Particulate air pollution has been suggested as the cause of the recently observed decreasing trends of 10 to 25% in the ratio between hilly and upwind lowland precipitation, downwind of urban and industrial areas. We quantified the dependence of this ratio of the orographic-precipitation enhancement factor on the amounts of aerosols composed mostly of pollution in the free troposphere, based on measurements at Mt. Hua near Xi'an, in central China. The hilly precipitation can be decreased by 30 to 50% during hazy conditions, with visibility of less than 8 kilometers at the mountaintop. This trend shows the role of air pollution in the loss of significant water resources in hilly areas, which is a major problem in China and many other areas of the world.
Aristolochia subgen. Siphisia, comprising 98 species, is mainly distributed in East and South Asia, with some scattered in North and Central America. It has often been recognized as one of three subgenera of Aristolochia and can be distinguished from both remaining subgenera (Aristolochia subgen. Aristolochia and Aristolochia subgen. Pararistolochia) by morphological synapomorphies such as a strongly curved perianth with a 3-lobed limb, and especially the 3-lobed gynostemium, anthers paired on the outer surface of each gynostemium segment. However, recent cladistic analyses based on morphological characters and molecular data suggested that Aristolochia s.l. should be divided into four genera in two subtribes. In this study, a comprehensive analysis of molecular data of two plastid genic spacers (rps16-trnK and petB-petD), and two nuclear genes (phyA and ITS2) with an extensive sampling of Asian and American species was conducted. The combined datasets confirmed that Aristolochia subgen. Siphisia should be treated as an independent genus. Then Isotrema is reinstated here with 87 new combinations for the most comprehensive enumeration.
The characteristics of the planetary boundary layer height (PBLH) and the relationship between PBLH and particular matter (PM) mass concentration in Xi'an, central China, are analyzed in this study. Three PBLH calculation methods are used in this study, namely the Holzworth, Liu, and Nozaki approaches. The daily minimum and maximum PBLHs are determined by the Holzworth method, the hourly PBLHs are calculated by the Nozaki method, and the results of the Nozaki method are evaluated by the Liu method. The PBLH characteristics of annual, seasonal, daily, and diurnal variations are based on hourly values obtained from the Nozaki method. The results show that the Nozaki method can depict typical PBLH diurnal variations, although it substantially overestimates the related values. The daily maximum PBLH occurs from 11:00 to 16:00 Beijing time, and the seasonal maximum PBLH is during spring, due to the annual maximum wind speed at this time. PM 2.5 , PM 1.0 and PM 10 mass concentrations are negatively correlated with PBLH on the inter-annual, annual, and seasonal time scales. The anti-phase diurnal variations of PM mass concentrations and PBLH further indicate that PBLH is one of the important factors affecting air quality. The PM 2.5 in PM 10 , PM 1.0 in PM 2.5 , and PM 1.0 in PM 10 contents show notable monthly variations, indicating that the air quality in Xi'an city is affected upwind windy and dusty weather, along with local pollution sources.
From 2000 to 2019, 11,895 new names or new additions to the Chinese vascular flora were proposed by 4226 individuals (4086 articles and 140 books), as documented in the Chinese Plant Names Index (CPNI). During those 20 years, 4407 new taxa of vascular plants were described from China, including 7 new families, 132 new genera, 3543 new species, 68 new subspecies, 497 new varieties and 160 new forms. Additionally, 3562 new combinations and names at new rank and 306 new replacement names were also proposed. Among these various new names were 150 invalid names and 108 illegitimate names, including some that have not been resolved. Six hundred and forty three vascular plants were reported as new to China, while 2349 names were reduced to synonyms of 1406 taxa. The data show that the Chinese flora increased in size at the rate of about 200 taxa annually during those years. Despite the increased attention given to biodiversity in recent years, the evidence indicates that a large number of species in China have yet to be discovered. Further basic investigation of the Chinese flora is needed. Additionally, in the past two decades only 8.5% of the newly published species have been based on molecular evidence, but in the past five years such data have increased significantly, reaching about 20%. Molecular data will undoubtedly become increasingly significant in the discovery of new species in the coming years. Yunnan, Guangxi, Sichuan, Xizang and Taiwan were important sources of new discoveries, with more than 3300 new taxa and records from these five provinces. By area, Taiwan and Hainan, two islands in southern China, have the highest density of newly discovered species. Regional plant surveys are still needed, especially in areas in the southwest and on the southern islands.
Abstract:The formation of new atmospheric aerosol particles and their subsequent growth have been observed under different environmental conditions globally; such observations are few over northwest China. Here, we present an analysis of some case studies for new particle formation (NPF) events from two distinct suburban locations in northern China during May and June of two consecutive years, and provide more information to understand the characteristics of NPF events in North China. Particle number size distribution was measured at suburbs of Beijing (39.75 • N, 116.96 • E) during 1 June to 2 July 2013 and at suburbs of Xi'an (34.09 • N, 108.55 • E) during 1 to 25 May 2014. The average of total particle number concentration in the similar size range of 10-487 nm at the suburbs of Beijing (9.0 × 10 3 cm −3 ) was about two times higher than those observed at Xi'an (4.7 × 10 3 cm −3 ), and the mean particle mode diameter at Beijing was 1.4-fold higher than that at Xi'an. The estimated total condensation sink (CS) at Beijing (3.11 × 10 −2 s −1 ) was also higher than at Xi'an (1.13 × 10 −2 s −1 ). The frequency of NPF events at suburb of Beijing was 24%, lower than that in Xi'an (50%), and also lower than urban site of Beijing (35% in June) and another suburb of Beijing (over 50% in June). The NPF events with (Class I) or without (Class II) subsequent growth were both observed at the two suburb sites. The derived GR at the suburb of Beijing (range from 4.6 to 8.6 nm h −1 ) was a little higher than that at Xi'an (range from 3.3 to 6.7 nm h −1 ), which are generally comparable to typical values in mid-latitude reported in previous studies. The air masses coming from north or northwest China favor the occurrence of NPF event under low condensation sink and clear days. The number size distributions of freshly nucleated particles showed clear bimodal distributions on both sites. Additionally, Mode D p of nucleated particles at the two sites was 17 ± 1 nm and 22 ± 4 nm, respectively during the periods with NPF events. The case study of NPF events at the two suburb sites shows that the surface area concentration and total scattering coefficient (SC) was significant decreased during the NPF events at both sites. High temperature, low condensation sink and low relative humidity furthered the occurrence of NPF events, and wind direction shifts were important for the subsequent growth of particles. NPF events in the suburbs of Beijing usually occurred when relative humidity (RH) < 55%, CS < 0.02 s −1 , or 55% < RH < 68%, CS < 0.01 s −1 . However, there is no clear range for Xi'an. Furthermore, we observed that some NPF events occurred at higher RH and very low CS in this study on both sites, which means that low CS may be more important than low RH for the particle formation on clear days.
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