Gerard Kos

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.

Land use regression model for ultrafine particles in Amsterdam.

There are currently no epidemiological studies on health effects of long-term exposure to ultrafine particles (UFP), largely because data on spatial exposure contrasts for UFP is lacking. The objective of this study was to develop a land use regression (LUR) model for UFP in the city of Amsterdam. Total particle number concentrations (PNC), PM10, PM2.5, and its soot content were measured directly outside 50 homes spread over the city of Amsterdam. Each home was measured during one week. Continuous measurements at a central urban background site were used to adjust the average concentration for temporal variation. Predictor variables (traffic, address density, land use) were obtained using geographic information systems. A model including the product of traffic intensity and the inverse distance to the nearest road squared, address density, and location near the port explained 67% of the variability in measured PNC. LUR models for PM2.5, soot, and coarse particles (PM10, PM2.5) explained 57%, 76%, and 37% of the variability in measured concentrations. Predictions from the PNC model correlated highly with predictions from LUR models for PM2.5, soot, and coarse particles. A LUR model for PNC has been developed, with similar validity as previous models for more commonly measured pollutants.

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.

Contrasts in oxidative potential and other particulate matter characteristics collected near major streets and background locations.

Background: Measuring the oxidative potential of airborne particulate matter (PM) may provide a more health-based exposure measure by integrating various biologically relevant properties of PM into a single predictor of biological activity. Objectives: We aimed to assess the contrast in oxidative potential of PM collected at major urban streets and background locations, the associaton of oxidative potential with other PM characteristics, and the oxidative potential in different PM size fractions. Methods: Measurements of PM with aerodynamic diameter ≤ 10 μm (PM10), PM with aerodynamic diameter ≤ 2.5 μm (PM2.5), soot, elemental composition, and oxidative potential of PM were conducted simultaneously in samples from 8 major streets and 10 urban and suburban background locations in the Netherlands. Six 1-week measurements were performed at each location over a 6-month period in 2008. Oxidative potential was measured as the ability to generate hydroxyl radicals in the presence of hydrogen peroxide in all PM10 samples and a subset of PM2.5 samples. Results: The PM10 oxidative potential of samples from major streets was 3.6 times higher than at urban background locations, exceeding the contrast for PM mass, soot, and all measured chemical PM characteristics. The contrast between major streets and suburban background locations was even higher (factor of 6.5). Oxidative potential was highly correlated with soot, barium, chromium, copper, iron, and manganese. Oxidative potential of PM10 was 4.6 times higher than the oxidative potential of PM2.5 when expressed per volume unit and 3.1 times higher when expressed per mass unit. Conclusions: The oxidative potential of PM near major urban roads was highly elevated compared with urban and suburban background locations, and the contrast was greater than that for any other measured PM characteristic.

Relationship between different size classes of particulate matter and meteorology in three European cities

Evidence on the correlation between particle mass and (ultrafine) particle number concentrations is limited. Winter- and spring-time measurements of urban background air pollution were performed in Amsterdam (The Netherlands), Erfurt (Germany) and Helsinki (Finland), within the framework of the EU funded ULTRA study. Daily average concentrations of ambient particulate matter with a 50% cut off of 2.5 microm (PM2.5), total particle number concentrations and particle number concentrations in different size classes were collected at fixed monitoring sites. The aim of this paper is to assess differences in particle concentrations in several size classes across cities, the correlation between different particle fractions and to assess the differential impact of meteorological factors on their concentrations. The medians of ultrafine particle number concentrations were similar across the three cities (range 15.1 x 10(3)-18.3 x 10(3) counts cm(-3)). Within the ultrafine particle fraction, the sub fraction (10-30 nm) made a higher contribution to particle number concentrations in Erfurt than in Helsinki and Amsterdam. Larger differences across the cities were found for PM2.5(range 11-17 microg m(-3)). PM2.5 and ultrafine particle concentrations were weakly (Amsterdam, Helsinki) to moderately (Erfurt) correlated. The inconsistent correlation for PM2.5 and ultrafine particle concentrations between the three cities was partly explained by the larger impact of more local sources from the city on ultrafine particle concentrations than on PM2.5, suggesting that the upwind or downwind location of the measuring site in regard to potential particle sources has to be considered. Also, relationship with wind direction and meteorological data differed, suggesting that particle number and particle mass are two separate indicators of airborne particulate matter. Both decreased with increasing wind speed, but ultrafine particle number counts consistently decreased with increasing relative humidity, whereas PM2.5 increased with increasing barometric pressure. Within the ultrafine particle mode, nucleation mode (10-30 nm) and Aitken mode (30-100 nm) had distinctly different relationships with accumulation mode particles and weather conditions. Since the composition of these particle fractions also differs, it is of interest to test in future epidemiological studies whether they have different health effects.

