Three-dimensional building morphology impacts on PM2.5 distribution in urban landscape settings in Zhejiang, China.

Three-dimensional (3D) urban landscape patterns and building morphology are crucial for urban planning and essential for urban landscape functions. In this study, fixed and mobile monitoring sites were used to determine the spatial distribution of PM2.5 concentrations in Hangzhou. Six 3D metrics were selected to analyze the response of PM2.5 pollution to landscape patterns and building morphology, while their two-dimensional (2D) counterparts' metrics were also analyzed to contrast the differences. A variance partitioning analysis (VPA) was performed to measure the combined and relative contribution of 3D and 2D metrics to the changes in PM2.5 concentrations. The results showed that: (1) on the 3D scale, forming a building pattern with a combination of different building heights can eliminate the accumulation of PM2.5; (2) on the 2D scale, fragmentation and decentralization of landscapes and building patches alleviate PM2.5 pollution; and (3) 3D building morphology indicators have the highest explanatory power (40.94%) for the changes of PM2.5 concentrations. It turns out that the explanatory power of 3D metrics for PM2.5 concentrations changes is much greater than that of 2D metrics. In addition, when compared to building morphology indicators from a single dimension, the combination of 2D and 3D metrics is better able to reflect urban PM2.5 pollution. The results of this study expand our understanding of how PM2.5 pollution responds to 2D and 3D metrics and provide useful information for urban planning.

The legacy effects of PM2.5 depositon on Nerium Oleander L.

Green plants have the capability to retain atmospheric particulate matter (PM) on their leaves, which can effectively reduce PM pollution, especially in the urban settings. Some studies reported that the periodic PM pollution could change plant retaining PM capacity, which, indeed, was the reason of physiological responses. In advancing the previous studies, we selected Nerium oleander L. to measure PM retention on leaf surface in a controlled environment by the following periods: initial pollution period (S1), recovery period (R), and secondary pollution period (S2) for a total of 12 weeks. The experimental design was one elevated pollution treatment (166 µg m-3) and one ambient control (28 µg m-3) with three replications. Results showed that during S2, the total retention decreased by 8.87 µg cm-2, which was about 10.4% significant lower than in S1. During the third week, the ascorbic acid content (ASA) in S1 was 6.71 mg g-1 significantly lower than that in S2 in the treatment. The total chlorophyll (Chl T) of the treatment decreased continuously and significantly by 33.8% in S1, but showed no similar trend in S2. The net photosynthetic rate of the treatment was significantly lower than that of the control, and the plants in the treatment showed a consistently high dark respiration rate than that in the control. The correlations between PM retention and ASA, Chl T and RWC were weaker in S1 than that in S2. In addition, air pollution tolerance index (APTI) showed a significant decline in plant pollution tolerance in the treatment during the third week.

Dynamics of particle retention and physiology in Euonymus japonicus Thunb. var. aurea-marginatus Hort. with severe exhaust exposure under continuous drought.

Frequent drought events and particulate matter pollution from vehicular exhaust seriously affect urban plant growth and provisioning of ecological services. Yet, how plants respond physiologically and morphologically to these two combined stressors remains unknown. Here, we assessed particle retention dynamics and plant morphology and physiology of Euonymus japonicus Thunb. var. aurea-marginatus Hort. under continuous drought with severe exhaust exposure. Our results showed that continuous drought insignificantly lowered particle retention in each of three size fractions by 1.02 µg·cm-2 on average in the first 28 days, but significantly lowered total particle retention by 35.75 µg·cm-2 on the 35th day. We observed evident changes in morphology, leaf mass per area (LMA), pigments, gas exchange in all stressed plants. Compared with single stress, combined drought and pollution caused earlier yellowing and shedding of old leaves, significantly lowered LMA by 1.21 mg·cm-2, caused a greater decline in pigments and net photosynthetic rate (Pn). Large particles may mainly explain pigment reduction, lower weekly LMA increases, and stomatal restriction, while coarse particles may be the main drivers of the decline in Pn. Continuous drought mediated the influence of all three particle sizes on some parameters, such as weakening the impact of total particles on LMA, strengthening the impact of fine particles on photosynthesis. Our findings suggest that drought accelerates the physiological responses of plants to exhaust pollution. Under controlled severe exhaust pollution conditions, the optimal time to maintain high particle retention during continuous drought without decline in physiological conditions for E. japonicus var. aurea-marginatus was 14 days. Some additional interventions after 14 days (it could be postponed appropriately under field conditions) may help ensure healthy growth of plants and retention of particulate matter.

Automobile exhaust particles retention capacity assessment of two common garden plants in different seasons in the Yangtze River Delta using open-top chambers.

Particulate matter (PM) pollution is a serious environmental problem in most of the cities in the Yangtze River Delta region. Plants can effectively filter ambient air by adsorbing PM. However, only a few studies have paid attention to the dynamic changes and seasonal differences in particle retention capacities of plants under long-term pollution. In this study, we investigated the dynamic changes in particle retention capabilities of the evergreen, broad-leaved, greening plants-Euonymus japonicus var. aurea-marginatus and Pittosporum tobira-in spring and summer. We employed an open-top chamber to simulate the severity of the tail gas pollution. The results showed that, both the plants reached a saturated state in 18-21 days, under continuous exposure to pollution (daily concentration of PM2.5: 214.64 ± 321.33 µg·cm-3). This was 6-8 days longer than that in the field experiments. In spring, the maximum retention of total particulate matter per unit leaf area of E. japonicus var. aurea-marginatus and P. tobira was 188.47 ± 3.72 µg cm-2 (18 days) and 67.63 ± 2.86 µg cm-2 (21 days), respectively. In summer, E. japonicus var. aurea-marginatus and P. tobira reached the maximum retention of the particle on the 21st day, with a net increase of 94.10 ± 3.77 µg cm-2 and 27.81 ± 3.57 µg cm-2, respectively. Irrespective of season, the particle retention capacity of E. japonicus var. aurea-marginatus was higher than that of P. tobira, and it showed a better effect on reducing the concentration of fine particles in the atmosphere. The particle retention of the two plants was higher in spring than that in summer. E. japonicus var. aurea-marginatus displayed a significant difference in particle retention between the seasons, while P. tobira did not show much difference. These results will provide a foundation for future studies on the dynamic changes and mechanism of particle retention in plants and management practices by employing plants for particle retention in severely polluted areas.