On the nonlinear relation between the Coefficient of Haze and Elemental Carbon mass concentration.

Coefficient of Haze (CoH) was the official proxy for the mass concentration of particulate matter in the US from ca. 1950 onwards. Originally, a linearity between CoH and sample load was claimed, but although shortly after the introduction of the method it was found that the relation between mass loading and the fraction of light 10 absorbed by the sample was identical to the nonlinear curve of the European "Black Smoke" (BS) method this correction was not officially adopted. We found that BS is a linear proxy for Elemental Carbon (EC) enabling an easy nonlinear conversion of CoH to EC concentration. Earlier it had been assumed that light-absorption by a sample is equal in the two methods, although CoH is obtained by light transmission while BS by light reflection. The "Filter Smoke Number" (FSN), used for diesel-soot emissions, is in essence the light-absorption by samples collected on the same filter type as in the CoH method (but probed in reflection). We noticed that the curve relating load and FSN is indistinguishable from the BS/EC curve. Ingram showed that light-absorption measured in reflection and transmission for this filter type is highly similar, so the standard BS/EC curve can be used to compare BS/EC and CoH. At low loadings the relation of EC concentration and CoH was quite similar to the equivalency factor of Black Carbon (BC) concentration and CoH. At CoH = 8, the historic limit of a severe smog day; however, the EC/BC-concentration alone was three times higher than that based on a (linear) equivalency factor. At CoH = 8, EC/BC mass concentrations alone reached the OSHA 8-hr workplace exposure limit of 150 µg m-3 for total carbon (the sum of organic carbon (OC) and EC).Implications: In this MS we show that the historic database of Coefficient of Haze (CoH) data can be converted to Elemental Carbon (EC) concentrations via several steps involving other historic and current measurement techniques (the European Black Smoke (BS) technique and techniques to measure Black Carbon (BC) and EC). The originally claimed linear relation between CoH and sample load is in reality a strongly nonlinear relation, so using the original linear relation leads to severe underestimations of historic EC concentrations especially on days with high concentrations of EC.

Dependence of home outdoor particulate mass and number concentrations on residential and traffic features in urban areas.

The associations between residential outdoor and ambient particle mass, fine particle absorbance, particle number (PN) concentrations, and residential and traffic determinants were investigated in four European urban areas (Helsinki, Athens, Amsterdam, and Birmingham). A total of 152 nonsmoking participants with respiratory diseases, not exposed to occupational pollution, were included in the study, which comprised a 7-day intensive exposure monitoring period of both indoor and home outdoor particle mass and number concentrations. The same pollutants were also continuously measured at ambient fixed sites centrally located to the studied areas (fixed ambient sites). Relationships between concentrations measured directly outside the homes (residential outdoor) and at the fixed ambient sites were pollutant-specific, with substantial variations among the urban areas. Differences were more pronounced for coarse particles due to resuspension of road dust and PN, which is strongly related to traffic emissions. Less significant outdoor-to-fixed variation for particle mass was observed for Amsterdam and Birmingham, predominantly due to regional secondary aerosol. On the contrary, a strong spatial variation was observed for Athens and to a lesser extent for Helsinki. This was attributed to the overwhelming and time-varied inputs from traffic and other local sources. The location of the residence and traffic volume and distance to street and traffic light were important determinants of residential outdoor particle concentrations. On average, particle mass levels in suburban areas were less than 30% of those measured for residences located in the city center. Residences located less than 10 m from a street experienced 133% higher PN concentrations than residences located further away. Overall, the findings of this multi-city study, indicated that (1) spatial variation was larger for PN than for fine particulate matter (PM) mass and varied between the cities, (2) vehicular emissions in the residential street and location in the center of the city were significant predictors of spatial variation, and (3) the impact of traffic and location in the city was much larger for PN than for fine particle mass.