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Although Humic-LIke Substances (HULIS) are important contributors to the mass of organic aerosol in airborne particulate matter (PM), little is known about their chemical composition, while, their size-resolved optical properties have not been studied yet. Here, HULIS fractions were isolated from size-resolved aerosol samples (≤0.49, 0.49–0.95, 0.95–3 and 3–10 μm) collected in urban and suburban environments of four European cities during wintertime. The bulk (i.e., sum of all size fractions) concentration of HULIS ranged between 1.29 and 2.80 μg m−3 across sites with highest values in the ≤0.49 μm particle size fraction. The contribution of the carbon mass of HULIS (HULIS-C) to the water-soluble organic carbon content (WSOC) of PM was 32–43%, which is typical for urban sites affected by biomass burning. The Mass Absorption Efficiency (MAE), which characterizes the efficiency of absorbing solar energy per carbon mass of HULIS decreased with particle size, suggesting that the finest size fractions contain more light-absorbing chromophores, which could affect the light-absorbing ability of organic aerosols. The good correlation of HULIS with effective biomass tracers such as K+, as well as with secondary inorganic aerosol components, proposed that HULIS had both primary (i.e., biomass burning) and secondary sources. The Fourier Transfer Infrared coupled to Attenuation Total Reflectance (FTIR-ATR) spectra demonstrated prevalence of aromatic over carboxylic functional groups in most HULIS fractions, indicating contribution from coal combustion emissions in addition to fresh biomass burning aerosol. The new findings add to better understanding the sources and chemical structure of HULIS in urban and suburban environments.

Degradation of semivolatile organic compounds (SVOCs) occurs naturally in ambient air due to reactions with reactive trace gases (e.g., ozone, NOx). During air sampling there is also the possibility for degradation of SVOCs within the air sampler, leading to underestimates of ambient air concentrations. We investigated the possibility of this sampling artifact in commonly used active and passive air samplers for seven classes of SVOCs, including persistent organic pollutants (POPs) typically covered by air monitoring programs, as well as SVOCs of emerging concern. Two active air samplers were used, one equipped with an ozone denuder and one without, to compare relative differences in mass of collected compounds. Two sets of passive samplers were also deployed to determine the influence of degradation during longer deployment times in passive sampling. In active air samplers, comparison of the two sampling configurations suggested degradation of particle-bound polycyclic aromatic hydrocarbons (PAHs), with concentrations up to 2× higher in the denuder-equipped sampler, while halogenated POPs did not have clear evidence of degradation. In contrast, more polar, reactive compounds (e.g., organophosphate esters and current use pesticides) had evidence of losses in the sampler with denuder. This may be caused by the denuder itself, suggesting sampling bias for these compounds can be created when typical air sampling apparatuses are adapted to limit degradation. Passive air samplers recorded up to 4× higher concentrations when deployed for shorter consecutive sampling periods, suggesting that within-sampler degradation may also be relevant in passive air monitoring programs.

Polyurethane foam (PUF) passive air samplers (PAS) are widely used for measurements of persistent organic pollutants (POPs) and other semi-volatile organic compounds (SVOCs) in large-scale monitoring networks as well as in case studies around the globe. Calibration of PUF-PAS is performed by field-based calibration studies or passive sampler uptake models, but both these are typically performed and/or validated in temperate zones, while the sampling rates are more widely applied, including in tropical and polar zones. Here, we present field-based calibrations results for MONET PUF-PAS from a subtropical and tropical site (Nairobi, Kenya and Accra, Ghana) based on side-by-side deployment of PUF-PAS and active air samplers (AAS), as well as model PAS uptake from available passive sampler uptake models. By comparing these results with a similar calibration from a temperate site (Brno, Czech Republic), we show that the higher ambient temperatures result in higher effective sampling rates for intermediate molecular weight SVOCs (logKOA of 7–11) as a result of lower particle-bound fraction, and in lower sample volumes for lighter SVOCs (logKOA

The central and eastern Mediterranean is a receptor area for persistent organic pollutants (POPs) emitted in western, central and eastern Europe, particularly during summer. Atmospheric concentrations of PCBs, DDXs, PBDEs, penta- and hexachlorobenzene were measured during a ship-borne survey in the summer of 2010. The concentration of PCBs (sum of 7 congeners) was 3.61 (2.08-7.72) pg m(-3), of which 6.7% was associated with the particulate phase. The mean concentration of DDT isoi-ners and their metabolites, DDE and DDD, was 2.60 (0.46-7.60) pg m(-3) (particulate mass fraction theta = 0.097), of penta- and hexachlorobenzene 0.22 (