3506B24 Final Report
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- HNO3cal 5 0:45 0:05 NO2cal5
- NO2cal1 90 6:34 0:04
- NPNcal1 100 1:20 0:07
- NPNcal2 75 1:27 0:03
- NPNcal3 50 1:30 0:03
- NPNcal4 25 1:33 0:03
- NPNcal5 10 1:36 0:03
- NOcal1 90 2:20 0:07
- NOcal2 75 2:27 0:03
- NOcal3 50 2:30 0:03
- NOcal4 25 2:33 0:03
- NOcal5 10 2:36 0:03
- O3cal1 360 4:20 0:04
- O3cal2 270 4:24 0:03
- O3cal3 180 4:27 0:03
- O3cal4 120 4:30 0:03
- O3cal5 60 4:33 0:03
- O3zero 0 4:36 0:03
- COcal1+zero >0 5:20 0:03
- COcal1 6000 5:23 0:04
- COcal2 4500 5:27 0:03
- COcal3 3000 5:30 0:03
- COcal4 2000 5:33 0:03
- COcal5 1000 5:36 0:03
- Table 8
F  igure 16: Flow diagram of the modified TEI 146C calibrator with added selector valve (SV) for sending NO, NO2, and NPN calibration gas to the inlet box on the tower or calibrating the O3 or CO analyzers.
Figure 17: Flow schematic of the TEI 42CY NO/NOy inlet box mounted at ~6 mag receiving NO, NO2, NPN, and HNO3 calibration gases from below. The calibration valve (CV) allows maintain a well-equilibrated HNO3 calibration gas delivery, leaving only a very small tube section between the CV’s NC-port and the tee at the sample line to be equilibrated upon CV activation. Automated calibrations were performed daily via a programmed set of NO, NO2, n-propyl nitrate (NPN), and HNO3 standard calibrations in zero air. Zero air, i.e. contaminant-free air was provided by a TEI 111 Zero Air Generator supplied with ambient air from a generic 1/8 hp compressor at ~40 psi. NIST-certified NO and NPN standard calibration gases were used at mixing ratios of 5.95 ppmv and 6.20 ppmv in N2, respectively. NO2 was generated within the 146C via gas phase titration with O3 generated from UV photo-dissociation of O2. HNO3 was provided from a permeation tube (Kintek) with certified rate of 30 ng/min at 45 °C operated at constant flow and temperature inside the permeation oven of the 146C calibrator, yielding nominal 5 ppbv. As illustrated in the flow schematic (Figs. 16 and 17), the HNO3 calibration gas was sent up to the inlet in a PFA line separate from the other calibration gases, in order to keep all surfaces that come in contact with the HNO3, incl. the 2-way 3-port Teflon valve at the inlet, well equilibrated, minimizing the surface area when the valve is switched for calibration mode, and therefore minimizing the response time of the system. Table 7: Sequence of automated zeros and multipoint calibrations subjected to the continuous NO, NOy, O3 and CO measurements at OLC and other FAQS monitoring sites.
According to the schedule listed in Table 7, the analyzer was subject to 5-point calibrations for NO and NPN with mixing ratios of 90 (100 for NPN), 75, 50, 25, and 10 ppbv once every 23 h. The nominal mixing ratios were generated by dynamic dilution of the calibration gas from the certified tank and zero air using calibrated Mass Flow Controllers (MFC) inside the 146C. 
Figure 18: Time series of the continuous gas analyzers individual signal responses to the programmed sequence of multi-point calibrations and zero checks (see Table 7). The 1 min data were typically reduced on a monthly basis, and the analyzer’s responses to the hourly zero air applications and daily (every 23 h) 5-point calibrations plotted against the nominal values and linearly regressed. The slope of these regressions representing the analyzer’s sensitivity for NO and NOy (using NPN) averaged 20 and 21 ppbv/Vdc with a typical 1-σ uncertainty of ± 0.01 (0.05%) and ± 0.02 (0.1%), respectively. The intercepts varied slightly from month to month, averaging for both at 0, but at a larger variability for NOy, i.e. 0 ±0.5 ppbv for NO and ±1 ppbv for NOy. On a monthly basis, however, the detection limits expressed as 1-σ uncertainties of the intercepts ranged between 0.01 ppbv for NO and 0.02 ppbv for NOy, which is similar to the 1-σ variability of the monthly zeros. While the NPN calibrations were used to convert the NOy analog signal, with each calibration cycle, the MoO converter was checked for its efficiency to convert also NO2 and HNO3, which was near 100 % for NO2 but significantly less for the generally harder to convert HNO3 at ~80 %, adding uncertainty to the NOy measurement. The data quality indicators (DQIs) assessed above are summarized in Table 8, with τ being the instrument’s response time in reaching 90 % of its end value signal. Table 8: Average trace gas data quality indicators (DQI) with the instrument’s response time τ, and lower detection limit (DL) for 1 and 30 min integration.
