H.M. ten Brink

Anthropogenic black carbon and fine aerosol distribution over Europe

We present a model simulation for the year 1995 accounting for primary particles, which are an important component of fine aerosols over Europe. A new emission inventory for black carbon, (BC) was developed on the basis of the recent European emission inventory of anthropogenic primary particulate matter (Coordinated European Programme on Particulate Matter Emission Inventories, Projections and Guidance (CEPMEIP)). The annual BC emissions of Europe and the former Soviet Union for 1995 are estimated at 0.47 and 0.26 Tg C, respectively, with highest contributions from transport (off-road and on-road) and households. Modeled BC concentrations range from ≤0.05 μtg/m 3 in remote regions to more than 1 μtg/m3 over densely populated areas. The modeled BC concentration is about 25% of the total primary aerosol concentration. The primary aerosol fields were combined with previously calculated secondary aerosol concentrations to obtain an estimate of the total anthropogenic fine aerosol distribution. Modeled BC levels contribute only 4 10% to fine aerosol mass, whereas sulphate and nitrate contribute 25-50 and 5-35%, respectively. Comparison with experimental data revealed that the model underestimates PM2.5 levels, mostly caused, by the underprediction of total carbonaceous material (BC and OC) by a factor of e12. The underestimation can partly be explained by the influence of local emissions, measurement uncertainties, natural sources, and representation of wet deposition. However, the uncertainties associated with the emission inventory for BC (and total PM) may be the most important cause for the discrepancy. In comparison with previous studies, our BC emission estimate is a factor of 2 lower, caused by the choice of more recent emission factors. Therefore a better knowledge of emission factors is urgently needed to. estimate the BC (and PM) emissions reliably. Copyright 2004 by the American Geophysical Union.

Modal character of atmospheric black carbon size distributions

Samples of atmospheric aerosols, collected with cascade impactors in the urban area of Vienna (Austria) and at a coastal site on the North Sea, were investigated for black carbon (BC) as the main component of absorbing material and for mass. The size distributions are structured. The BC distributions of these samples show a predominant mode, the accumulation aerosol, in the upper submicron size range, a less distinct finer mode attributable to fresh emissions from combustion sources, and a distinct coarse mode of unclear origin. It is important to note that some parameters of the accumulation aerosol are related statistically, indicating the evolution of the atmospheric accumulation aerosol.

Composition/size of the light-scattering aerosol in the Netherlands

In 1992, 1993 and 1994 the size/composition of the aerosol in The Netherlands was measured in several measuring campaigns. The central aim of the study was the characterisation of those anthropogenic particles which most effectively scatter short-wave solar radiation. Since the largest effect of aerosol on radiation was expected at the times with the highest radiative flux, the measurements were made in the summer half-year around midday and under sunny conditions. Aerosol in arctic marine air served as the reference background. It contained as little as 0.l gm m−3 nitrate and non-sea-salt sulphate. In continental air some 75% of the aerosol mass was submicron. Ammonium nitrate and ammonium sulphate were the dominant (anthropogenic) aerosol species in the size range with maximum light-scattering (0.4–1.0 gm) and, with values up to 25 gmm−3, almost completely of a manmade origin. The ammonium nitrate concentrations were as high as or higher than those of ammonium sulphate, while the concentration of ammonium nitrate may have been underestimated because of evaporative losses during collection, of which examples are given. The sulphate size distribution was very similar to that in the period 1982–1984, which is indicative of stability of the distribution over time. Almost half of the submicron aerosol in the relevant size range could not be identified. Elemental-carbon contributed only an estimated 10% to this mass and the submicron dust content was even smaller. It was thus concluded by inference that most of the unidentified material was organic carbon. In marine air advected over the U.K. the submicron aerosol was manmade. In the particles which most effectively scatter solar radiation natural sea-salt-chloride is substituted by manmade sulphate. This substitution greatly changes the aerosol (radiative) properties: laboratory investigations, performed as part of this study, showed that sodium sulphate is a water-free crystal, while the original sea-salt aerosols are metastable saline droplets.

Aerosol light-scattering in The Netherlands

The relation between the (midday) aerosol light-scattering and the concentrations of nitrate and sulfate has been assessed at a site near the coast of the North Sea in The Netherlands. Midday was selected for the measurements because this is the time at which the aerosol is most effective in the scattering of solar radiation. Automated thermodenuders were used for the hourly measurement of the concentration of nitrate and sulfate with a lower detection limit of 0.1 μ m−3. The site is operational since October 1993. The first-year average dry aerosol light-scattering (measured with an integrating nephelometer at a wavelength of 525 nm) was 0.71 × 10−4 mImage . In arctic marine air the aerosol light-scattering was a factor of 10 lower than the average value, in polluted continental air it was up to a factor of 10 higher. The ratio of the total aerosol light-scattering to the concentration of sulfate was 20 m2 g−1. The contribution of nitrate to the aerosol light-scattering was higher than that of sulfate in the winter and of about equal magnitude in the summer period. In November and December of 1993, the humidity dependence of the aerosol light-scattering was investigated. Two types of (continental) aerosol were found with respect to the humidity behavior. One type showed a significant increase in light-scattering at the deliquescence points of ammonium nitrate and ammonium sulfate, with that of ammonium nitrate the most pronounced. The second type of continental aerosol did not show deliquescence, but followed the typical humidity dependence of aerosol in a supersaturated droplet state. In this latter aerosol type, nitrate dominated over sulfate. It was concluded from the study that the aerosol light-scattering in The Netherlands, in particular its humidity dependence, is governed by (ammonium) nitrate.

