Li Y.,Meteorological Observation Center |
Zhao H.,Institute of Atmospheric Environment |
Wu Y.,CAS Institute of Atmospheric Physics
Aerosol and Air Quality Research | Year: 2015
Mass concentrations of particulate matter (PM), including PM1.0, PM2.5 and PM10, were measured from October 13th to November 30th 2013 at eight sites in Northeast China to evaluate their variations during pollution periods. Five major pollution periods were identified during the autumn of 2013. The maximum daily average PM2.5 concentrations were 437 ± 85 μg/m3 and 322 ± 50 μg/m3 in Harbin and Shenyang, respectively. The minimum was 75 ± 28 μg/m3 in Dandong. The presence of finer particles was significantly related to visibility degradation during pollution periods. Wind speeds had a negative correlation with PM concentrations, while high relative humidity (RH) favored the formation of haze in Northeast China. Visibility on non-hazy days was approximately 2.5–3.0 times greater than that on hazy days. During hazy days, the PM1.0:PM2.5 ratios were 0.89 ± 0.04, 0.85 ± 0.04 and 0.91 ± 0.04 at Anshan, Shenyang and Dandong, respectively. These results show that PM1.0 was the dominant particle pollutant in Northeast China during periods of pollution. High RH and low wind speeds during hazy days may favor the accumulation of atmospheric pollutants. The results of this study provide useful information toward recognizing air pollution episode characteristics in Northeast China. © Taiwan Association for Aerosol Research.
Li X.,Institute of Atmospheric Environment |
Zhang H.,Peking University
Aeolian Research | Year: 2015
Particle size distributions (psds) of airborne dust (PM20) during different dust emission events are investigated in this study, using data obtained from a dust-event monitoring station in the Horqin Sandy Land in Inner Mongolia, China. The results show that for a weak saltation-bombardment and aggregate-disintegration dust emission (SADE) event (0.44*<0.47ms-1) on 7 April 2012, dust aerosols ≤1μm in diameter (d) accounted for 80% for all dusts measured. While for a strong SADE event (0.85*<0.89ms-1) on the same day, large dust aerosols (d≥2.5μm) increased significantly, with the largest proportion (40%) located in 4-7μm, which agreed with the airborne dust psds observed during another two strong SADE events (mean u*=0.78 and 0.68ms-1) on 13-14 April 2013. However, for a convective turbulent dust emission (CTDE) event (mean u*=0.31ms-1) on 17 April 2013, the mean proportion of dust aerosols <0.45μm reached 70%, which suggests that only fine dust particles loosely distributed at the surface could be easily uplifted into the atmosphere by convective turbulence. It found that the airborne dust psds at emission move to the larger sizes with the increasing u*, but they remain unchanged when u* doesn't change too much. In addition, the dust psds for a non-local dust event on 19 April 2012 appeared smoother because of the mixing of dust aerosols through the processes of dust advection and deposition. © 2015 Elsevier B.V.
Yin H.,Peking University |
Li Z.,Peking University |
Li Z.,Key Laboratory of Resources Remote Sensing and Digital Agriculture |
Wang Y.,Peking University |
Cai F.,Institute of Atmospheric Environment
Acta Geographica Sinica | Year: 2011
Desertification is one of the serious threats to the environment in arid and semi-arid northern China. In order to understand inter-annual vegetation dynamics, vegetation indicators have been widely used in desertification assessment. In this study, rain use efficiency (RUE) derived from hyper-temporal remote sensing images has been used for desertification assessment. Based on time-series analysis, this study focused on how the desertification developed in Inner Mongolia and how the desertification reversed in the extremely arid environment. Results showed that during the past 11 years, there was no significant desertification development in Inner Mongolia. Parts of area showed a significant increase trend of RUE, especially in the eastern part of Ordos Plateau and southern Daqing Mountain, as well as the region from the Greater Hinggan Mountains to northern Yanshan Mountains. It is indicated that the ecological conditions in these areas have tended to be much better than before. The reason may be that the vegetation protection policies adopted in northern China have exerted a positive effect on the local environment. The results also showed that there was a significant relationship between rainfall and vegetation restoration, areas with more precipitation tend to be more easily restored, especially in the areas with more 300 mm precipitation. In addition, the research on desertification reversion showed that the desert edge region in western Inner Mongolia have changed intensively, and desertification reverse assessment needs to be further examined.
Cai F.,Institute of Atmospheric Environment |
Zhou G.S.,Chinese Academy of Meteorological Sciences |
Ming H.Q.,Liaoning Province Meteorological Service Center |
Li R.P.,Institute of Atmospheric Environment
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2013
Based on continuous observation data of 16 m gradient weather observation tower from 2006 to 2008 at Jinzhou agricultural ecosystem research station, dynamic characteristics of aerodynamic parameters roughness (z0) and zero-plane displacement(d) over a rainfed maize agroecosystem and their relationships with controlling factors during growing seasons are analyzed. The results showed that d appears about 10 days after jointing when plant height (h) is about 1.40 m and increases from 0.80-1.00 m to 1.00-1.40 m after tasseling stage. z0 is smaller than 0.20 m before tasseling stage and comes to the maximum about 0.4m before and after milk stage. d / h and z0 / h are 0.40-0.54 and 0.10-0.14, and are decreasing and increasing with LAI, respectively, before h comes to the maximum. Before d appears, negative exponent and positive linear relationships between z0 and wind speed at 2 m (u2), z0 and LAI or h are found. Yet, after d appears, relationship between u2 and z0 +d is more notable than those between u2 and z0 or d. At the same time, positive exponent relationships between z0 or d and LAI or h respectively are found. LAI and h influence more to z0 than to d and z0 +d with greater role for the latter. Those relationships are more conspicuous from d appearing to h coming to the maximum. These research conclusions will play an important reference role for setting up aerodynamic parameterization and improving land surface process model.
Li R.-P.,CAS Institute of Botany |
Li R.-P.,University of Chinese Academy of Sciences |
Li R.-P.,Institute of Atmospheric Environment |
Zhou G.-S.,CAS Institute of Botany |
Zhou G.-S.,Chinese Academy of Meteorological Sciences
PLoS ONE | Year: 2012
Plant phenology models, especially leafing models, play critical roles in evaluating the impact of climate change on the primary production of temperate plants. Existing models based on temperature alone could not accurately simulate plant leafing in arid and semi-arid regions. The objective of the present study was to test the suitability of the existing temperature-based leafing models in arid and semi-arid regions, and to develop a temperature-precipitation based leafing model (TP), based on the long-term (i.e., 12-27 years) ground leafing observation data and meteorological data in Northeast China. The better simulation of leafing for all the plant species in Northeast China was given by TP with the fixed starting date (TPn) than with the parameterized starting date (TPm), which gave the smallest average root mean square error (RMSE) of 4.21 days. Tree leafing models were validated with independent data, and the coefficient of determination (R 2) was greater than 0.60 in 75% of the estimates by TP and the spring warming model (SW) with the fixed starting date. The average RMSE of herb leafing simulated by TPn was 5.03 days, much lower than other models (&9.51 days), while the average R 2 of TPn and TPm were 0.68 and 0.57, respectively, much higher than the other models (<0.22). It indicates that TPn is a universal model and more suitable for simulating leafing of trees and herbs than the prior models. Furthermore, water is an important factor determining herb leafing in arid and semi-arid temperate regions. © 2012 Li, Zhou.