Figure - available from: Environmental Monitoring and Assessment
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Air quality map of the study area in Antwerp (3.5 by 5 km), modeled NO2 concentrations for 2015 (adapted from Vranckx and Lefebvre 2013). The locations of the saplings are marked with circles, the locations of the adult trees are marked with squares
Source publication
This study examines the role of dorsiventral leaf measurements in reflectance-based air quality estimation. The dorsiventral asymmetry is used to describe the difference between the upper (adaxial) and lower (abaxial) leaf side. Spectral characteristics of dorsiventral asymmetry and both adaxial and abaxial leaf reflectance are investigated for a t...
Citations
... Tilia sp., Corylus sp., Ulmus sp.) the adaxial leaf lamina is rotated and the majority mature leaves simultaneously face the adaxial side upward (Charlton, 1993). The mesophyll cells and intercellular spaces distribution asymmetry and different structure of adaxial and abaxial epidermis strongly affect leaf reflectance not only in dorsiventral (Brackx et al., 2017;Brakke et al., 1993; but also in equifacial (Vergara-Díaz et al., 2018) leaves. In contrast to reflectance, transmittance is independent on the leaf side illuminated (Brakke et al., 1993;Demarez, 1999). ...
... Environmental factors (particularly water scarcity) can also modulate the difference between adaxial and abaxial reflectance as shown for equifacial flag leaves of durum wheat (Vergara-Díaz et al., 2018) where water stress diminished leaf side-related reflectance differences. Dorsiventral leaf optical properties may be a useful tool in assessment tree physiological status as shown for pollution monitoring in urban sites detected by remote sensing methods (Brackx et al., 2017;Zadeh et al., 2012). ...
... In the next step, we focused on linking leaf structural traits related to tissue thickness and the leaf optical properties. Previous studies suggest a relationship between the reflectance and transmittance partitioning in NIR wavelengths and total leaf thickness (Knapp and Carter, 1998), while the thickness of palisade and spongy mesophyll parenchyma was hypothesized to drive the dorsiventral leaf reflectance asymmetry in visible region (Baránková et al., 2016;Brackx et al., 2017). This was theoretically confirmed by the sensitivity analysis of the DLM model. ...
This study analyzed spectral variations of the particulate matter (PM hereafter)-exposed pine trees using a spectrometer and a hyperspectral imager to derive the most effective spectral indices to detect the pine needle exposure to PM emission. We found that the spectral variation in the near-infrared (NIR hereafter) bands systemically coincided with the variations in PM concentration, showing larger variations for the diesel group whereas larger dust particles showed spectral variations in both visible and NIR bands. It is because the PM adsorption on needles is the main source of NIR band variation, and the combination of visible and NIR spectra can detect PM absorption. Fourteen bands were selected to classify PM-exposed pine trees with an accuracy of 82% and a kappa coefficient of 0.61. Given that this index employed both visible and NIR bands, it would be able to detect PM adsorption. The findings can be transferred to real-world applications for monitoring air pollution in an urban area.