Intercomparison of near real time monitors of PM2.5 nitrate and sulfate at the U.S. Environmental Protection Agency Atlanta Supersite

[1] Five new instruments for semicontinuous measurements of fine particle (PM2.5) nitrate and sulfate were deployed in the Atlanta Supersite Experiment during an intensive study in August 1999. The instruments measured bulk aerosol chemical composition at rates ranging from every 5 min to once per hour. The techniques included a filter sampling system with automated water extraction and online ion chromatographic (IC) analysis, two systems that directly collected particles into water for IC analysis, and two techniques that converted aerosol nitrate or sulfate either catalytically or by flash vaporization to gaseous products that were measured with gas analyzers. During the one-month study, 15-min integrated nitrate concentrations were low, ranging from about 0.1 to 3.5 μg m -3 with a mean value of 0.5 μg m -3 . Ten-minute integrated sulfate concentrations varied between 0.3 and 40 μg m -3 with a mean of 14 μg m -3 . By the end of the one-month study most instruments were in close agreement, with r-squared values between instrument pairs typically ranging from 0.7 to 0.94. Based on comparison between individual semicontinuous devices and 24-hour integrated filter measurements, most instruments were within 20-30% for nitrate (∼0.1-0.2 μg m -3 ) and 10-15% for sulfate (1-2 leg m -3 ). Within 95% confidence intervals, linear regression fits suggest that no biases existed between the semicontinuous techniques and the 24-hour integrated filter measurements of nitrate and sulfate;, however, for nitrate, the semicontinuous intercomparisons showed significantly less variability than intercomparisons amongst the 24-hour integrated filters.

Anthropogenic and natural constituents in particulate matter in the Netherlands

To develop mitigation strategies for reducing concentrations of both PM2.5 and PM10, the origin of particulate matter (PM) needs to be established. An intensive, one-year measurement campaign from August 2007 to August 2008 was carried out to determine the composition of PM 10 and PM2.5 at five locations in the Netherlands, aiming at reducing the uncertainties on the origin of PM. Generally, a considerable conformity in the chemical composition of PM 2.5 (and PM10) is observed. From all constituents present in PM 2.5, the secondary inorganic aerosol is the most dominant (42– 48%), followed by the total carbonaceous matter (22–37%). Contributions from sea salt (maximum 8%), mineral dust and metals (maximum 5%) are relatively low. For the first time, a detailed overview of the composition of the coarse fraction can be presented. Compared to the fine fraction, contributions of sea salt, mineral dust and metals are larger resulting in a more balanced distribution between the various constituents. Through mass closure a considerable part of the PM mass could be defined (PM 2.5: 80–94%). The chemical distribution on days with high PM levels shows a distinct increase in nitrate as well as in the unaccounted mass. Contributions of the other constituents remain equal or are lower (sea salt) when expressed in percentages. A correspondence between nitrate and the unaccounted mass is observed hinting at the presence of water on the filters. The contribution from natural sources in the Netherlands (at a rural station) was estimated to be 19 to 24% for PM 10 and 13 to 17% for PM2.5. Correspondence to: E. P. Weijers (weijers@ecn.nl)

Nephelometer derived and directly measured aerosol optical depth of the atmospheric boundary layer

Abstract The aerosol optical depth of the atmospheric boundary layer was determined both from direct solar irradiance measurements and from vertical extrapolation of ground-based nephelometry, during a period with cloudless skies and high aerosol mass loadings in the Netherlands. The vertical profile of the aerosol was obtained from lidar measurements. From humidity controlled nephelometry at the ground and humidity profiles from soundings, the scattering aerosol extinction as a function of height was assessed. Integration of the extinction over the aerosol layer gave the aerosol optical depth of the atmospheric boundary layer. This optical depth at the narrow band of the nephelometer was translated to a spectrally integrated value, assuming an Angstrom wavelength exponent of 1.5, a typical value for The Netherlands. It was found that scattering by the boundary layer aerosol contributed on average 80% to the total atmospheric aerosol optical depth. The uncertainty in this value is estimated to be of the order of 13%. Ammonium nitrate dominated the light scattering. This is an anthropogenic aerosol component. The radiative forcing caused by the light scattering of the anthropogenic aerosol was calculated assuming an upward scattered fraction of 0.3. An average value of − 12 W m −2 was found (with an estimated uncertainty of 20%). This corresponds to an absolute increase in the planetary albedo of 0.03, which is equivalent to a 15% increase in the local planetary albedo of 0.2.

