1. U. Dusek 1, R. Holzinger 1, T. Röckmann 1 Institute for Marine and Atmospheric research Utrecht (IMAU), Utrecht University, The Netherlands Combined measurements of organic aerosol isotopic and chemical composition – A day/night test case

2. ORGANIC AEROSOL CHARACTERIZATION Combination of 3 relatively new techniques: 14 C: fossil (no 14 C) vs. non-fossil sources 13 C: ? might give indication of aerosol processing and/or sources Thermal desorption PTR-MS: detailed chemical composition Apply to aerosol filter samples taken in Cabauw, NL during Pegasos High volume filter samples: 500 l/min separate filters during day and night each loaded for 2-3 days High volume filter samples: 500 l/min separate filters during day and night each loaded for 2-3 days

3. 14 C for source apportionment Fossil fuel f m = 0 Biomass burning Biogenic f m = 1.1 - 1.2 f m ~ 1.04 14 C: radioactive isotope, continuously replenished in the atmosphere 14 C Measured on OC, EC, TC, WIOC using extraction technique developed at IMAU

4. 13 C indicator of aerosol processing? 12 C 13 C (~ 1%) More reactiveLess reactive Higher vapor pressureLower vapor pressure 2 stable carbon isotopes R= 13 C/ 12 C  -values: (R x -R st )/R st *1000 Photochemical aging: Oxidation by O 3, OH Loss of OC 12 C pref. reacted away Remaining carbon: Higher  13 C Gas phase formation of SV products: If gas phase precursors are partially reacted 12C pref. reacted to SV Products Lower  13 C

5. 13 C and chemical measurement setup Oven 1Oven 2 Catalysts 50-450°C 500°C Liquid N 2 Remove H 2 O CO 2 is frozen and later released to be analyzed for isotopic composition IRMS Isotope measurement PTR-MS High resolution mass spectrometry of largely unfragmented compounds

6. 2 cases 1) 24 - 27 MAY: Aged cont. case Warm Sunny dry Night: stable stratification low inversion layer 2) 1-3 JUNE: Recent pollution case cool sunny Night: stable stratification low inversion layer

7. Fossil and contemporary carbon in day and night contemporary OC concentration enhanced in the night

8. OC thermogram Aged cont. case Semi-volatile organics enhanced Low volatile organics little change

9.  13 C thermogram Aged cont. caseRecent poll case Consistent with partitioning: gas phase:  13 C low particle phase:  13 C high condensation lowers particle  13 C Other effects must play a role: Change in sources? day-time photochemistry? Recent SOA?

10. PTR-MS first results Lighter molecules preferentially enhanced during night time OC night / OC day

11. Summary Carbonaceous aerosol has higher fraction of contemporary carbon during night Mainly increase in contemporary OC, with small decrease in fossil OC and EC Oven 1Oven 2 50-450°C500°C Semi-volatile carbon is enhanced during night time IRMS Semi-volatile carbon depleted in  13 C compared to low-volatile (less aged?) Day-night change only at oven T=150 °C Compounds with smaller mass more strongly enhanced during the night

12. Outook IRMS Investigate isotopic effects of partitioning / photochemical aging in the lab Study source signatures Fall and winter studies Are O:C and H:C ratios higher during the night? Do any particular chemical compounds show a strong day/night difference (tracers?)

13. Outook B. Oyama, W. Ramon, P.A. de Wilde Grants: NWO grant number 820.01.001 ALW-­ ‐ Middelgroot program (Grant 834.08.002) Thanks for your attention