Inhalation bioaccessibility of polycyclic aromatic hydrocarbons in heavy PM2.5 pollution days: Implications for public health risk assessment in northern China.

Airborne (PM2.5) with aerodynamic diameter ≤ 2.5 µm was collected from 4 types of cities in northeast China during the heating period. The objectives of this study were to assess the concentrations variation of PM2.5-bound 12 carcinogenic polycyclic aromatic hydrocarbons (PAH12), to study the influence of simulated lung fluids on bioaccessibility of PAH12 and to estimate the variation of lifetime excess cancer risk to the residents, artificial lysosomal fluid (ALF) and Gamble's solution were used. The number of lifetime excess cancer cases (determined by California Environmental Protection Agency method) as a result of PAH12 exposure (total concentration) was 4.00-430 (provincial central cities), 24.0-261 (energy-mining cities), 17.0-109 (forested city), and 20.0-69.0 (agricultural city) per million people, which relatively corresponded to a 92.2% and 96.2%, 92.6% and 97.3%, 92.2% and 94.2%, and 86.5% and 92.6% decrease after considering bioaccessibility following 24-h of Gamble's solution and ALF extraction, respectively. Phenanthrene (Phe), dibenz[a,h]anthracene (DahA) and benzo[a]pyrene (BaP) were found to be the most bioaccessible types of PAH12 after the Gamble's solution and ALF extraction in the PM2.5 samples from all the studied cities. Based on the point-estimate approach, short-term predictions of pulmonary toxicity caused by potential inhalation of airborne PM into the pulmonary system might be overestimated if bioaccessibility of PM2.5-bound PAH12 is not fully evaluated.

The impact of urban open space and 'lift-up' building design on building intake fraction and daily pollutant exposure in idealized urban models.

Sustainable urban design is an effective way to improve urban ventilation and reduce vehicular pollutant exposure to urban residents. This paper investigated the impacts of urban open space and 'lift-up' building design on vehicular CO (carbon monoxide) exposure in typical three-dimensional (3D) urban canopy layer (UCL) models under neutral atmospheric conditions. The building intake fraction (IF) represents the fraction of total vehicular pollutant emissions inhaled by residents when they stay at home. The building daily CO exposure (Et) means the extent of human beings' contact with CO within one day indoor at home. Computational fluid dynamics (CFD) simulations integrating with these two concepts were performed to solve turbulent flow and assess vehicular CO exposure to urban residents. CFD technique with the standard k-ε model was successfully validated by wind tunnel data. The initial numerical UCL model consists of 5-row and 5-column (5×5) cubic buildings (building height H=street width W=30m) with four approaching wind directions (θ=0°, 15°, 30°, 45°). In Group I, one of the 25 building models is removed to attain urban open space settings. In Group II, the first floor (Lift-up1), or second floor (Lift-up2), or third floor (Lift-up3) of all buildings is elevated respectively to create wind pathways through buildings. Compared to the initial case, urban open space can slightly or significantly reduce pollutant exposure for urban residents. As θ=30° and 45°, open space settings are more effective to reduce pollutant exposure than θ=0° and 15°.The pollutant dilution near or surrounding open space and in its adjacent downstream regions is usually enhanced. Lift-up1 and Lift-up2 experience much greater pollutant exposure reduction in all wind directions than Lift-up3 and open space. Although further investigations are still required to provide practical guidelines, this study is one of the first attempts for reducing urban pollutant exposure by improving urban design.