Gaofeng Fan

Understanding the response of tropospheric ozone (O₃) to nitrogen dioxide (NO₂) change is important for local O₃ control. The relationship between O₃ and NO₂ at county scale in China has been extensively studied using models, but there is a lack of results from direct measurements. In this study, we used measurements of O₃, NO₂ and meteorological conditions from a dense network in the Yangtze River Delta (YRD), and satellite observed formaldehyde (HCHO) and NO₂ column densities for the analysis of O₃ variabilities and its relationship to NO₂. As a result, severe O₃ pollution occurred mainly in Shanghai city, southern Jiangsu and northern Zhejiang provinces in YRD during April–September. In addition, meteorological conditions could explain 54% the diurnal O₃ variation over YRD. During April–September 2015–2021, O₃ showed a significant positive relationship (r = 0.61 ± 0.10) with NO₂ after removing the impact from meteorological conditions. However, the relationship could be reversed with NO₂ concentration change. Our result suggested that the controllable O₃ related to NO₂ change is up to 100 μg·m⁻³ in megacities over Shanghai and northern Zhejiang province. The O₃ is much more sensitive to the NO₂ reduction in megacities than surrounding areas. Our results evaluate the different impacts of NO₂ changes on O₃ formation, which provides explanation for the simultaneously alleviated O₃ pollution and reduced NO₂ in 2020 in Shanghai and northern Zhejiang, as well as the increased O₃ in most counties before 2019 with reduced NO₂ during October–March. The driving mechanism as revealed from this study for O₃ and NO₂ will be valuable for the O₃ abatement through NO₂ reduction at sub-county scale over YRD in China.

In the context of global warming, how to measure summer climate suitability at a local scale is important for meteorological services. Considering meteorological and ecological conditions, body comfort, and the atmospheric environment, an assessment method for summer climate suitability for Zhejiang Province is proposed. In this paper, a summer suitable index (SSI) for Zhejiang is calculated, including four secondary indices: a summer cool index (SCI), a comfort days index (CDI), a good air days index (GADI) and a vegetation cover index (VCI). Using a local evaluation criterion, summer climate suitable areas are distinguished objectively according to the SSI. The results show that especially suitable regions account for 4.97% of Zhejiang Province, very suitable regions account for 22.2%, suitable regions account for 39.58%, and general regions account for 33.25%. The summer climate suitable areas are located mainly in high mountains and hills and coastal island areas while plain areas cannot be considered a suitable destination for summer tourism. By comparison and discussion, the SSI is demonstrated to capture summer climate suitability well. In contrast to a fixed evaluation index, benchmark values obtained for the SSI depend on the local climate and the index is straightforward to apply.

Since preindustrial times, atmospheric CO₂ content increased continuously, leading to global warming through the greenhouse effect. Oceanic carbon sequestration mitigates global warming; on the other hand, oceanic CO₂ uptake would reduce seawater pH, which is termed ocean acidification. We perform Earth system model simulations to assess oceanic CO₂ uptake, surface temperature, and acidification for Zhejiang offshore, one of the most vulnerable areas to marine disasters. In the last 40 years, atmospheric CO₂ concentration increased by 71 ppm, and sea surface temperature (SST) in Zhejiang offshore increased at a rate of 0.16°C/10a. Cumulative oceanic CO₂ uptake in Zhejiang offshore is 0.3 Pg C, resulting in an increase of 20% in sea surface hydrogen ion concentration, and the acidification rate becomes faster in the last decade. During 2020–2040, under four RCP scenarios, SST in Zhejiang offshore increases by 0.3–0.5°C, whereas cumulative ocean carbon sequestration is 0.150–0.165 Pg C. Relative to RCP2.6, the decrease of surface pH in Zhejiang offshore is doubled under RCP8.5. Furthermore, simulated results show that the relationship between CO₂ scenario and oceanic carbon cycle is nonlinear, which hints that deeper reduction of anthropogenic CO₂ emission may be needed if we aim to mitigate ocean acidification in Zhejiang offshore under a higher CO₂ concentration scenario. Our study quantifies the variation characteristics of oceanic climate and carbon cycle fields in Zhejiang offshore, and provides new insight into the responses of oceanic carbon cycle and the climate system to oceanic carbon sequestration.

This work investigates the effect of the resampling spatial resolution (RSR) on the retrieval of ocean surface wind speed from satellite-borne Synthetic Aperture Radar (SAR) images. For this purpose, 358 RADARSAT-2(RS-2) fine-beam quad-polarized SAR images and in-situ National Data Buoy Centre (NDBC) and China State Oceanic Administration (SOA) buoy measurements from selected geographic locations are used in this paper. In order to obtain better accuracy SAR-retrieved wind speeds, CMOD5.N function, Z2011 polarization ratio (PR) model and C2PO model constitute the best models for VV-, HH- and cross-polarized SAR images, respectively. The resulting statistical analysis suggests that better accuracy wind speeds can be retrieved at somewhat coarser resolutions. The optimal RSR for the VV-, HH-, VH- and HV-polarized channels are 850, 1050,1350 and 1450 m, respectively, with RMSEs of 1.74, 2.03, 1.61 and 1.83 m/s.

A typhoon is one of the most dangerous natural disasters in the Yangtze River Delta of China. Based on an integrated assessment of the disaster risk elements, including hazard factor, exposure, and vulnerability, the risk level of a typhoon disaster for the Yangtze River Delta as a county-level unit was ultimately determined. The result shows that the risk levels of typhoon hazard factor are gradually weakened from the southeastern coastal areas to the northwest, and the highest-risk areas are located in the southeastern coastal regions. Due to many towns, dense population, a developed economy, and a huge disaster-bearing body in the north of the Yangtze River Delta, which is also located on the plain for a high susceptibility to a disaster-breeding environment, the exposure risk level in the northern areas is higher than in the south. The most vulnerable counties are Chun'an, Xianju, Tiantai, and Sanmen in Zhejiang Province, and Baoying and Xinghua in Jiangsu Province. The highest-risk areas for a typhoon disaster are primarily located in the southeastern coastal areas of Zhejiang Province, Hangzhou Bay, and Shanghai near the Yangtze River Estuary, while the lowest-risk areas are distributed in the western portion of Hangzhou and the northern area of the Yangtze River Delta.