Heterogeneous Process Studies on the Formation of Secondary Aerosol

Transcription

1 2016 BC workshop Heterogeneous Process Studies on the Formation of Secondary Aerosol Maofa Ge Institute of Chemistry Chinese Academy of Sciences June

2 Aerosol Heterogeneous Chemistry Atmospheric oxidation VCs Cluster aging of aerosols N x, S 2 HN N x,s 2 N 2-3, S 2-3,S 2-4 Aerosol hygroscopicity Extinction properties Haze formation SA, Sulfate, Nitrate, Soot etc. hv Nucleation H 2 SA H, H 2 2, 3 Aerosol VCs SVCs

3 ICCAS Platform Physical & Atmospheric chemistry Radical chemistry PES-MS Gas (Radical) oxidation Surface interface Aerosol size DMA-CPC Gas phase chemistry & Photo-oxidation Smog chamber Gas-solid DRIFT-IR Matrix IR & Raman Gas-liquid VUV laser-ms PTR-MS particl esize Hygroscopicity Atmospheric chemistry 3 & Haze components online & long time simulations gas-aerosol measurements aerosol size, components, optics ptical Aerosol Chemical component CI-MS Aerosol ptical Property CRDS Aerosol Hygroscopicity H-TDMA

4 ICCAS Platform aerosol : size/components/optics EI-MS DRIFT-IR Flow Tube; Knudsen cell Raman Gas-solid/liquid reaction, kinetics cavity ring down spectrometry:aerosol extinction H-TDMA

5 Gas-solid kinetics: Mechanism S 2 (g) 3 (g) C 2 2 S 2 (g) k 1 k -1 CaC 3 (s) S 2 (ads) S 2 (ads) k 2 CaS 3 (ads) C 2 (g) S 2 (ads) S 3 2- (ads) S 4 2- (ads) CaS 3 (ads) 3 (g) k 3 CaS 4 (ads) 2 (g) Limiting cases : k k1k 2 k k d{s 4 } k1k 2 r [S 2] k[s 2] dt k k 1 2 k1k 2 k k k 1 2 (1) 当 k -1 <<k 2 时, k=k 1 ; K E RT d ln k RT d( 1 ) T d ln k d( 1 ) T a E a 1 The apparent activation energy :14.63 ± 0.20 kj/mol E a RT 2 k 1 k2 Kk2 k 1 d ln k 2 d ln( Kk2) RT RT d(1 ) d(1 ) T T (2) 当 k 2 <<k -1 时, ; K 2 d ln( K) RT d(1 ) T 2 d ln( k2) H d(1 ) T The balance between the two limiting cases can be used to interpret the turning point on the rate of sulfate formation. ads E a2

6 Gas-solid kinetics: Mechanism rganic acid on mineral dust Al H RCH k 1 k -1 Al H HCR Al H HCR Al Heterogeneous process: Important Atmospheric lifetime dust k 2 CR H 2 H HCH 8-13h 86 days CH 3 CH 4-5h 46days 4 SA SA=150 μm 2 cm -3

7 Gas-liquid Kinetics Diethylamine(DEA) Mass spectrum(vuv) Schematic diagram of experimental setup Rotating Wetted-Wall Flow Tube PIMS NIST:DEA MS (EI)

8 Gas-liquid Kinetics First-order rate k obs : ln S / S k L / v 0 obs Diffusion-limited rate k diff : k 3.66 D / r diff Surface rate constant k : 1/ k 1/ k 1/ k obs i 2 diff ave Reactive uptake coefficient: 4kV wa

9 Gas-liquid Kinetics Restrain diffusion Is possible! Radial diffusion Axial diffusion If The system Peclet Number sufficiently large the axial diffusion velocity will be much less than the flow velocity 25mm 6mm Radial diffusion Axial diffusion Pe = 2rv/D i ; Pe 10 is necessary, k diff = K d D i /r 2 (K d = 3.66 ) Radial diffusion The precondition: k obs < k diff /2 0.5< k obs /k <1 Carefully design!

