurrently which indicates both devices measured NO 2 concentrations with similar efficiencies. Site three’s NO 2 measurement for March was 14 ± 1 ppb. Monthly NO 2 concentrations at site 3, recorded over a four year period between February and March of each year, were between 15 and 20 ppb. The 2 week value of 5 ppb recorded at site 3 compares favorably with this concentration range. Figure one shows a weekly comparison of RAM values to demonstrate that it is functional over a weekly time frame. We plan to further assess the accuracy of the RAM device against PDTs by increasing our sample size. Once a higher precision is achieved we plan to compare a weekly RAM measurement with average weekly chemiluminescent measurements taken in this area. References [1] EPA Air Data: 03/11. [2] Varshney, C.K. and Singh, A.P. (2003) Passive Samplers for NOx Monitoring: A Critical Review. Environmentalist, Vol. 23, No. 2, pp [3] AEA Diffusion Tube Methods: practical-Guidance.pdf, 4/12. Results Table 1 compares the NO 2 concentration reported for RAMs and PDTs tested for a duration of two weeks in the month of April of Figure 2 shows the average concentration of NO 2 (in ppb) at each site comparing the duration of time that the RAM devices were tested. Table 1: RAM and PDT recorded NO 2 concentrations. Data that include a standard deviation (SD) value indicate the average of two measurements and data without a SD is one measurement. RAMPDT 1 Wk2 Wk4 Wk Location NO 2 (ppb) SD NO 2 (ppb) SD NO 2 (ppb) SD NO 2 (ppb) SD Site Site Site Figure 1: Atmospheric NO 2 field measurement devices (RAM and PDT). Figure 2: Comparison of atmospheric NO 2 concentrations measured with RAM devices for a duration of 1-4 weeks.