. Source apportionment using the bilinear model through a multilinear engine (ME-2) was successfully applied to non-refractory organic aerosol (OA) mass spectra collected during the winter of 2011 and 2012 in Zurich, Switzerland using the aerosol chemical speciation monitor (ACSM). Five factors were identified: low-volatility oxygenated OA (LV-OOA), semivolatile oxygenated OA (SV-OOA), hydrocarbon-like OA (HOA), cooking OA (COA) and biomass burning OA (BBOA). A graphical user interface SoFi (Source Finder) was developed at PSI in order to facilitate the testing of different rotational techniques available within the ME-2 engine by providing a priori factor profiles for some or all of the expected factors. ME-2 was used to test the positive matrix factorization (PMF) model, the fully constrained chemical mass balance (CMB) model, and partially constrained models utilizing a values and pulling equations. Within the set of model solutions determined to be environmentally reasonable, BBOA and SV-OOA factor mass spectra and time series showed the greatest variability. This variability represents the uncertainty in the model solution and indicates that analysis of model rotations provides a useful approach for assessing the uncertainty of bilinear source apportionment models.

/pdf/sofi-an-igor-based-interface-for-the-efficient-use-of-the-5f5h07tgig.pdf

SoFi, an IGOR-based interface for the efficient use of the generalized multilinear engine (ME-2) for the source apportionment: ME-2 application to aerosol mass spectrometer data

. PM1 (particulate matter with an aerodynamic diameter This paper presents a method for estimating cooking organic aerosol in ambient datasets based on the fractions of organic mass fragments at m/z 55 and 57: their data points fall into a V-shape in a scatter plot, with strongly influenced HOA data aligned to the right arm and strongly influenced COA data points aligned to the left arm. HR data show that this differentiation is mainly driven by the oxygen-containing ions C3H3O+ and C3H5O+, even though their contributions to m/z 55 and 57 are low compared to the reduced ions C4H7+ and C4H9+. A simple estimation method based on the markers m/z 55, 57, and 44 is developed here and allows for a first-order-estimation of COA in urban air. This study emphasizes the importance of cooking activities for ambient air quality and confirms the importance of chemical composition measurements with a high mass and time resolution.

/pdf/identification-and-quantification-of-organic-aerosol-from-46ayqyt4zt.pdf

Identification and quantification of organic aerosol from cooking and other sources in Barcelona using aerosol mass spectrometer data

. The absorption Angstrom exponent (AAE) of externally mixed black carbon (BCExt), or BC internally mixed with non-absorbing material (BCInt), is often used to determine the contribution of brown carbon (BrC) light absorption at short visible wavelengths. This attribution method contains assumptions with uncertainties that have not been formally assessed. We show that the potential range of AAE for BCExt (or BCInt) in the atmosphere can reasonably lead to +7% to −22% uncertainty in BCExt (or BCInt) absorption at short wavelengths derived from measurements made at longer wavelengths, where BrC is assumed not to absorb light. These uncertainties propagate to errors in the attributed absorption of BrC. For uncertainty in attributed BrC absorption to be ≤ ± 33%, 23% to 41% of total absorption must be sourced from BrC. These uncertainties would be larger if absorption by dust were also to be considered due to additional AAE assumptions. For data collected during a biomass-burning event, the mean difference between measured and AAE attributed BrC absorption was found to be 34% – an additional uncertainty in addition to the theoretical uncertainties presented. In light of the potential for introducing significant and poorly constrained errors, we caution against the universal application of the AAE method for attributing BrC absorption.

/pdf/on-the-attribution-of-black-and-brown-carbon-light-efzo4ub0vp.pdf

On the attribution of black and brown carbon light absorption using the Ångström exponent

