The Representativeness of Outdoor Particulate Matter Concentrations for Estimating Personal Dose and Health Risk Assessment of School Children in Lisbon

This study investigated the suitability of outdoor particulate matter data obtained from a fixed monitoring station in estimating the personal deposited dose. Outdoor data were retrieved from a station located within the urban area of Lisbon and simulations were performed involving school children. Two scenarios were applied: one where only outdoor data were used assuming an outdoor exposure scenario, and a second one where an actual exposure scenario was adopted using the actual microenvironment during typical school days. Personal PM₁₀ and PM_2.5 dose (actual exposure scenario) was 23.4% and 20.2% higher than the ambient (outdoor exposure scenario) PM₁₀ and PM_2.5 doses, respectively. The incorporation of the hygroscopic growth in the calculations increased the ambient dose of PM₁₀ and PM_2.5 by 8.8% and 21.7%, respectively. Regression analysis between the ambient and personal dose showed no linearity with R² at 0.07 for PM₁₀ and 0.22 for PM_2.5. On the other hand, linear regression between the ambient and school indoor dose showed no linearity (R² = 0.01) for PM₁₀ but moderate (R² = 0.48) for PM_2.5. These results demonstrate that ambient data must be used with caution for the representativeness of a realistic personal dose of PM_2.5 while for PM₁₀ the ambient data cannot be used as a surrogate of a realistic personal dose of school children.

Missed Evaporation from Atmospherically Relevant Inorganic Mixtures Confounds Experimental Aerosol Studies

Sea salt aerosol particles are highly abundant in the atmosphere and play important roles in the global radiative balance. After influence from continental air, they are typically composed of Na⁺, Cl^-, NH₄⁺, and SO₄^2- and organics. Analogous particle systems are often studied in laboratory settings by atomizing and drying particles from a solution. Here, we present evidence that such laboratory studies may be consistently biased in that they neglect losses of solutes to the gas phase. We present experimental evidence from a hygroscopic tandem differential mobility analyzer and an aerosol mass spectrometer, further supported by thermodynamic modeling. We show that, at normally prevailing laboratory aerosol mass concentrations, for mixtures of NaCl and (NH₄)₂SO₄, a significant portion of the Cl^- and NH₄⁺ ions are lost to the gas phase, in some cases, leaving mainly Na₂SO₄ in the dry particles. Not considering losses of solutes to the gas phase during experimental studies will likely result in misinterpretation of the data. One example of such data is that from particle water uptake experiments. This may bias the explanatory models constructed from the data and introduce errors inte predictions made by air quality or climate models.

Quantifying the influence of urban biotic and abiotic environmental factors on great tit nestling physiology

There is a long history of avian studies investigating the impacts of urbanization. While differences in several life-history traits have been documented, either between urban and rural populations or across generalized urbanization gradients, a detailed understanding of which specific environmental variables cause these phenotypic differences is still lacking. Here, we quantified several local environmental variables coupled to urbanization (air pollution, tree composition, ambient temperature, and artificial light at night [ALAN]) within territories of breeding great tits (Parus major). We linked the environmental variables to physiological measures of the nestlings (circulating fatty acid composition [FA], antioxidant capacity and an oxidative damage marker [malondialdehyde; MDA]), to garner a mechanistic understanding of the impact of urbanization. We found that the antioxidant capacity of nestlings decreased with higher numbers of oak trees and levels of PM_2.5 (airborne particulate matter with a diameter < 2.5 μm). Furthermore, the ratio of ω6:ω3 polyunsaturated FAs, important for immune function, was positively correlated with PM_2.5 concentration, while being negatively associated with ambient temperature and number of non-native trees in the territory. Body mass and wing length both increased with the number of local oak trees. We also show, through a principal component analysis, that while the environmental variables fall into an urbanization gradient, this gradient is insufficient to explain the observed physiological responses. Therefore, accounting for individual environmental variables in parallel, and thus allowing for interactions between these, is crucial to fully understand the urban ecosystem.

Investigation of hygroscopic growth effect on aerosol scattering coefficient at a rural site in the southern North China Plain

Aerosol optical properties and the effect of hygroscopic growth on the scattering coefficients at a rural site in the southern North China Plain were investigated based on a two-month observation conducted in the summer of 2014. The scattering coefficient of dry aerosols was high, with a mean (±standard deviation) of 338.8±209.9Mm^-1 (520nm) during the observation period. A noticeable enhancement in aerosol scattering due to hygroscopic growth was observed, e.g., by a factor of 2.28±0.69 at RH of 80% (referred to as f(RH=80%)) and 3.39±1.14 at RH of 85% (f(RH=85%)). The high content of water-soluble secondary inorganic aerosols (SIAs), accounting for 53.1% of fine particulate matter (i.e., PM_2.5) on average, was mainly responsible for the high hygroscopicity. f(RH=80%) increased with increasing SIA mass fraction in PM_2.5. This was especially the case when SIAs were mainly in finer particulate matter, i.e., PM₁. A number of considerably low f(RH=80%) values was observed due to relatively low mass fraction of SIAs in PM₁ despite high fraction in PM_2.5. Particle size distributions, especially those of SIAs, also played a remarkable role in the hygroscopicity of ambient aerosols. No significant difference in hygroscopicity was found between different pollution episodes due to the dominance of SIAs in all the cases. Slightly higher hygroscopic growth factors were observed during the clean episode, which were attributed to the smaller particle sizes.

Physical properties and lung deposition of particles emitted from five major indoor sources

The physical properties of indoor particles were measured with an Scanning Mobility Particle Sizer (SMPS) system (14.6-850 nm), an Aerodynamic Particle Sizer (APS, 0.54-18 μm) and an Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) in an apartment located in an urban background site in Prague (Czech Republic) from 15 August to 8 September, 2014. The total particle maximum number concentration was 9.38 × 10⁴, 1.46 × 10⁵, 2.89 × 10⁴, 2.25 × 10⁵ and 1.57 × 10⁶ particles cm^-3 for particles released from vacuum cleaning, soap/W5 cleaning spray, smoking, incense burning and cooking (frying) activities, respectively. Particles emitted from cleaning activities showed unimodal number size distributions, with the majority of particles (>98.2 %) in the ultrafine size range (Dp <100 nm) and modes at a diameter of 19.8 nm for vacuum cleaning and 30.6 nm for soap/W5 cleaning. Smoking and incense burning predominantly generated particles in the accumulation mode with a count median diameter around 90-150 nm while cooking emissions showed a bimodal structure with a main mode at 47.8 nm. Particles from vacuum cleaning, incense burning, smoking and cooking emissions were found to be "nearly hydrophobic" with an average growth factor (G_f) around 1.01-1.10, while particles emitted from desk cleaning using organic compounds were found to be "less-hygroscopic" (G_f ∼1.12-1.16). Based on an adjusted MPPD model with a consideration of the hygroscopic properties of particles, the total lung deposition fractions of these particles by number when they penetrate into the human lung were 0.73 ± 0.02, 0.62 ± 0.03, 0.37 ± 0.03, 0.32 ± 0.03 and 0.49 ± 0.02 for vacuum cleaning, desk cleaning, smoking, incense burning and cooking, respectively.