10 Epoxide The uptake of two epoxides under different pressures : isoprene epoxide butadiene diepoxide H 2 S 4 P(Torr) ±1σ ( 10-5 ) ph= ± ±0.09 ph= ± ±0.15 Using rotating cylinder with inner radius of 8 mm for isoprene epoxide H 2 S 4 P(Torr) r = 12.5 mm k diff ±1σ ( 10-4 ) P(Torr) r = 8.0 mm k diff ±1σ ( 10-4 ) ph= ± ± wt % ± ± wt % ± ± 0.180

11 Role of H 2 2 : MB H 2 S 4 MB: 2-methyl-3-buten-2-ol H 2 S 4 H disappear C=C increase reactant GC: 5.778s (5.77s) 40wt%H 2 S 4 FTIR 40wt%H 2 S 4-1wt%H 2 2 混合溶液 H 2 S 4-1wt%H 2 2 H disappear,hc= formation C C GC: 5.264s (5.273s) IR/GC/MS; with H 2 2 : formation aldehyde and ketone; and polymerization; SVC and SA formation H

12 Role of H 2 2 : MB H 2 S 4 γ ~ γ ~ H 2 S 4 solution H 2 S 4 (1/4wt%)H 2 2 Uptake: increase 16 times!

13 Main route and product RH H 2 S 4 RHRR pathway A H 2 2 H heterolysis homolysis H2 2 H H H H 3 S- pathway B H Label experiments H H 2 S 4 H S 18 m/z=185-5 H H 2 H 2 S 4 HS 4 - H 3 S- 18 H H 18-3 S m/z=183 - H H 3 S 1 HS 4 - H 2 3 product ESI- MS VUV- TF-MS GC-MS GC-MS VUV-TF- MS IR 1 H 3 S 4 7 H Mechanism S 3 H H H 2 S 4 H 2 6 H H 2 H 2 S 4 H 2 2 H H H H H H2 H H H 2

14 New insights H gas H 18 H H 2 2 H H 2 S 4 H 3 S 1 RH--RH (main product) & RR 2 H experiments, confirm RH route 3 acetone 4 RR, SA H 3 S H2S4 H gas gas H H H 2 S 4 S 3 H H aqueous phase H 2 H 3 S 18 H H H gas gas

15 New insight RH source sink RH Atmospheric Chemistry Past present main H 2 R 2 3 alkene less By burning RH H 2S 4 H 2 2 RH RH RH RH hv Gas phase RH H RH 干 湿沉降 R 2 H 2 RS 3 H H 2 S 4 重排 小分子化合物 Liquid phase xidation S 2 Reaction with M Acetone N hv 3 H 2 H C hv H cycle CH 4 NHMCs gas phase H 2 2 H 2 R 2 hv H H 2 2 RH RR RH H 2 S 4 aqueous phase RH 2 RR R hv (main) (byproduct) 1 reduce H gas RH&RR, reenter gas phase Influence H radical RH Increase SA H 3 S H 3 S RS 3 H and RS 3 H, low volatility, SA

16 M Ge*, Atmos Environ, 2007, 2009, 2010, 2011, 2012, 2013 Smog chamber simulation Real atmospheric conditions Chamber 70L, 3000 L, 2X(5m 3 ) FEP Teflon film * Reaction rate * Mechanism

17 Atmospheric lifetime(eve/pve) τ=1/(k x [X]), x=h, N 3, 3, Cl concn/molecule cm -3 concn/molecule cm -3 k EVE /cm - 3 molecule -1 s -1 H h N h h Cl h k PVE /cm - 3 molecule -1 s -1 H h N h h Cl h τ τ

18 ICCAS-TRC (twin-reactor chamber) Smog chamber with various instruments for gas and particle measurements

19 Cavity ring down spectroscopy laser detector α ext L cd N D 4 2 ext ext NQ ext CRDS consists of two highly reflective concave mirrors with a reflectively of % The extinction coefficient is computed by comparing the decay time(τ) of a pulse laser trapped in the resonator both with and without aerosol to shot-to-shot :variations of the laser the absolute extinction of aerosol sample ; without instrument effective path length