. Equivalent black carbon (EBC) measured by a multi-wavelength Aethalometer can be apportioned to traffic and wood burning. The method is based on the differences in the dependence of aerosol absorption on the wavelength of light used to investigate the sample, parameterized by the source-specific absorption Angstrom exponent (α). While the spectral dependence (defined as α values) of the traffic-related EBC light absorption is low, wood smoke particles feature enhanced light absorption in the blue and near ultraviolet. Source apportionment results using this methodology are hence strongly dependent on the α values assumed for both types of emissions: traffic αTR, and wood burning αWB. Most studies use a single αTR and αWB pair in the Aethalometer model, derived from previous work. However, an accurate determination of the source specific α values is currently lacking and in some recent publications the applicability of the Aethalometer model was questioned. Here we present an indirect methodology for the determination of αWB and αTR by comparing the source apportionment of EBC using the Aethalometer model with 14C measurements of the EC fraction on 16 to 40 h filter samples from several locations and campaigns across Switzerland during 2005–2012, mainly in winter. The data obtained at eight stations with different source characteristics also enabled the evaluation of the performance and the uncertainties of the Aethalometer model in different environments. The best combination of αTR and αWB (0.9 and 1.68, respectively) was obtained by fitting the Aethalometer model outputs (calculated with the absorption coefficients at 470 and 950 nm) against the fossil fraction of EC (ECF ∕ EC) derived from 14C measurements. Aethalometer and 14C source apportionment results are well correlated (r  =  0.81) and the fitting residuals exhibit only a minor positive bias of 1.6 % and an average precision of 9.3 %. This indicates that the Aethalometer model reproduces reasonably well the 14C results for all stations investigated in this study using our best estimate of a single αWB and αTR pair. Combining the EC, 14C, and Aethalometer measurements further allowed assessing the dependence of the mass absorption cross section (MAC) of EBC on its source. Results indicate no significant difference in MAC at 880 nm between EBC originating from traffic or wood-burning emissions. Using ECF ∕ EC as reference and constant a priori selected αTR values, αWB was also calculated for each individual data point. No clear station-to-station or season-to-season differences in αWB were observed, but αTR and αWB values are interdependent. For example, an increase in αTR by 0.1 results in a decrease in αWB by 0.1. The fitting residuals of different αTR and αWB combinations depend on ECF ∕ EC such that a good agreement cannot be obtained over the entire ECF ∕ EC range using other α pairs. Additional combinations of αTR  =  0.8, and 1.0 and αWB  =  1.8 and 1.6, respectively, are possible but only for ECF ∕ EC between  ∼  40 and 85 %. Applying α values previously used in the literature such as αWB of  ∼  2 or any αWB in combination with αTR  =  1.1 to our data set results in large residuals. Therefore we recommend to use the best α combination as obtained here (αTR  =  0.9 and αWB  =  1.68) in future studies when no or only limited additional information like 14C measurements are available. However, these results were obtained for locations impacted by black carbon (BC) mainly from traffic consisting of a modern car fleet and residential wood combustion with well-constrained combustion efficiencies. For regions of the world with different combustion conditions, additional BC sources, or fuels used, further investigations are needed.

/pdf/evaluation-of-the-absorption-angstrom-exponents-for-traffic-1qq41rjye2.pdf

Evaluation of the absorption Ångström exponents for traffic and wood burning in the Aethalometer-based source apportionment using radiocarbon measurements of ambient aerosol

An overview of particulate emissions from residential biomass combustion

. The contributions of fossil fuel (FF) and wood burning (WB) emissions to black carbon (BC) have been investigated in the recent past by analysis of multi-wavelength aethalometer data. This approach utilizes the stronger light absorption of WB aerosols in the near ultraviolet compared to the light absorption of aerosols from FF combustion. Here we present 2.5 years of seven-wavelength aethalometer data from one urban and two rural background sites in Switzerland measured from 2008–2010. The contribution of WB and FF to BC was directly determined from the aerosol absorption coefficients of FF and WB aerosols which were calculated by using confirmed Angstrom exponents and aerosol light absorption cross-sections that were determined for all sites. Reasonable separation of total BC into contributions from FF and WB was achieved for all sites and seasons. The obtained WB contributions to BC are well correlated with measured concentrations of levoglucosan and potassium while FF contributions to BC correlate nicely with NOx. These findings support our approach and show that the applied source apportionment of BC is well applicable for long-term data sets. During winter, we found that BC from WB contributes on average 24–33 % to total BC at the considered measurement sites. This is a noticeable high fraction as the contribution of wood burning to the total final energy consumption is in Switzerland less than 4 %.

/pdf/a-2-5-year-s-source-apportionment-study-of-black-carbon-from-7mw3d2g4x0.pdf

A 2.5 year's source apportionment study of black carbon from wood burning and fossil fuel combustion at urban and rural sites in Switzerland

/pdf/a-two-year-s-source-apportionment-study-of-wood-burning-and-4w3vhp9fo1.pdf

A two year's source apportionment study of wood burning and traffic aerosols for urban and rural sites in Switzerland

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A 2.5 year's source apportionment study of black carbon from wood burning and fossil fuel combustion at urban and rural sites in Switzerland

A two year's source apportionment study of wood burning and traffic aerosols for urban and rural sites in Switzerland