Vertical concentration gradients of volatile organic compounds in two NS-oriented street canyons

BTEX and PAH contributions to Lake Kinneret water: a seasonal-based study of volatile and semi-volatile anthropogenic pollutants in freshwater sources

Benzene , toluene, ethylbenzene, and xylenes (BTEX) BTEX molecules are toxic components, ubiquitous in the environment, often found in concentrations- a few orders of magnitude higher than the well-studied PAHs levels. This fact is demonstrated in either crude oil, fuels, water, and air samples. BTEX studies focus mainly on the airborne levels of these molecules, while their waterborne presence is understudied. In this study, BTEX levels were assessed at Lake Kinneret, Israel. As a result, 0-1.5 ppb of BTEX was recorded in five stations (2021-2022). Elevated BTEX levels (3-10 ppb) were recorded at the northern rivers nourishing this lake, implying the existence of remote polluting sources. Transect air samplings of BTEX conducted at the lake next to the bathing season of 2021 revealed airborne BTEX levels between 0.8 and 10 µg/m³, peaking up close to the bathing season, yet inconsistent with the BTEX water level trend. Lake water samples collected next to Tiberias city outfalls following the "Carmel" rainstorm showed elevated concentrations of BTEX up to 35 ppb and PAHs up to 0.47 ppb with an urban isotopic signal. The remote station's PAHs levels were less than one order of magnitude, with a distinct rural isotopic signal. Additionally, a human-specific microbial marker revealed increased sewer contributions at some of the urbansites. The results of this study show that a wide area dispersion of low atmospheric BTEX levels exists in the lake's perimeter. The dispersion rate is most likely influenced by season-based factors, e.g., motors and biomass fires. The unstudied waterborne BTEX levels in this lake are influenced by rivers, city runoff, and other yet unknown factors that may contribute to the sedimentation of these components. This process may result in a chronic pollution state. Despite the BTEX's medium-low solubility and high volatility, its under-evaluated waterborne transportation may lead to high toxic levels following bioaccumulation.

Assessing outdoor air quality vertically in an urban street canyon and its response to microclimatic factors

The vertical distribution of air pollutants in urban street canyons is closely related to residents' health. However, the vertical air quality in urban street canyons has rarely been assessed using field observations obtained throughout the year. Therefore, this study investigated the seasonal and annual concentrations of particulate matter (PM_2.5 and PM₁₀), CO, NO₂, SO₂, O₃, air quality index, and their responses to microclimatic factors at three height levels (1.5, 27, and 69 m above street level) in an urban street canyon. The PM concentration was higher at 27 m than at 1.5 m in winter, whereas the situation was reversed in other seasons. It was found that photochemical pollutants such as NO₂ and O₃ were the primary pollutants in the urban street canyon. The days on which O₃ was the primary pollutant at the height of 1.5 m accounted for 81.07% of the entire year. The days on which NO₂ was the primary pollutant at the height of 27 and 69 m accounted for 82.49% and 72.33% of the entire year, respectively. Substantially higher concentrations of NO₂ and O₃ were found at the height of 27 m than at 69 m. In-canyon concentrations of NO₂ and O₃ were strongly correlated with air temperature, wind speed, and wind direction, which played important roles in photochemical reactions and pollutant dispersion.