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Ye X.,Peking University | Wu B.,Tianjin Meteorological Administration | Zhang H.,Peking University
Atmospheric Research | Year: 2014

This paper investigates the vertical structure and turbulence activities in fog events. Three fog cases that occurred in the winter of 2010 over Tianjin, China were selected, including two advection-radiation fog events and an advection fog event. Field observations collected at a 255-m tall meteorological tower in Tianjin were analyzed, including turbulence measurements using the eddy covariance systems installed at three levels, measurements of temperature, horizontal wind and humidity collected at 15 levels, surface radiation fluxes and horizontal visibility. The results suggest that the advection fog was more enduring and thicker than the advection-radiation fog. The fog events were characterized by low wind speed throughout the fog layer. A temperature inversion and low-level jet were observed above the advection-radiation fog layer. The surface net radiation reflected some differences among the fog events. The collapse of turbulence was a necessity for the formation fog, and moderate turbulence was favorable to the development and maintenance. The heat and water vapor fluxes in the advection-radiation fog were weaker than those in the advection fog, in which the stratification was slightly unstable. The relationships among the turbulent transport efficiencies of water vapor, temperature and momentum were examined. The results suggest the applicability of local similarity in the fog layer for the momentum transport efficiency. © 2014 Elsevier B.V.

Han S.,Nankai University | Bian H.,Tianjin Meteorological Administration | Feng Y.,Nankai University | Liu A.,Tianjin Meteorological Administration | And 3 more authors.
Aerosol and Air Quality Research | Year: 2011

The continuous measurement of nitric oxide (NO), nitrogen dioxide (NO2), nitrogen oxides (NOx) and ozone (O3) was conducted in Tianjin from September 8 to October 15, 2006. The data were used to investigate the relationship between the O3 distribution and its association with ambient concentrations of NO, NO2 and NOx (NO and NO2). The measured concentrations of the pollutants in the study area varied as a function of time, while peaks in NO, NO2 and O3 all occurred in succession in the daytime. The diurnal cycle of ground-level ozone concentration showed a mid-day peak and lower nighttime concentrations. Furthermore, an inverse relationship was found between O3 NO, NO2 and NOx. In addition, a linear relationship between NO2 and NOx, as well as NO and NOx, and a polynomial relationship between O3 and NO2/NO was found. The variation in the level of oxidant (O3 and NO2) with NO2 was also obtained. It can be seen that OX concentration at a given location is made up of two parts: one independent and the other dependent on NO2 concentration. The independent part can be considered as a regional contribution and is about 20 ppb in Tianjin. An obvious difference in NO, NOx and O3 concentrations between weekdays and weekends was also found, but this difference did not appear in NO2. Lastly, the diurnal variation of O3 concentration under different meteorological conditions was demonstrated and analyzed. © Taiwan Association for Aerosol Research.

Tian Y.-Z.,Nankai University | Shi G.-L.,Nankai University | Han S.-Q.,Tianjin Meteorological Administration | Zhang Y.-F.,Nankai University | And 5 more authors.
Science of the Total Environment | Year: 2013

To investigate the vertical characteristics of ions in PM10 as well as the contributions and possible locations of their sources, eight water-soluble ions were measured at four heights simultaneously along a meteorological tower in Tianjin, China. The total ion concentrations showed a general decreasing trend with increasing height, ranging from 64.94μgm-3 at 10m to 44.56μgm-3 at 220m. NH4 +, SO4 2- and NO3 - showed higher height-to-height correlations. In addition, relationships between ions are discussed using Pearson correlation coefficients and hierarchical clustering analysis (HCA), which implied that, for each height, the correlations among NH4 +, SO4 2- and NO3 - were higher. Finally, sources were identified qualitatively by the ratio of certain ions and quantitatively by principal component analysis/multiple linear regression (PCA/MLR) and positive matrix factorisation (PMF). Secondary sources played a dominant role for PM10 and water-soluble ions at four heights and became more important at greater heights (the percentage contributions were 43.04-66.41% for four heights by PCA/MLR and 46.93-67.62% by PMF). Then, the redistributed concentration field (RCF) combined with PCA/MLR and PMF was applied, which indicated the high potential source regions. The vertical characteristics of the levels, relationships, source contributions and locations would support the effective management of the water-soluble ions in particulate matter. © 2012.

Shi G.-L.,Nankai University | Tian Y.-Z.,Nankai University | Han S.-Q.,Tianjin Meteorological Administration | Zhang Y.-F.,Nankai University | And 5 more authors.
Atmospheric Environment | Year: 2012

In this work, two new chemical mass balance (CMB) models were applied to estimate the possible source contributions to organic carbon (OC) and the secondary OC (SOC) concentrations in PM 10 at 10, 40, 120 and 220 m heights on a meteorological tower in Tianjin. The OC and EC (elemental carbon) were simultaneously measured at the four heights from 24 August to 12 September 2009. The vertical characteristics of OC and EC showed a general decreasing trend with the increasing height. The SOC concentrations were then estimated by the minimum OC/EC ratio method, the NCPCRCMB model and the CMB-Iteration method. The results suggest increasing trends for SOC/TOC and SOC/PM 10 up the tower. Additionally, wind rose maps and hourly 72-h back trajectory cluster maps were combined with the source apportionment results to discuss the vertical source contributions to OC, indicating that the percentage contributions of long-range transport sources (such as soil dust and SOC sources) increased with height. SOC formation and transportation by wind affected OC more strongly than each primary source at greater heights. Finally, the levels and sources of the excess OC (the difference between OC concentrations at lower heights to that at 220 m) are discussed. The results suggest that it is more effectively managed for reducing OC to control vehicle and coal sources at the ground level in Tianjin. Information about the more significant sources of excess OC can be used for the development of effective control strategies. © 2012 Elsevier Ltd.

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