Gaseous polycyclic aromatic hydrocarbon concentrations are higher in urban forests than adjacent open areas during summer but not in winter – Exploratory study

Abstract

While the potential of plants to uptake polycyclic aromatic hydrocarbons (PAHs) is widely acknowledged, empirical evidence of the effects of this process on local atmospheric PAH concentrations and human health is tenuous. We measured gaseous PAH concentrations using passive samplers in urban tree-covered areas and adjacent open, treeless areas in a near-road environment in Finland to gain information on the ability of urban vegetation to improve air quality. The ability of urban, mostly deciduous, vegetation to affect PAHs was season dependent: during summer, concentrations were significantly higher in tree-covered areas, while in the fall, concentrations in open areas exceeded those in tree-covered areas. During winter, concentrations in tree-covered areas were either lower or did not differ from those in open areas. Results of this study imply that the commonly believed notion that trees unequivocally improve air quality does not apply to PAHs studied here.

Urban forests near roads do not reduce gaseous air pollutant concentrations but have an impact on particles levels

“…The current study conducted in Helsinki corroborates results from other studies in Nordic urban environments (Setälä et al, 2013;Viippola et al, 2016); the impact of the tree canopy, at least in near-road environments without buildings, is negligible regarding the concentrations of certain gaseous air pollutants. Alternatively, it may be that these gaseous pollutants were absorbed to some extent by the canopy, but not sufficiently so to compensate for increased concentrations due to reduced air-flow in tree-covered areas (see Janhäll, 2015).…”

Greenbelts do not reduce NO2 concentrations in near-road environments

“…Since the tree canopy can reduce flow, dilution and mixing of polluted air (Belcher et al, 2012;Gromke & Ruck, 2009;Renaud et al, 2011;Wuyts et al, 2008), these effects can increase pollutant levels inside the canopy, as reported by, e.g. Harris & Manning (2010), Setälä et al (2013), Viippola et al (2016) and Vos et al (2013). In the absence of greenbelts or other tree cover, polluted air mass dilutes more rapidly by higher wind velocity, which brings about lower pollutant concentrations in open areas.…”

“…For example, vegetation can reduce wind speed not only during the leaf period (Setälä et al, 2013) but also during the leafless period, as has been shown by Renaud et al (2011) in deciduous forests in Switzerland. Although such reduced ventilation can increase pollutant levels within green infrastructures during summer (Viippola et al, 2016), no one has, to our knowledge, documented this to take place during leafless periods in winter. The increase in NO 2 levels inside the greenbelts with (i) the number of large trees and (ii) the proportion of broadleaf trees also in winter, further suggests that large canopy structures, also without leaves, can reduce air movement under them leading to higher NO 2 levels.…”

“…in a forest or park and compared to concentrations in adjacent open, treeless areas, have been scarce. However, an increasing number of such studies, especially those performed in near-road environments, have been published (Brantley et al, 2014;Fantozzi et al, 2015;Harris & Manning, 2010;Setälä et al, 2013;Tong et al, 2015;Viippola et al, 2016;Yin et al, 2011;Yli-Pelkonen et al, 2017). For example and Yli-Pelkonen et al (2017) observed no significant differences in gaseous pollutant concentrations between tree-covered urban parks or remnant forests and open areas in near-road environments in hemi-boreal climatic conditions, while Viippola et al (2016) found higher PAH concentrations under tree canopies than in nearby open areas close to roads in Finland.…”

Arborização urbana e qualidade do ar na cidade de São Paulo

“…Já 27% dos estudos, utilizaram análises de uso e ocupação do solo, através de sensoriamento remoto, imagens de satélite de alta resolução, softwares como ArcGis e Landsat (ALONSO et al, 2011;ANDRUSAITYTE et al, 2016;BEYER et al, 2014;CHAN et al, 2015;CHEN et al, 2016;CURRIE;BASS, 2008;GARCÍA-GÓMEZ et al, 2016;GRAZULEVICIENE et al, 2015;HYSTAD et al, 2014;KABISCH;HAASE;VAN DEN BOSCH, 2016;KARDAN et al, 2015;KIHAL-TALANTIKITE et al, 2013;MANES et al, 2012;MORANI et al, 2011;QIU et al, 2009;TSAO et al, 2014;WU et al, 2015b QIU et al, 2009;SALMOND et al, 2013;SHANDAS et al, 2016;VIIPPOLA et al, 2016;WANG et al, 2012).…”