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

Abstract 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.

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

Respiratory effects of a reduction in outdoor air pollution concentrations.

Background: Air pollution has been associated with respiratory health effects. There is little direct evidence that reductions in air pollution related to abatement policies lead to actual improvement in respiratory health. We assessed whether a reduction in (traffic policy-related) air pollution concentrations was associated with changes in respiratory health. Methods: Air pollution concentrations and respiratory health were measured in 2008 and 2010 at eight busy urban streets and at four suburban background control locations. Respiratory function was assessed twice in 661 residents by spirometry and measurements of airway resistance. Nitric oxide (NO) in exhaled air was measured as a marker for airway inflammation. Results: Air pollution concentrations were lower in 2010 than in 2008. The declines in pollutants varied among locations, with the largest decline observed in a street with a large reduction in traffic intensity. In regression analyses adjusted for important covariates, reductions in concentrations of soot, NO2, NOx, Cu, and Fe were associated with increases in forced vital capacity (FVC) (∼1% increase per interquartile range [IQR] decline). Airway resistance decreased with a decline in particulate matter (PM10) and PM2.5 (9% per IQR), although these associations were somewhat less consistent. No associations were found with exhaled NO. Results were driven largely by one street where traffic-related air pollution showed the largest reduction. Forced expiratory volume and FVC improved by 3% to 6% in residents of this street compared with suburban background residents. This was accompanied by a suggestive reduction in airway resistance. Conclusions: Reductions in air pollution may lead to small improvements in respiratory function.

A High-Flow Turbulent Cloud Chamber

ABSTRACT A large laboratory facility (cloud chamber) has been built to study cloud formation under reproducible conditions. The chamber was designed to assess the influence of anthropogenic aerosols on the microstructure of marine clouds in coastal Western Europe. For this reason the supersaturations in the chamber are low, in the order of 0.1%, typical for coastal marine stratus. The very large size (30 m3) and flow (30 m3/min) of the chamber allow unperturbed use of conventional cloud instrumentation like Forward Scattering Spectrometer Probe (TSI Inc.) and high-flow cascade impactors for chemical analysis of aerosol and droplets. The performance of the cloud chamber was tested with laboratory-generated submicron-sized ammonium sulphate aerosol with a lognormal size distribution and varying the number concentrations. It was found that the sulphate particles above a threshold size of 0.07 or 0.1 μm in diameter (dependent on the settings) grew into droplets (became “activated”), which corresponds accordin...

Collocated observations of cloud condensation nuclei, particle size distributions, and chemical composition

Cloud condensation nuclei (CCN) number concentrations alongside with submicrometer particle number size distributions and particle chemical composition have been measured at atmospheric observatories of the Aerosols, Clouds, and Trace gases Research InfraStructure (ACTRIS) as well as other international sites over multiple years. Here, harmonized data records from 11 observatories are summarized, spanning 98,677 instrument hours for CCN data, 157,880 for particle number size distributions, and 70,817 for chemical composition data. The observatories represent nine different environments, e.g., Arctic, Atlantic, Pacific and Mediterranean maritime, boreal forest, or high alpine atmospheric conditions. This is a unique collection of aerosol particle properties most relevant for studying aerosol-cloud interactions which constitute the largest uncertainty in anthropogenic radiative forcing of the climate. The dataset is appropriate for comprehensive aerosol characterization (e.g., closure studies of CCN), model-measurement intercomparison and satellite retrieval method evaluation, among others. Data have been acquired and processed following international recommendations for quality assurance and have undergone multiple stages of quality assessment.