Source apportionment of submicron organic aerosols at an urban site by linear unmixing of aerosol mass spectra

Transcription

1 Source apportionment of submicron organic aerosols at an urban site by linear unmixing of aerosol mass spectra V. A. Lanz 1, M. R. Alfarra, U. Baltensperger, B. Buchmann 1, C. Hueglin 1, and A. S. H. Prévôt [1] Empa, Swiss Federal Laboratories for Materials Testing and Research, Laboratory for Air Pollution and Environmental Technology, CH-8 Duebendorf, Switzerland [] PSI, Paul Scherrer Institute, Laboratory for Atmospheric Chemistry, CH- 53 Villigen PSI, Switzerland submitted to ACPD Materials Science & Technology Measurement campaign N urban background site (Zurich - Kaserne) three-week measurement period in summer 5

2 Positive matrix factorization (PMF) X = G F species j: 1 m Columns (scores) samples in time i: 1 n X {n x m} = G {n x p} F {p x m} Rows (loadings or factors) number of p must be specified - non-negativity of G and F - algorithm accounts for uncertainty in X (weighted least squares) Number of factors p? R max(rotmat) x number of factors Goodness of fit (R ) of regressed scores vs. measured organics and rotational freedom as a function of the number of factors chosen in PMF.

3 Most important step in PMF analyses: interpretation of F (and G), i.e. the mathematical solutions (G and F matrices) must be linked to sources and aerosol components rows of F - factors: e.g check for spectral similarity with ~ AMS reference spectra columns of G - scores: e.g. look at correlation with other species (time series) (compare modelled emission/ratios with literature) Interpretation of F factors spectral similarity to reference spectra R : correlation of all s R > : correlation of > ms norm. i = ms / ms i = i i i factor [norm. int] Ref. MS [norm. int] similarity measure for AMS spectra?

4 Interpretation of F factors example 1: 1 st factor is very similar to fulvic acid, (aged urban aerosol, ) (R =.9; R > =.83) interpretation as OOA (oxygenated organic aerosol) example : 3 rd factor is very close to fuel, (lubricant oil, diesel, ) (R =.99; R > =.99): interpretation as HOA (hydrocarbon-like organic aerosol)

5 Interpretation of G - scores AMS particle-sulphate [µg m -3 ] OOA, type I [µg m -3 ] correlation with other species -secondary processes: atm. oxidants (O 3 + NO ) temperature particle-phase nitrate/sulfate -primary processes: carbon monoxide (CO) nitrogen oxides (NO x ) elemental carbon (EC) 1 8 temperature [ C] AMS particle-nitrate [µg m -3 ] dat OOA, type II [µg m -3 ] HOA [µg m -3 NO x [ppb] ] charbroiling [µg m -3 ] wood burning [µg m -3 ] CO [ppm] minor source (cooking) [µg m -3 ] modelled emission ratios emission ratio [ng m -3 /ppbv] Zürich- Kaserne Pittburgh (Zhang et al., 5) New England (de Gouw et al., 5) Tokyo (Takegawa et al., 5) diesel trucks/light-duty vehicles (calculated from Kirchstetter et al., 1999) POA/CO HOA/NO x /1 AMS (PMF) AMS (-fact. approach) total OA, gasphase tracer AMS (-fact. approach) tunnel studies

6 Main results SOA and POA estimation PM 1 (Zürich-Kaserne, Summer 5) 1% wood burning 13% in Zürich, ( 1 C analysis, Szidat et al., ) OOA, type II (volatile); % charbroiling; 11% wood burning ; 1% SOA % POA 3% fossil fuel; 7% OOA, type I (aged); % minor source (cooking); % (avg. OM.58 µg m -3 )

7 Limitations of PMF PMF (and other multivariate receptor models) cannot resolve sources/components when (a) (b) profiles are too similar when sources/components show similar temporal variation (e.g. Zurich winter data set) CMB approach (collinearity and multicollinearity of profiles might be a problem) Hybrid model combining CMB and PMF features? Outlook: CMB - type approach (Zurich winter) (diesel) [µg m -3 ] (oxygenated) [µg m -3 ] (wood burning) [µg m -3 ] dat Temporal variation of three mass tracers (, 57 and ) during the Zurich winter campaign

8 Outlook: CMB - type approach (Zurich winter) Sources (F) known: X F + = GF F + G X (w) {F (s) } + = G (w) F (s) {F (s) } + G (w) G (w) 95%-c.i. = X(w) 95%-c.i. {F(s) } + 95%-c.i. F + the pseudo-inverse of F w: winter, s: summer propagating uncertainty measurement uncertainty model uncertainty Outlook: CMB - type approach (Zurich winter) preliminary! calculated G factors % 5% average contribution (incl. uncertainty estimates) % 3% % 1% % OOA HOA wood burning aerosol

9 Calculated factors and its interpretation Spectra of all PMF factors (interpreted as the denoted source profiles) calculated by -factorial PMF. Only for the minor source the full mass range up to 3 is shown because it is the only source or component with significant features in the high mass region on the linear scale OOA, type I OOA, type II HOA charbroiling x1-3 wood burning x minor source (food cooking)

10 1 8 measured submicron sulphate [µg m -3 ] modelled wood burning aerosol [µg m -3 ] : : 18: :.8.5 : 1: Date and Time Measured AMS-sulphate and modelled aerosol from wood burning on the Swiss national holiday (1 August)