Jinsen Shi

Black carbon in seasonal snow across northern Xinjiang in northwestern China

Black carbon (BC) particles in snow can significantly reduce the snow albedo and enhance the absorption of solar radiation, with important impacts on climate and the hydrological cycle. A field campaign was carried out to measure the BC content in seasonal snow in Qinghai and Xinjiang provinces of western China, in January and February 2012. 284 snow samples were collected at 38 sites, 6 in Qinghai and 32 in Xinjiang. The observational results at the sites in Xinjiang, where the absorbing impurities in snow are dominated by BC particles, are reported in this work. The BC mass fractions in seasonal snow across northern Xinjiang have a median value of ~70 ng g−1, much lower than those in northeast China. The estimated concentration of BC at the cleanest site in Xinjiang is 20 ng g−1, which is similar to that found along the coast of the Arctic Ocean. It is found that the BC content of snow decreases with altitude. Taking into account this altitude dependence, our measured BC contents in snow are consistent with a recent measurement of BC in winter snow on Tianshan glacier. The data from this field campaign should be useful for testing transport models and climate models for the simulated BC in snow.

A comparison of the physical and optical properties of anthropogenic air pollutants and mineral dust over Northwest China

Emissions of mineral dust and its mixing with anthropogenic air pollutants affect both regional and global climates. Our fieldwork in late spring 2007 (April 25–June 15) measured the physical and optical properties of dust storms mixed with local air pollutants at a rural site about 48 km southeast of central Lanzhou. Levels of air pollutants and aerosol optical properties were observed during the experiment, with concentrations of NOx (6.8 ± 3.3 ppb, average ± standard deviation), CO (694 ± 486 ppb), SO2 (6.2 ± 10 ppb), O3 (50.7 ± 13.1 ppb), and PM10 (172 ± 180 μg m−3), and aerosol scattering coefficient (164 ± 89 Mm−1; 1 Mm = 106 m) and absorption coefficient (11.7 ± 6.6 Mm−1), all much lower than the values observed during air pollution episodes in urban areas. During a major dust storm, the mass concentration of PM10 reached 4072 μg m−3, approximately 21-fold higher than in non-dust storm periods. The mixing ratios of trace gases declined noticeably after a cold front passed through. The observed CO/SO2 and CO/NOx ratios during air pollution episodes were 4.2–18.3 and 13.7–80.5, respectively, compared with the corresponding ratios of 38.1–255.7 and 18.0–245.9 during non-pollution periods. Our investigations suggest that dust storms have a significant influence on air quality in areas far from their source, and this large-scale transport of dust and air pollutants produces major uncertainties in the quantification of the global effects of emissions over Northwest China.

Measurement of scattering and absorption properties of dust aerosol in a Gobi farmland region of northwest China — a potential anthropogenic influence

We conducted a comprehensive field campaign to explore the optical characteristics of mineral dust in Dunhuang farmland near the Gobi Desert of northwest China during spring of 2012. The day-to-day and diurnal variations of dust aerosol showed prominent features throughout the experiment, primarily attributable to frequent dust events and local anthropogenic emissions. The overall average mass concentrations of the particulate matter with an aerodynamic diameter less than 10 μm (PM10), light scattering coefficient (σsp,670), absorption coefficient (σap,670), and single-scattering albedo (SSA670) were 113± 169 μg m−3, 53.3± 74.8 Mm−1, 3.2± 2.4 Mm−1, and 0.913± 0.05, respectively, which were comparable to the background levels in the southern United States but smaller than those in the eastern and other northwestern Chinese cities. The anthropogenic dust produced by agricultural cultivations (e.g., land planning, plowing, and disking) exerted a significant superimposed effect on high dust concentrations in Dunhuang farmland prior to the growing season (i.e., from 1 April to 10 May). Strong south valley wind and vertical mixing in daytime scavenged the pollution, and the weak northeast mountain wind and stable inversion layer at night favorably accumulated the air pollutants near the surface. In the afternoon (13:00–18:00 LT, local time), mean SSA670 was 0.945± 0.04 predominantly from dust particles, whereas finer particles and lower SSA670 values (∼ 0.90–0.92) were measured at night, suggesting the potential influence by the mixed dust pollutants. During a typical biomass burning event on 4 April 2012, σap,670 increased from ∼ 2.0 to 4.75 Mm−1 and SSA670 changed from ∼ 0.90 to ∼ 0.83, implying remarkable modification of aerosol absorptive properties induced by human activities. The findings of this study would help to advance an in-depth understanding of the interaction among dust aerosol, atmospheric chemistry, and climate change in a desert source region.

