Dispersion of Volatile Hydrocarbons in Urban Street Canyons

Abstract

Volatile hydrocarbons (VHCs) were monitored in two urban street canyons for 16 days. Measurements of 15 selected VHCs were performed simultaneously at three different sampling heights: at street level (2 m), at 8 m, and at the rooftop (25 m above the ground). The aim of the study was to investigate the factors responsible for the horizontal and vertical changes in VHC concentrations. Physical parameters controlling the concentration gradients (wind flow and speed) were enabled. It was concluded that dilution and dispersion decrease the concentrations of HCs emitted at street level by approximately a factor of 6 between rooftop and street levels. Low winds and winds parallel to the street axis were identified as the worst dispersion conditions. The correlation between the measured VHC concentrations gave an insight into their fate. An empirical relationship between CO and benzene was established. These results may have important implications in planning monitoring studies to support research on population exposure in urban areas.

Estimating airborne pollutant concentrations in vegetated urban sites using statistical models with microclimate and urban geometry parameters as predictor variables: A case study in the city of Athens Greece

“…[29] In a recent and more detailed study for urban streets, it was found that dilution and dispersion decrease the pollutant concentrations emitted at street level by approximately a factor of 6 between rooftop and street levels while low wind speeds were identified as the worst dispersion conditions. [21] Similarly, for urban parks, an early study showed that the plant density and structure provide an intensive decline in pollutant levels in the central area of the parks. [30] In another study, it was found that pollutant levels are greater at the peripheral than the central zones of the parks.…”

“…typical streets in Jerusalem have an aspect ratio of 0.5, [20] while aspect ratios for typical Athens streets may range from 1.2 to 4.2. [21] The selected sites are representatives of the Athens urban microenvironment; they have a variety of urban topography-geometry configurations and include parks, public squares with and without green areas and 'canyon' streets with trees. Measurements carried out and samples were collected from totally 28 different locations: 5 locations in two different parks, 14 locations in street canyons, and 9 locations in public squares (3 with areas of 1.0 ha, 3 with areas of 5.0 ha and 3 with areas of 10.0 ha).…”

The role of primary and secondary air pollutants in atmospheric pollution: Athens urban area as a case study

“…Extensive research has been launched in recent years to study the pollutants dispersion in street canyons and recently a study has been published for VOCs dispersion in an Athens street canyon (Bakeas and Siskos 2003). In this study, inter-correlations of VOCs (r 2 ) were found to change with height of the sampling point in the street canyons.…”

“…3 Percentages of estimated photochemical production of carbonyls during a summer-day (a) and a winter-day (b). Source: Bakeas et al 2003Environ Chem Lett (2008 orders of magnitude from those of acetaldehyde and three orders of magnitude from those of ozone.…”

“…4 Calculated formation rates of OH radical from photolysis of formaldehyde, during a typical warm (a) and cold day (b). Source: Bakeas et al 2003 because of their widespread occurrence in the environment (Frank et al 1995). With respect to ecotoxicological considerations, chloroacetic acids (CAAs) are important because of their phytotoxicity as TCA and DCA have been used as herbicides until the late 1980s, and several anilides of MCA are still in use such as Alachlor and Metolachlor.…”