Intercomparison of standard and capture vaporizer in aerosol mass spectrometer (AMS)

Transcription

1 Intercomparison of standard and capture vaporizer in aerosol mass spectrometer (AMS) Weiwei Hu 1, Pedro Campuzano-Jost 1, Douglas A. Day 1, Philip Croteau 2, Manjula R. Canagaratna 2, John T. Jayne 2, Douglas R. Worsnop 2, Jose L. Jimenez 1 1 CIRES and Dept. of Chemistry, University of Colorado at Boulder, Boulder, CO, USA 2 Aerodyne Research, Inc., Billerica, Massachusetts, USA 1

2 Feature of standard vaporizer (SV) vs capture vaporizer (CV) SV Porous Tungsten CV Solid Molybdenum edge Species: Organic aerosol, Sulfate Standard vaporizer temperature (T v ): 600 Collection efficiency (CE) depends on : Chemical composition: e.g. NH 4 NO 3 fractions, Acidity of aerosol Aerosol phase: e.g. Solid/semisolid/liquid particle, Relative humidity Typically contribute the most uncertainty for ambient aerosol measurement Middlebrook et al., AST,

3 Outlook of SV and CV 3

4 Temperature measurement for CV Hu et al., submitted

5 Experiment setup: (a) Bypass pump Lab Nafion dryer or silica gel Atomizer SMPS CPC AMS with SV AMS with CV Bypass pump (b) Other sampling line AMS with SV Ambient P PM 2.5 cyclone Nafion dryer Nafion dryer AMS with CV Flow reactor Nafion dryer Only exist in SOAS study SMPS CPC Bypass 5

6 Lab Ambient Outline Does capture vaporizer make CE~1? Gas-phase CO 2 (g) formation in CV Does the capture vaporizer preserve or diminish the chemical and physical information from AMS? Fragmentation and OA source identification? Size distributions? 6

7 Lab CE of standard inorganic species CE=AMS/CPC mass ratio NH 4 NO 3 NaNO 3 (NH 4 ) 2 SO 4 NH 4 Cl An improvement in CE of inorganic species in the CV Shown results are carried out under medium vaporizer temperature C Hu et al., submitted

8 Lens transimission corrections for NaNO 3 d m =300nm d va =670 nm Hu et al., submitted

9 Ambient CE of ambient aerosols SV: CE: CV: CE=1 Hu et al., in prep

10 Ambient Multiple results support ambient CE in CV =1 SV: CDCE= SV vs CV CV: CE=1 AMS vs SMPS Total OA SO 4 NO 3 NH 4 CV SV Hu et al., in prep

11 Evaluation on chemical composition CE correction Hu et al., in prep

12 Lab Ambient Outline Does capture vaporizer make CE~1? Gas-phase CO 2 (g) formation in CV Does the capture vaporizer preserve or diminish the chemical and physical information from AMS? Size distributions? Fragmentation and OA source identification? 12

13 Production of CO 2 (g) is negligible for the CV for NH 4 NO 3 and comparable to the SV for NaNO 3. Hu et al., submitted

14 Lab Ambient Outline Does capture vaporizer make CE~1? Gas-phase CO 2 (g) formation in CV Does the capture vaporizer preserve or diminish the chemical and physical information from AMS? Fragmentation and OA source identification? Size distributions? 14

15 Lab Fragmentation pattern of inorganic NH 4 NO 3 SV CV Hu et al., submitted Inorganic does not evaporate as intact salts E.g., NH 4 NO 3 (s) NH 4 NO 3 (g) but go through thermal decomposition. E.g., NH 4 NO 3 (s) NH 3 (g)+hno 3 (g); HNO 3 (g) NO 2 (g)+h 2 O(g)+O 15 2 (g) (Drewnick et al., 2015)

16 Lab Fragmentation pattern of organic species C x H y+ C x H y O + Squalene C 30 H 50 C x H y+ C x H y O + C x H y O + 2 Citric acid C 6 H 8 O 7 Hu et al., in prep Thermal decomposition is LARGER in CV (esp, for oxidizes species)! 16 CO enhancement

17 Fragmentation pattern of organic species C x H y+ C x H y O + C x H y O + 2 Oleic acid C 18 H 34 O 2 CV Thermal decomposition is LARGER in CV (esp, for oxidizes species)! CO enhancement 17

18 Lab Where CO ion came from? Measured isotope C13 labeled oleic acid 18

19 Lab PToF show CO peak similar with aerosol phase j13c 3 H + 5 j13co + j13co + 2 CO in aerosol PToF CO 2 in aerosol PToF Squalene Oleic acid Citric acid DOS Chamber SOA Isotopelabeled Oleic acid 19

20 Lab Ambient Chemical information in CV is not lost F 44 =CO 2 /OA Hu et al., in prep

21 CV Ambient Ambient elemental ratio comparison Hu et al., in prep SV 21

22 Ambient Similar PMF results for SV vs CV IEPOX-SOA: Isoprene epoxydiols-derived SOA SV CV Hu et al., in prep

23 Lab Ambient Outline Does capture vaporizer make CE~1? Gas-phase CO 2 (g) formation in CV Does the capture vaporizer preserve or diminish the chemical and physical information from AMS? Fragmentation and OA source identification? Size distributions? 23

24 Lab Size-resolved detection of inorganic ions SV CV Hu et al., submitted

25 Ambient Size distribution of ambient aerosol in CV still work Total SO 4 NO 3 NH 4 SV CV Hu et al., in prep

26 Temperature dependent size distribution Hu et al., submitted

27 Estimating vaporizer temperature for detecting species in size mode Hu et al., submitted

28 SV CV CE for ambient particles CDCE CE=1 CE for pure inorganics in lab Bounce <1 but better than SV Impact of thermal decomposition CE ~1 for ambient particles Information for source apportionment (PMF) Excellent Better So-So Bad Longer residence time Substantial at high OA loading Organic nitrate vs. ammonium nitrate Low S/N OA elemental ratios Single particle calibration CPC-based calibration Heater bias dependence of signal Sensitive Not sensitive Nitrate Chloride artifact Vary with instrument history Vary with instrument history CO 2 signal decay lifetime CO 2 (g) formation from nitrates Lab & Chamber size distribution Ambient size distribution SO 4 UMR quantification under high OA For SO 3+ and HSO 3 + ions faster than SV Minor for AN, comparable for SN For monodisperse particles Need AS calibration 28

29 Faster CO 2 decay in CV than SV Citric acid C 6 H 8 O 7 τ CO2 11s τ CO2 <3s 29

30 Summary CE ~1! Slower evaporation impacts size distributions Still OK for ambient air. Much broader for monodisperse lab exp. CO 2 formation was neg Production of CO 2 (g) is negligible for the CV for NH 4 NO 3 and comparable to the SV for NaNO 3. Mass spectra shifted to smaller fragments. But information content (e.g. OA sources and elemental ratios) not lost!! Further analysis: CO formation influences to the quantification of OA. Thanks for your attention. 27