1. Thermal decomposition ionization and reaction detection Pump electronics HV electronics Calibration Box

2. New PAN instrument: Chemical Ionization Mass Spectrometer based on Reaction of radicals with I - Fast Sensitive Selective Autonomous Slusher et al., JGR 2004

3. I - Chemistry I - reacts with N 2 O 5 and ClNO 3 –k = 1 x 10 -9 –product NO 3 - I- unreactive with PAN, HNO 3, HCl, SO 2, O 3, H 2 O, etc. Forms weak clusters with H 2 O, etc.

4. I - reactions with RO 2 I - + RO 2 → RO - + IO R = CF 3, CH 3 C(O), CH 3 CH 2 C(O), etc. i.e. RO - must be conjugated base of strong acid such as acetic acid used by Howard, Villalta, Froyd, deGouw, etc. to study kinetics of RO 2 + NO

5. CIMS Method Heated Inlet R-C(O)O 2 NO 2 → R-C(O)O 2 + NO 2 Detection I - + R-C(O)O 2 → RC(O)O - + IO Zero R-C(O)O 2 + NO → R-C(O)O + NO 2 or destroy PAN thermally before entering instrument

6. Then and Now Time resolution1.25-2.5 min0.25-2 sec Limit of detection2-3 pptv< 2 pptv/sec Sensitivity15-30 cps/pptv Background<200 cps # of PAN species48+ Instrument weight ~425 lbs~360 lbs (incl. Gases) (smaller Instr. coming) OperatorYes/NoNo!