Ground-level ozone (O₃) pollution has been a severe environmental and health problem for decades. The importance of biogenic volatile organic compounds (BVOCs) in the formation of tropospheric photochemistry O₃ has been highlighted, especially in areas of rapid urbanization. We conducted simultaneous measurements of trace gases, including NO, NO_X, O₃, and BVOCs (i.e., isoprene and α-pinene), in the urban and rural forest areas of Beijing to determine the relationships between them. The results highlight the differences between the urban and rural forest areas of Beijing in terms of ambient air concentrations of BVOCs and O₃, and the interrelationships between BVOCs, NO_X, and ozone were quantified. Moreover, the isoprene concentration was found to be higher in the atmosphere of the urban site than of the rural site, which had higher α-pinene concentrations and higher O₃ concentrations. The NO_X concentration was higher at the urban site than at the rural site, and there was a significant exponential relationship between NO_X and O₃ at the urban site, indicating that the impact of NOx on O₃ at the urban site was greater than that at the rural site. The O₃ concentration increased with rising isoprene and α-pinene in both sites. In the case of substantially increased BVOC concentrations, declining NO_X concentrations strongly promote the formation of O₃. Consideration should be given to planting tree species with low-BVOC emissions, as they are crucial for mitigating O₃ pollution in urban areas. Additionally, the relationships between BVOCs, NO_X, and O₃ should be considered in policymaking related to O₃ control.

In this study, we aim to carry out a coupling analysis of the thermal landscape and environmental carrying capacity of urban expansion in Beijing over the past 35 years to provide scientific grounding for city planning. The paper proposes a conceptual framework and develops an integrated quantitative approach to the coupling analysis between urban expansion, the urban ecological environment, and the urban landscape, including the Urban Eco-Environment Carrying Capacity Index (ECI), Landscape Spatial Structure Index, Landscape Thermal Index (LTI), and Transitional Landscape Index (TLI, Markov Chain Model). Urban expansion has been essentially dominated by policy adjustments and has been further influenced by socioeconomic development, which has contributed to four outbreaks of urban sprawl in Beijing. Urban expansion is an essential factor affecting ecological environment change. The Olympic Games in 2008 was the turning point for the urban landscape. The rate of urban expansion and improvement of the ecological landscape all changed significantly around the year 2008. The urban thermal distribution pattern coincided well with the featured landscape patches, representing an obvious reflection of the difference between urban green spaces and construction, while high-temperature areas were abundant in the urban center. Urban expansion has a positive effect on the ecological environment and landscape pattern when it is fully matured and well planned. It is expected that, by 2025, the ecological environment of Beijing will be significantly improved, and the proportion of high-temperature areas will decrease.

Despite the importance of landscape design and water-resources management for urban planning, urban-forest transpiration was seldom estimated in situ. Detailed data on different urban trees’ water resource use and the effect of climatic fluctuations on their transpiration behaviour in different timescales are limited. In this study, we used a thermal dissipation method to measure the sap flux density (J_s) of three urban tree species (Pinus tabulaeformis Carrière, Cedrus deodara (Roxb.) G. Don, and Robinia pseudoacacia Linn.) from 1 May 2008 to 30 April 2016 in Beijing Teaching Botanical Garden. The effects of environmental factors on sap flux density (J_s) in different timescales were also analyzed. The results showed that there were significant differences in the sap flux density of three trees species in daily, seasonal, and interannual timescales. The hourly, seasonal, and interannual mean sap flux density of Pinus tabulaeformis were higher than that of Cedrus deodara and Robinia pseudoacacia. The seasonal mean J_s of Pinus tabulaeformis, Cedrus deodara, and Robinia pseudoacacia in summer were 18.67, 16.19, and 41.62 times that in winter over 2008–2015. The annual mean sap flux density of Pinus tabulaeformis was 1.25–1.72 and 1.26–1.82 times that Cedrus deodara and Robinia pseudoacacia over 2008–2015. The J_s responses in three tree species to environmental factors varied differently from daily to interannual timescales. The pattern of day-to-day variation in J_s of three urban tree species corresponded closely to air temperature (T_a), soil temperature (T_s), solar radiation (R_s), and vapor pressure deficit (VPD). The Jarvis–Stewart model based on T_a, R_s, and VPD was more suitable for the sap flux density simulation of Pinus tabulaeformis than Cedrus deodara and Robinia pseudoacacia. The main factor affecting the sap flux density of Pinus tabulaeformis and Cedrus deodara was T_a in seasonal timescales. However, the main factor affecting the sap flux density of Robinia pseudoacacia was T_s. The interannual variations in the J_s of Pinus tabulaeformis and Robinia pseudoacacia were mainly influenced by wind speed (w) and soil water content (SWC), respectively. The selected environmental factors could not explain the variation in the sap flux density of Cedrus deodara in an interannual timescale. The findings of the present study could provide theoretical support for predicting the water consumption of plant transpiration under the background of climate change in the future.

The intermittent ozone (O₃) exposure of crops to alternating high and low concentrations is common in fields, but its impact on crop production has not been thoroughly investigated. In this study, two widely planted and O₃-sensitive crops, winter wheat and soybean, were intermittently exposed to elevated O₃ concentrations in open-top chambers. The results showed that the winter wheat and soybean yields significantly decreased with O₃ exposure (AOT40, cumulative hourly O₃ concentration above 40 ppb) (p < 0.001). The relative yield losses were 0.99% per AOT40 for winter wheat and 1.2% per AOT40 for soybean, respectively. The responses of the crop biomasses to elevated O₃ concentrations were lower than that of crop yield. Although the O₃-induced crop yield and biomass losses under continuous O₃ exposure were greater than those under intermittent O₃ exposure, the differences were not statistically significant. Therefore, we can conclude that the effects of elevated O₃ concentrations on crops are closely related to the exposure dose but not significantly related to the temporal distribution of elevated O₃ concentrations. This study improves our understanding of how crop production responds to intermittent O₃ exposure.

In this paper, the variation characteristics of diurnal and weekly transportation CO₂ emissions at intersection of the Datun and Beichen West Road are studied from the urban road scale. The double-peak and double-trough pattern of diurnal transportation CO₂ emissions at the intersection of Datun Beichen West Road is very obvious. The weekly transportation CO₂ emissions order is: Monday (the first workday of a week) > weekend > Wednesday (an ordinary workday of a week). Based on this, transportation carbon emission reduction is proposed in this paper.