Journal: Science Advances
Article Title: Large contribution to secondary organic aerosol from isoprene cloud chemistry
doi: 10.1126/sciadv.abe2952
Figure Lengend Snippet: The experiment consists of six phases (all at 100% RH and 295 K). Phase I: Conditioning of the WFR flow tube in the dark to reach a steady state mixing ratio of 10 ppb v isoprene. Phase II: Initiation of the photooxidation by switching on the Xe-excimer lamps (in front of the WFR) and the ultraviolet B (UVB) lamps (around the WFR). Phase III: Injection of the water microfilm, denoted by the blue arrow. Phase IV: OH oxidation of isoprene only with the Xe-excimer lamps, bypassing the WFR. Phase V (same as phase III): Reaction mixture through WFR with both the Xe-excimer and UVB lamps on and the water microfilm present. Phase VI: UVB lights off. Phase VII: Both Xe-excimer and UVB lamps off. ( A ) Carbon mass balance of the gas phase derived from PTR-TOF-MS and acetate-CIMS. The red line presents the isoprene decay measured by the PTR-TOF-MS, indicating 42-ppb v C reacted isoprene carbon (corresponding to 8.4 ppb v of consumed isoprene). Gray stacked areas denote the increase of unique oxidation products measured by both the PTR-TOF-MS (dark gray) and the acetate-CIMS (light gray), with molecules encountered in both instruments only being counted via the PTR-TOF-MS. Ions with the same molecular formula from both instruments comprised 2.8 ± 0.7 ppb v C, indicating only 7 ± 2% of carbon overlap. ( B ) Measured (solid lines) and modeled (dashed lines; using the QEMRA model and calculated eff H values) evolution of selected nonsoluble (C 3 H 6 O) and soluble (C 5 H 10 O 5 ) oxidation products. ( C ) Representative uptake ratio after 5 hours of cloud processing as a function of the effective Henry’s law constant ( eff H ) color coded with the saturation vapor concentration ( C *).
Article Snippet: Around the WFR, nine ultraviolet B (UVB) lamps (Philips lamp TL 40W/12 RS) were used in certain experiments to start the photochemistry.
Techniques: Injection, Derivative Assay, Concentration Assay
