The first Tropospheric Ozone Assessment Report (TOAR) provides information on present-day distributions and long-term trends of ozone metrics relevant for climate change, human health, and vegetation. However, only few results are available in TOAR for China due to limited long-term ozone observations. Here, we present an integrated analysis of long-term measurements of surface ozone from eight sites distributed in the North China Plain (NCP) and Yangtze River Delta (YRD), the relatively underdeveloped region Northeast China, and the remote regions in Northwest and Southwest China. Trends and present-day values for seven annual and five seasonal ozone metrics were calculated following the TOAR methodologies. We compare the seasonal and diurnal cycles of ozone concentrations as well as the present-day values of ozone among sites and discuss the long-term trends in the ozone metrics. Large and significant increases of ozone are detected at the background site in the NCP, moderate increases at the global baseline site in western China, significant decreases at the northwestern edge of China, and nearly no trend at other sites. Extremely high values of ozone occurred in the NCP and YRD, particularly in warmer seasons. The present-day levels of summer ozone metrics in the NCP are much higher than the thresholds set in TOAR for the highest value groups of ozone metrics. The summer ozone metrics at the Shangdianzi background site in the NCP indicate increases at rates of more than 2%/yr during 2004–2016. In contrast, ozone at the Lin’an background site in the YRD was constant over the period 2006–2016. Our results fill some knowledge gaps in spatiotemporal changes of ozone in China and may be of useful in the assessment of ozone impacts on human health and vegetation.

As the most economically developed region in China, the Yangtze River Delta (YRD) region contributed to ~17% of the total anthropogenic CO₂ emissions from China. However, the studies of atmospheric CO₂ and CH₄ in this area are relatively sparse and unsystematic. Here, we analyze the changing characters of those gases in different development periods of China, based on the 11-year atmospheric CO₂ and CH₄ records (from 2010 to 2020) at one of the four Chinese sites participating in the World Meteorological Organization/Global Atmospheric Watch (WMO/GAW) program (Lin’an regional background station), located in the center of YRD region, China. The annual average atmospheric CO₂ and CH₄ mole fractions at LAN have been increasing continuously, with growth rates of 2.57 ± 0.14 ppm yr⁻¹ and 10.3 ± 1.3 ppb yr⁻¹, respectively. Due to the complex influence of regional sources and sinks, the characteristics of atmospheric CO₂ and CH₄ varied in different periods: (i) The diurnal and seasonal variations of both CO₂ and CH₄ in different periods were overall similar, but the amplitudes were different. (ii) The elevated mole fractions in all wind sectors tended to be uniform. (iii) The potential source regions of both gases expanded over time. (iv) The growth rate in recent years (2016–2020) changed significantly less than that in the earlier period (2010–2015). Our results indicated that the CO₂ and CH₄ mole fractions were mainly correlated to the regional economic development, despite the influence of special events such as the G20 Summit and COVID-19 lockdown.

Trees are known to modify radiation on building façades via shading effects. However, the combined influence of tree morphological traits and street canyon geometry on façade solar exposure remains inadequately quantified. This paper will fill this gap by using an integrated field measurement, ENVI-met simulations and theoretical analysis of an east–west street canyon in Hangzhou, China. We present the stratified cumulative shortwave radiation disturbance (SRD) and the mean value (MSRD) of R as indices for assessing the influence of the tree height (TH), canopy diameter (D_C), leaf area density (LAD), and under-canopy height (UH) on the shortwave radiation profile of the south façade. Using 54 parametrized simulation scenarios, it was found that tree height is the most sensitive parameter to affect MSRD in the 1114 m range, with under-canopy height defining the building layers below. An LAD of 2 m²/m³ will be an optimal shading and daylighting. When discussed in terms of space, a canopy diameter of 5 m and a wall-to-canopy distance of 1 m (D_W-T) provides better shading in asymmetric canyons where the buildings in the south are lower. Further, canyon building height on either side of the canyon is found to be a decisive factor that mediates tree impacts on radiation, which allows specific approaches to greening canyons of diverse kinds. Through this work, there is a theoretical basis for understanding how trees and canyons interact, and this work gives scientific principles for a tree-planting initiative to reduce urban heat islands.