S9 Laboratory Generation of HO Radicals and Their Effects on Vehicle Emissions in a TiO2 Coated Setting

Sunday, 6 January 2013
Exhibit Hall 3 (Austin Convention Center)
Kallie B. Doeden, St. Olaf College, Northfield, MN; and C. Toro and B. T. Jobson

This study focuses on the methodology of generating and measuring HONO to study its potential formation from self-cleaning surfaces such as TiO2.   A HONO-generating system was built and optimized by reacting a humid nitrogen stream containing gaseous HCl with solid sodium nitrate and passing the flow through a set of denuders to remove HNO3. The HONO produced was quantified by measuring its presence as NOx using a TECO Model 42 chemiluminescence NO-NO2-NOx analyzer containing a molybdenum catalyst. NO and NO2 are commonly classified as NOx. However, the TECO measures NOx as NO, NO2, HONO and HNO3. The optimum arrangement produced 84.7 ppb of NOx of which 16.2 ppbv was HONO and 68.5 ppbv was HNO3 in a 685 mL/min flow diluted to 5 L/min.   In a second set of experiments, a 150-L Teflon chamber was filled with HONO and also HONO and toluene and exposed to blacklight illumination. HONO photolyzed to produce the HO radical that oxidizes toluene. A proton-transfer-reactor mass spectrometer was used to measure the decay of toluene and generation of oxidation products. HONO generation from TiO2 coated concrete was also measured.
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