Agrivoltaic systems, comprising photovoltaic panels placed over agricultural crops, have recently gained increasing attention. Emerging interest in these systems led us to investigate their influence on rice crops. Various factors affecting rice crop yield, including fertilizer application, temperature, and solar radiation, were directly observed, and measured to evaluate changes associated with the shading rates of photovoltaic systems installed above rice crops. The results suggest that the allowable upper limit of the shading rate for agrivoltaic installations ranges from 27 to 39%, which sustains at least 80% of the rice yield, a condition set by the Japanese Ministry of Agriculture, Forestry and Fisheries for these systems. If such systems are applied to rice paddies in Japan at 28% density, they could generate 284 million MWh/yr. This is equivalent to approximately 29% of the total Japanese electricity demand, based on 2018 calculations. This projection indicates the potential of agrivoltaic systems for efficient land use and sustainable energy generation.

We conducted simultaneous measurements of concentrations and above-canopy fluxes of isoprene and α-pinene, along with their oxidation products in aerosols in a Larix kaempferi (Japanese larch) forest in summer 2012. Vertical profiles of isoprene showed the maximum concentration near the forest floor with a peak around noon, whereas oxidation products of isoprene, i.e., methacrolein (MACR) and methyl vinyl ketone (MVK), showed higher concentrations near the canopy level of the forest. The vertical profile suggests large emissions of isoprene near the forest floor, likely due to Dryopteris crassirhizoma (a fern species), and the subsequent reaction within the canopy. The concentrations of α-pinene also showed highest values near the forest floor, with maximums in the early morning and late afternoon. The vertical profiles of α-pinene suggest its large emissions from soil and litter in addition to emissions from L. kaempferi leaves at the forest site. Isoprene and its oxidation products in aerosols exhibited similar diurnal variations within the forest canopy, providing evidence of secondary organic aerosol (SOA) formation via oxidation of isoprene most likely emitted from the forest floor. Although high abundance of α-pinene was observed in the morning, its oxidation products in aerosols showed peaks in daytime, due to a time lag between the emission and atmospheric reactions of α-pinene to form SOA. Positive matrix factorization (PMF) analysis indicated that anthropogenic influence is the most important factor contributing to the elevated concentrations of molecular oxidation products of isoprene- (> 64 %) and α-pinene-derived SOA (> 57 %). The combination of the measured fluxes and vertical profiles of biogenic volatile organic compounds (BVOCs) suggests that the inflow of anthropogenic precursors/aerosols likely enhanced the formation of both isoprene SOA and α-pinene SOA within the forest canopy even when the BVOC flux was relatively low. This study highlights the importance of intra-canopy processes that promote biogenic SOA formation in the presence of significant inflow of oxidants together with anthropogenic aerosols and their precursors.

This study presents a methodology for developing a high-resolution (2 m) urban tree canopy leaf area inventory in different tree phenological seasons and a subsequent application of the methodology to a 625 km² urban area in Tokyo. Satellite remote sensing has the advantage of imaging large areas simultaneously. However, mapping the tree canopy cover and leaf area accurately is still difficult in a highly heterogeneous urban landscape. The WorldView-2/3 satellite imagery at the individual tree level (2 m resolution) was used to map urban trees based on a simple pixel-based classification method. The comparison of our mapping results with the tree canopy cover derived from aerial photography shows that the error margin is within an acceptable range of 5.5% at the 3.0 km² small district level, 5.0% at the 60.9 km² municipality level, and 1.2% at the 625 km² city level. Furthermore, we investigated the relationship between the satellite data (vegetation index) and in situ tree-measurement data (leaf area index) to develop a simple model to directly map the tree leaf area from the WorldView-2/3 imagery. The estimated total leaf area in Tokyo urban area in the leaf-on season (633 km²) was twice that of the leaf-off season (319 km²). Our results also showed that the estimated total leaf area in Tokyo urban area was 1.9–6.2 times higher than the results of the moderate-resolution (30 m) satellite imagery.