1. Chebatoris, A.W., Harvey, J.W., Hess, B.T., Krepps, J.P., O’Brien, K.A., Short, D.B., and Spaulding, R.E. Abstract Nitrogen dioxide is a criteria air pollutant regulated by the Federal Government. The gas was measured locally using the passive diffusion technique, values obtained were then compared to other monitoring sites in the same area. Introduction Nitrogen dioxide (NO 2 ) is one of six pollutants routinely monitored by the Environmental Protection Agency (EPA) under the National Ambient Air Quality Standards (NAAQS). The main sources of NO 2 are vehicular traffic and the production of energy from fossil fuels. The main environmental impacts of NO 2 is as a precursor of acid rain, tropospheric ozone, and fine particulate pollution. NO 2 is routinely monitored at fixed sites using a chemiluminescent active (instantaneous) sampling technique. An alternative (time- weighted) technique known as Passive Diffusion Tubes (PDT) is available that allows for greater flexibility in sample location and is more cost effective for monitoring a larger number of remote sites [1]. Field Sampling PDTs were placed in various locations across Allegheny county (fig. 1) in order to determine atmospheric NO 2 levels. Method Nitrogen dioxide concentrations were determined using a passive wet chemical technique developed over the last 35 years and reviewed by Varshney and Singh (2003). Briefly, atmospheric NO 2 diffuses into the tube where it is absorbed onto a stainless steel mesh coated with an absorbent chemical (triethanolamine). Fick’s law of diffusion is then used to quantify the concentration of NO 2 in the air. Discussion The average NO 2 concentration recorded for March over the last four years and around the city of Pittsburgh was 15 ppb, this concentration is well below the EPA standard of 53 ppb. The concentration recorded by PDTs is slightly lower than the average of 18 ppb recorded at a continuous chemiluminescent monitor in the city (EPA1) between 2005- 2009 (fig. 2). Pittsburgh NO 2 levels for the past decade are compared with 3 other major cities in figure 3. References [1] Varshney, C.K. and Singh, A.P. (2003) Passive Samplers for NOx Monitoring: A Critical Review. Environmentalist, Vol. 23, No. 2, pp. 127- 136. [2] EPA Air Data: http://www.epa.gov/air/data/index.html, 03/11. Results T able 1 shows the average of 5 diffusion tube measurements for the month of February/March from 2008-2011. Figure 2 shows a comparison between PDT values and average monthly EPA NO 2 monitor (chemiluminescent) values. Table 1: Nitrogen dioxide values measured in Allegheny county during March 2011. Figure 2: PDT measurements vs. instantaneous monitors. Figure 3: Nitrogen dioxide trends in major US cities. Figure 1: Location of Nitrogen dioxide sampling sites in Allegheny county (March 2011). Latitude/LongitudeNO 2 in Air (ppb) 40 ° 21'19.25"N, 80 ° 08'28.75"W 12 40 ° 22'09.34"N, 79 ° 49'43.56"W 14 40 32'17.23"N, 80 05'02.38"W8 40 24'28.84"N, 80 06'35.22"W14 40°17'09.07"N, 79°43'59.37"W11 40°26'14" N, 80°1'10" W15 40°31' 28"N, 80°13' 34"W7