A high resolution electrical mobility aerosol spectrometer (MAS)

Abstract A new aerosol sizer with a resolution of 4% has been constructed, which is applicable in the particle size range of 0.01–1 μm. The spectrometer consists of a DMA (Differential Mobility Aerosol Analyzer, TSI 3071) which classifies the particles while the transmitted aerosol is counted by the new very sensitive CCNC (Continuous Condensation Nucleus Counter, TSI 3020). Calibration and the data reduction for the instrument, which is called MAS (Mobility Aerosol Spectrometer), are described in full detail. Application of the spectrometer was found in the characterization of the output of various types of nebulizers. Furthermore, the instrument was used for the size measurement of aerosol which is formed under UV-irradiation in a smog chamber. The size distributions of this aerosol is log-normal having a width ( σ g ) of 1.28 ± 0.02, and this form and width are preserved during coagulation where the median diameter increases from 0.02 to 0.05 μm. The coagulation rate constant averages 21 (±6)· 10 −10 cm 3 /sec. The size distribution obtained using the present instrument was compared with that obtained via the standard EAA (TSI 3030) and the best agreement was found when the SIMPLEX correction code was used. Whereas the aerosol volume as measured via MAS and EAA (irrespective of the correction procedure) agrees well in the size range of 0.05–0.15 μm, discrepancies of an order of magnitude can occur for ambient aerosol where the volume is centered in particles ranging from 0.5 to 1 μm.

Effect of aerosols on the downward shortwave irradiances at the surface: Measurements versus calculations with MODTRAN4.1

[1] A detailed analysis of measurements and model calculations of clear-sky shortwave irradiances at the surface is presented for a set of 18 cases collected during 3 cloudless days in the Netherlands in 2000. The analysis is focused on the influence of the optical and physical properties of aerosols on simulations of direct and diffuse downward solar irradiance at the surface. The properties of aerosols in the boundary layer are derived from surface measurements, under the assumption that all aerosol is confined to a well-mixed atmospheric boundary layer. The simulations of the irradiances are performed with the radiative transfer model MODTRAN 4, version 1.1. The analysis reveals no discernable differences between model and measurement for the direct irradiance, but several significant differences for the diffuse irradiance. The model always overestimates the diffuse irradiance measurements by 7 to 44 Wm � 2 (average: 25 Wm � 2 ). On the basis of an estimated uncertainty in the differences of 18 Wm � 2 , it appears that for 13 out of 18 cases the model significantly overestimates the measurements. This number decreases if instrumental errors (e.g., pyranometer zero-offset) and assumptions on the model input (e.g., wavelength-independent surface albedo) are considered. Nevertheless, the analysis presented here points to a persistent and significant positive model-measurement difference for the diffuse irradiance, which typically amounts to 1–4% of the top-ofatmosphere irradiance, and does not depend on the solar zenith angle. The reason for the discrepancy may be found in the presence of ultrafine absorbing aerosol particles that were not detected by the surface instrument for measuring aerosol absorption. It is also possible that these particles are not present near the surface, due to dry deposition, but do contribute to the total extinction if they are situated higher up in the boundary layer. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation; 1610 Global Change: Atmosphere (0315, 0325); KEYWORDS: aerosol-radiation interaction, shortwave closure

Trends in summer sulphate in Europe

Abstract A trend analysis of the sulphate concentration in Europe in the summer half-year was performed. Data from various measuring networks were analysed, but only stations with quality assured sampling methods and a record of more than 10 years were included in the study. 1978 served as the reference year for the trend, because in that year most stations started operation. The relatively dense network in Belgium provided the most valuable data, as evidenced by the fact that two sites at a distance of only 10 km apart correlated better than 95% over a month. The two sites also show a correlation of better than 90% over a season with two other stations at distances of 45 and 95 km. The relative decrease in summer-sulphate at the four stations in Belgium, as analysed by linear regression, was 3.3% per year which corresponds to an absolute decrease of 0.42 μgm −3 per year. In the Netherlands the average yearly decrease in summer-sulphate at two stations was 3.5% (−0.34 μgm −3 ). In other countries stations were further apart or only a single site wits in use, which limits the representativeness of the data. In northwestern Germany, a region with several monitoring stations, a yearly averaged decrease of 3.0% occurred. The lower absolute decrease (0.25 μgm −3 ) per year compared to that in the two neighbouring countries reflects the lower summer-time sulphate concentrations. In the remainder of Germany the average decrease was 1.6%. In South-Scandinavia the yearly relative decrease at two sites was 2.6% (0.13 μgm −3 absolute). There was no significant trend in the U.K. Al the Polish station the levels increased, it decreased at the Hungarian and Austrian station and remained constant at the Czechoslovakian site. Reasons for omission of the data from France from the trend analysis are discussed.