Automated detection of cloud and aerosol features with SACOL micro-pulse lidar in northwest China

The detection of cloud and aerosols using a modified retrieval algorithm solely for a ground-based micropulse lidar (MPL) is presented, based on one-year data at the Semi-Arid Climate Observatory and Laboratory (SACOL) site (35.57°N, 104.08°E, 1965.8 m), northwest of China, from March 2011 to February 2012. The work not only identifies atmosphere particle layers by means of the range-dependent thresholds based on elastic scattering ratio and depolarization ratio, but also discriminates the detected layers by combining empirical thresholds of the atmospheres thermodynamics states and scattering properties and continuous wavelet transform (CWT) analyses. Two cases were first presented in detail that demonstrated that the modified algorithm can capture atmosphere layers well. The cloud macro-physical properties including cloud base height (CBH), cloud geometrical thickness (CGT), and cloud fraction (CF) were then analyzed in terms of their monthly and seasonal variations. It is shown that the maximum/minimum CBHs were found in summer (4.66 ± 1.95km)/autumn (3.34 ± 1.84km). The CGT in winter (1.05 ± 0.43km) is slightly greater than in summer (0.99 ± 0.44km). CF varies significantly throughout year, with the maximum value in autumn (0.68), and a minimum (0.58) in winter, which is dominated by single-layered clouds (81%). The vertical distribution of CF shows a bimodal distribution, with a lower peak between 1 and 4km and a higher one between 6and 9km. The seasonal and vertical variations in CF are important for the local radiative energy budget.

Tribological study of nitrogen implanted niobium

Abstract Niobium single crystals with (111) orientation were implanted by 110 keV nitrogen ions up to a dose of 5 × 10 17 ions cm −2 at a temperature less than 100 °C. Before and after the implantation, tribological properties involving microhardness, friction coefficient and wear rate against hardened GCr15 steel ball were determined. The wear tracks and the scars were also examined by scanning electron microscopy and an electron probe micro-analyzer. The structure of the implanted layer was characterized by glancing-angle X-ray diffraction. The results showed that the 110 keV nitrogen implantation led to an increase of 18.5% in microhardness and big reductions of both friction coefficient (from unimplanted 0.95 to implanted 0.20 ∼ 0.21) and wear rate (from 2.8 × 10 −7 to 1.1 × 10 −7 mm 3 mm −1 ). For the unimplanted niobium, features indicating adhesion and/or severe wear were observed on wear tracks, while for the implanted niobium, only parallel grooves and microcracks with higher Fe content were formed on wear tracks. The tribological improvement was explained in terms of implantation-induced formation of niobium nitrides which was revealed by glancing-angle X-ray diffraction analysis.

Nitrogen ion implantation for the surface modification of 9Cr18Mo steel

Abstract The effect of nitrogen ion implantation on the electrochemical and fretting behavior of 9Cr18Mo steel has been studied. Anodic polarization measurement in a 0.1N sulphuric acid solution was used to evaluate the corrosion resistance of the steel before and after nitrogen ion implantation. Lower passive current density and higher corrosion potential were obtained on the implanted specimens. The best effect was observed on the fourth polarization scan in multipolarization tests, which correlated well with the nitrogen concentration depth profile determined by AES. The variation of corrosion current density vs corrosion time was also tested. The corrosion current density of the implanted specimen is two orders of magnitude lower than that of the unimplanted specimen, indicating that the corrosion rate of the implanted surfaces is much lower. Fretting tests were also used to evaluate the effect of nitrogen ion implantation. The fretting resistance was clearly improved after implantation.