A. Even’s research while affiliated with Energy Research Centre of the Netherlands and other places

We tested the comparability of methods, in use in Europe, for measuring the concentration of aerosol-carbon. The study was performed in the framework of INTERCOMP2000, a field campaign organised in the first two weeks of April 2000 in the vicinity of the village of Melpitz, 45 km NE of Leipzig, Germany. Sampling of the aerosol took place with 19 samplers. Total carbon (TC) was measured with eleven methods and the mean concentration found for PM10 was close to 3 μg m −3 , of which 90% was in the PM2.5 fraction. Carbon and associated compounds constituted approximately 25% of the total aerosol mass in this fine fraction. Starting point of the evaluation of the data were the concentrations stemming from two identical PM2.5 high-volume samplers, of which the samples were analysed by four institutes. The daily values of TC were highly correlated and the (random) differences were of an absolute nature, with an overall standard deviation (SD) of 0.22 (±0.12) μg m −3 . This value for the SD is only twice that in the data of the individual institutes for a similar number of samples. In the series of four PM10 filter-samplers, the highest concentration was obtained with the sampler that collected the lowest amount per unit of surface area. This difference is indicative of an artefact caused by adsorption of gaseous carbon containing compounds. Evidence for such an adsorption artefact was provided by the presence of carbon in back-up filters, in amounts up to 20% of those of front filters. Adsorption can also be (part of) the explanation for a difference of 30% observed between concentrations obtained with filters and cascade impactors as samplers, because the latter collectors do not suffer from an adsorption artefact. Samples were also analysed for elemental carbon (EC). While differences of more than a factor of three between methods were observed, the correlation of the daily EC-concentrations over the period was high, better than 0.9 ( R 2 ). Two institutes analysed samples from filters and cascade impactors in the same way. Both observed that the EC-values from the filters were a factor of 1.4 higher than those from the impactors. Three methods were used to determine black carbon (BC) by optical means. Differences between the methods were large, but apparently of a systematic nature, because the correlation of the daily BC-values was very good. The correlation of daily BC and EC concentrations was also high.

A comprehensive range of aerosol parameters was measured at an urban and a rural site in the Milan, Italy metropolitan region during summer smog events in summer 1998. Measurements were performed as part of the Pianura Padana Produzione di Ozono (PIPAPO) field campaign to determine the sensitivity of O3 production to NOX and volatile organic carbon concentrations at several ground stations. Primary aerosol parameters (i.e., direct emissions) such as aerosol black carbon showed a distinct diurnal variation with maxima at about 0000 and 0800 central European summer time (CEST), in contrast to secondary aerosol parameters such as sulfate and nitrate. Aerosol number size distributions were measured under ambient conditions as well as after conditioning with volatility and hygroscopicity systems. A mode at d = 20–30 nm in the number concentration was found at 0800 CEST and exhibited high volatility at 110�C (�80% volume lost upon heating) but no hygroscopic behavior. Based on these measurements, small particles (d < 40 nm) are thought to consist mainly of hydrophobic particulate organic matter, rather than soot or H2SO4 aerosols. Two distinct hygroscopic modes with average growth factors d/d0 � 1.02 and 1.21–1.28 were found for particles with dry (relative humidity of <30%) diameters d0 = 50–200 nm. Submicrometer aerosols exhibited lower volatility at the rural than at the urban site, which is attributed to additional particulate mass produced by secondary particle formation.

IPPC reports the aerosol radiative forcing per major aerosol category, like sulphate and fossil fuel derived carbon. Part of this carbon is reflective and part of the material (black carbon "soot") absorbs radiation. We find that in the Netherlands sulphate contributes some 30% to the reflection. Nitrate contributes even more; an estimated 35%. The local importance of nitrate is acknowledged in the new IPCC-TAR, but it is stated that insufficient data exist to assess its importance outside of the Netherlands. The amount of "fossil fuel" carbon could not be directly quantified. The reason is that it consists of thousands of different chemical compounds that all have different physicochemical properties. However, by deduction we found that its concentration is substantial. The mentioned three components, nitrate, sulphate and carbon, are thus the dominant aerosol components in the regional aerosol radiative forcing. As can be seen in the results, the forcing on partly cloudy days seems less because of a shorter sunshine duration. It should then be considered that on cloudy days the reflective power of the aerosol is higher due to the higher relative humidity and the associated uptake of water by the aerosol. This compensates for the shorter sunshine duration. Reflection of solar radiation caused by the aerosol is exerted by aerosol components that can be of a natural origin or produced by man. In our report we show, on the basis of the aerosol composition, that at least 85% of the aerosol is of a manmade origin and the aerosol reflection is therefore a forcing. The forcing is defined as the amount of solar radiation reflected back into space, and not available for heating of the earth due to the presence of manmade aerosol.