5.1.5 Semi-Continuous PM2.5 Mass (TEOM) Fine PM mass was measured continuously by the patented Tapered Element Oscillating Micro-balance (TEOM) technology developed by Rupprecht & Patashnick Co., Inc., Albany, NY. The Series 1400a Monitor is a true “gravimetric” instrument that draws ambient air through a filter at a constant flow rate, continuously weighing the filter and calculating near real-time (5 min) mass concentrations. In addition, the instrument computes the total mass accumulation on the collection filter, as well as 30 min, 1, 8 and 24 h averages of the mass concentration. The TEOM operated at OLC was identical to the ones run at the other 3 FAQS monitoring sites. It employed the Sample Equilibration System (SES) with relative humidity control using Nafion® dryer technology to condition the main and bypass sample streams to low humidity and temperature levels. The SES permits fine PM mass measurements to be performed in a manner that minimizes the possibility of PM concentrations being overestimated due to the affinity that some types of particles have for moisture (hygroscopicity). It allows the mass collected on the filter to equilibrate more rapidly than when in the presence of high humidity levels. Nafion is a Teflon material with occasional side chains of another fluorocarbon called a sulfonic acid group. It is the sulfonic acid group’s high affinity to water that allows Nafion dryers to function. The devices are similar to shell-in-tube heat exchangers that employ an outside shell and strands of Nafion tubing down the center. Although water passage through the Nafion is described as “permeation,” Nafion dryers do not operate on the same principle as permeation dryers. Nafion is not a micro-porous material that separates compounds on the basis of their molecular size. For example, Nafion dryers can remove water from a hydrogen stream even though the hydrogen molecule is much smaller than the water molecule. Pressure is not required to drive the drying process. The driving force of the reaction inside the Nafion dryer is the difference in water vapor content between the sample and purge gas streams. When water strikes an exposed sulfonic acid group on the surface of the Nafion dryer tubing, the water is initially bound. Additional sulfonic acid groups deeper in the wall of the tubing have less water attached to them, and consequently a higher affinity to water. Water molecules absorbed onto the surface of the tubing are therefore quickly passed on to the underlying sulfonic acid groups until the water reaches the opposite side. This process continues until the water pressure vapor gradient across the tubing wall is eliminated. If a dry purge gas flows over the exterior surface of the Nafion tubing, water vapor will be continuously extracted from the gas stream inside the tubing until the sample humidity matches that of the purge gas. The relative humidity levels typically achieved with this set-up were 15 ±3 %. When the instrument samples, the ambient sample stream first passes through the PM10 inlet followed by the PM2.5 Sharp-Cut Cyclone (SCC) in line. At its design flow rate of 16.7 lpm, this inlet combination has a sharper cut-point efficiency than conventional single-stage inlets [Kenny and Gussman 1997], allowing particles smaller than 2.5 μm diameter to pass through. The SCC inlet combination was mounted to the Al tower at ~6 mag, and ~7 m long carbon conductive tubing with ID of 0.6 cm was used to draw the sample air down into the shelter. At a residence time τ = 0.7 s and Re= 3700, transition between laminar and turbulent flow, the PM2.5 transmittance is >99%. At the top of the TEOM sensor unit inside the shelter, the 16.7 lpm flow was iso-kinetically split into a 3 lpm sample stream that was sent through the Nafion dryer to the instrument’s mass transducer, and a 13.7 lpm exhaust stream. Figure 19 depicts a flow schematic of the setup used here for the TEOM PM2.5 mass measurements. 
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