20 Ammonium nitrate formation Smog chamber: RH<30%, rich NH 3 N 2, 3 and seed aerosol NH 4 N 3 increase continue 7 hour velocity (µg.m -3.h -1 ) N 3 - NH (6 obs.) 2.25 (4.5 obs.) Extinction Visibility ICCAS-TRC: SIA formation experiment

21 ICCAS-TRC:SA formation Yield (%) dum et al., 1996 (308K) Cocker et al., 2001 (293K) Takekawa et al., 2003 (303K) Song et al., 2005 (300K) Ng et al., 2007 (298K) This work (298K) simulation: Temp, RH, light source, VCs Low & High HC/Nx M o (ug/m 3 ) Advantage: Measure 2 chamber at the same time; Change : only single factor, M (ug/m3) Mass conc. for high HC/Nx Mass conc. for low HC/Nx t (h)

22 Photooxidation of aromatic hydrocarbons M (ug/m3) HC, 3 (ppb) HC 3 M M Corrected Diameter a Diameter (nm) Finding: Nx influence SA formation Low Nx: PM formation just after light on High Nx: PM formation need 2 h t (h) Fig a; low-nx experiment : 200 ppb m-xylene, 5 ppm H 2 2 Low-Nx experiments: H 2 2 was used as the H precursor. The background Nx level in the chamber : <1 ppb, the initial concentration of H 2 2 : 1 5 ppm. High-Nx : N 2 was introduced from a 50 ppm standard gas cylinder.

23 Photo-oxidation of aromatic hydrocarbons Qext Qext m-xylene SA RI=1.52 Ethylbenzene SA RI=1.478 Benzene SA RI=1.464 Toluene SA RI=1.45 a Diameter (nm) Benzene SA RI=1.496 Ethylbenzene SA RI=1.473 Toluene SA RI=1.464 m-xylene SA RI=1.464 b Dependence of the extinction efficiencies of the SA particles on the surface mean diameter at a wavelength of 532 nm and the retrieved RIs (a)low-nx (b) high-nx experiments Diameter (nm)

24 Photo-oxidation of aromatic hydrocarbons The RIs of the SAs are altered differently as the Nx concentration increases as follows: the RIs of the SAs derived from benzene and toluene increase, whereas those of the SAs derived from ethylbenzene and m-xylene decrease.

25 Photo-oxidation of aromatic hydrocarbons ULAQ MIRAGE ECHAM4, GCART, GISS, Sprintars and Grantour RIs of the different SA particles: comparison between experimental data & model values. The commonly used model values for the RIs of organic aerosols are generally higher than the experimental data for the SAs formed from VCs, which may cause the overestimation of direct radiative forcing of organic particles to a certain extent.

26 Photo-oxidation of aromatic hydrocarbons 1, The RIs of the BTEX SAs are closely related to the initial Nx concentration, with different aromatics displaying different trends. For the benzene and toluene SAs, the RI value increases as the Nx level rises, whereas for the ethylbenzene and m-xylene SAs, the RI value decreases correspondingly. This result is caused by the different molecular structures and the R 2 N pathway that occurs under the high-nx condition. 2, The dependence of the RI value on the initial hydrocarbon and oxidant concentrations was also investigated, revealing that the initial concentrations of these reagents have little influence on the optical properties of the SA. 3, For gas-phase oxidation with no seed particles, the BTEX SAs have no obvious absorption at 532 nm. However, the SA particles formed under other conditions may absorb light in the visible range, further studies should be performed.

27 Future Activities 1 Smog chamber experiments SA formation and extinction properties 2 Develop new techniques CIMS etc 3 BC Aerosol heterogeneous photochemistry

28 Acknowledgements Dr W. Wang, Dr. L. Du, Dr. S. Tong, Dr. L. Wang, Dr. L. Wu, Dr. Z. Liu, Dr. Q Liu, Dr. K Li, Fund: National Natural Science Foundation(NSFC) Chinese Academy of Sciences(CAS),