Greenbelts do not reduce NO2 concentrations in near-road environments

Abstract

Trees are believed to improve air quality, thus providing an important ecosystem service for urban inhabitants. However, empirical evidence on the beneficial effects of urban vegetation on air quality at the local level and in boreal climatic regions is scarce. We studied the influence of greenbelt-type forest patches on NO 2 levels (i) in front of, (ii) inside and (iii) behind greenbelts next to major roads in the Helsinki Metropolitan Area, Finland, during summer and winter using passive collectors. Concentrations of NO 2 were significantly higher in front of greenbelts compared to road sides without greenbelts. The more trees there were inside greenbelts the higher the NO 2 level in front of greenbelts, likely due to the formation of a recirculation zone of air flow in front of greenbelts. Similarly, NO 2 levels were higher inside greenbelts than in open areas without them, likely due to reduced air flow inside greenbelts. NO 2 levels behind greenbelts were similar to those detected at the same distance from the road but without greenbelts. Our results suggest that, regardless of season, roadside greenbelts of mostly broadleaf trees do not reduce NO 2 levels in near-road environments, but can result in higher NO 2 levels in front of and inside greenbelts.  NO 2 levels were higher in front of and inside greenbelts than in nearby open areas  NO 2 levels were not lower behind greenbelts than in open areas without greenbelts  Denser greenbelts increased NO 2 concentrations between roads and greenbelts  Reduced air flow in front of and inside greenbelts resulted in higher NO 2 levels  NO 2 levels behind greenbelts did not decrease due to a greenbelt-induced windbreak

Field investigations for evaluating green infrastructure effects on air quality in open-road conditions

“…These concentrations could be due to a relatively low height of HCB (<1m) that is insufficient to create a barrier effect. Similarly, past investigations have reported mixed results of pollutant concentrations behind trees that emerged from a lack of barrier effect at breathing height and lower density (Brantley et al, 2014;Chen et al, 2016;Hagler et al, 2012;Viippola et al, 2018;Yli-Pelkonen et al, 2017). In addition, major reasons for higher pollutant concentrations behind trees (TCB; single tree row) compared with TIB (multiple tree rows, up to 4) was due to the difference in thickness of tree rows and lower canopy to ground distance.…”

“…The literature reports varying level of differences in pollutant concentration depending on the GI type (Abhijith et al, 2017;Chen et al, 2015;Hagler et al, 2012). For example, some studies showed decreased concentrations due to hedges (Tiwary et al 2008;Al-Dabbous and Kumar, 2014) whereas others showed that trees can result in both air quality deterioration (Tong et al, 2015;Morakinyo et al, 2016;Yli-Pelkonen et al, 2017 ) and improvement (Yin et al, 2011;Lin et al, 2016). Before drawing generalisations on the air quality benefits of GI, it is important to consider the type of pollutants evaluated and reflected in any associated guidelines.…”

Pembangunan Green Belt Sebagai Antisipasi Pencemaran Udara Industri Pupuk Di Kalimantan Timur

“…Dengan pilihan pilihan tanaman yang tepat dan luasan areal tertentu akan mampu menurunkan polusi suatu industri (1,12,13) . Beberapa kajian dengan lebar green belt mencapai 500 meter, Green belt mampu menurunkan polusi udara suatu kawasan (24,25) , sebaliknya dengan lebar green belt yang terbatas, seperti ditepian jalan raya, upaya tersebut tidak maksimal menurunkan kandungan pencemaran udara ambien (26,27,28) .…”

“…Dengan alasan tersebut, ada suatu kehawatiran, rencana pembangunan Green Belt dengan lebar 50 dan panjang 600 meter di rencana kawasan industri KIE (5) , tidak menghasilkan penurunan polusi udara yang signifikan (26,27,28) . Hanya saja, untuk rencana kawasan industri pupuk KIE, selain kualitas udara ambien eksisiting yang masih baik (4,5) , hasil simulasi model konsentrasi gas buang dari cerobong rencana industri pupuk KIE telah memenuhi ketentuan baku mutu (6) .…”

“…Komposisi tanaman yang diusulkan untuk menyusun tanaman green belt telah dipilih sesuai kebutuhan (26,27,28) .…”