3506B24 Final Report
Nitrogen Oxide and Sum of TotalReactive Nitrogen Oxides
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5.1.4 Nitrogen Oxide and Sum of TotalReactive Nitrogen OxidesA TEI 42C NO/NOy analyzer (Thermo Environmental Instruments, Inc., Franklin, MA) with external MoO converter was deployed for the measurement of NO and total reactive nitrogen oxides (NOy) that include NO, NO2, NO3, N2O5, HONO, HNO3, aerosol nitrate, PAN and other organic nitrates. These measurements were based on the principal method of metal-surface induced reduction of the more highly oxidized species to NO [Fahey et al. 1985; 1986; Fehsenfeld et al. 1987; Atlas et al. 1992; Parrish et al. 1993; etc.], and its subsequent chemiluminescence detection (CLD) with excess ozone [Ridley and Howlett 1974; Kley and McFarland 1980; Bollinger 1982; Fehsenfeld et al. 1990]. The metal surface here was provided by multiple layers of ~3 cm diameter MoO meshed disks stagged into a 10 cm long SS cartridge (TEI part # 9269), temperature controlled at 300 ±2 oC, and housed inside an inlet box mounted to the Al tower at ~7 m agl, see photograph in Figure 15. The plumbing was modified to allow for frequent instrument zero checks, NO calibrations and MoO converter efficiency checks for NO2, NPN, and HNO3 according to the flow schematic in Figure 16 and the automated sampling scheme listed in Table 7 with individual analyzers’ Vdc signal responses depicted in Figure 17. The sample air was drawn continuously through a 15 cm long 1.3 cm OD PFA tube, which extended to the outside bottom of the box and was coupled to a PFA-coated SS cross, where the flow was diverted to the MoO converter for the NOy and a bypass PFA tube of same length for the NO measurement, at ~1 slm respectively. Each flow was filtered by a Teflon membrane filter (Gelman-Teflo) with 2 m pore-size, and directed via 6 mm PFA tubing run inside a protective umbillical down the tower to the NO and NOy ports of the analyzer inside the shelter on the ground. The sample residence time inside the PFA tubing between the inlet box and the CLD unit inside the shelter was ~5 s. The chemiluminescence occurred in a gold-plated reaction vessel in front of a single red photon sensitive PMT at ~250 Torr. The analyzer internally switched every 10 s between NO measure, NO zero, NOy zero and NOy measure modes, updating the analog NO and NOy signals every 20 s, which were recorded as 1 min averages.  
Figure 15: Tower overview with met sensors (wind speed and direction top left, PAR top right, ambient T/RH probe below right), TEOM cyclone inlet (center left) and NO/NOy inlet box (left), and plumbing details of NO/NOy inlet box (right). 
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