ICARUS Chamber Experiment: 2014 FIXCIT Study_20140107_ISOPRENE/Methyl nitrite_Hydroxyl radical_No Seed_Isoprene + OH "slow chemistry" (isomerization), dry, 40C, no seeds

Goals: To make parts-per-billion-by-volume levels of HPALDs and associated compounds and observe their response in the suite of instrumentation. To photooxidize HPALDs and associated compounds and observe product species. Determination if HPALD (or associated compounds) contributes toward interference on OH instrument. Summary: Overall, the experiment went well. Initial NO levels in the high NOx bag were ~500 pptv which we believe was a result of connecting the GTHOS instrument to the bag shortly before starting the experiment. The HPALD compounds were formed overnight by photolyzing CH3ONO in the presence of isoprene under low levels of UV light, at 40C. By 10AM HPALD levels were ~1.3 ppbv as observed by CF3O- CIMS, and isoprene had decayed by a factor of 2. After the initial rapid NO decrease to stationary level (~70 pptv), NO remained stable over the low light portion of the experiment. After instrumentation began sampling the reaction products, the low level UV lights were turned off, and then temperature was ramped down to 25C, and then back up to 40C over the period of an hour. Next, 20% of chamber UV lights were turned on for 45 minutes, and then 100% UV lights were illuminated for approximately 1.5 hours. When the high level of UV lights were turned on, the AMS detected particle nucleation, and NO3- CIMS observed increases in several ion signals. Organization: 2014 FIXCIT Study Lab Affiliation: California Institute of Technology Chamber: Seinfeld chambers Experiment Category: Gas phase chemical reaction Oxidant: Hydroxyl radical Reactants: ISOPRENE, Methyl nitrite Reaction Type: Photooxidation Relative Humidity: 5 Temperature: 40 Pressure: 750 Torr