In this study, the diurnal and seasonal variations of CO2 fluxes in a subtropical mixed evergreen forest in Ningxiang of Hunan Province, part of the East Asian monsoon region, were quantified for the first time. The f...In this study, the diurnal and seasonal variations of CO2 fluxes in a subtropical mixed evergreen forest in Ningxiang of Hunan Province, part of the East Asian monsoon region, were quantified for the first time. The fluxes were based on eddy covariance measurements from a newly initiated flux tower. The relationship between the CO2 fluxes and climate factors was also analyzed. The results showed that the target ecosystem appeared to be a clear carbon sink in 2013, with integrated net ecosystem CO2exchange（NEE）, ecosystem respiration（RE）, and gross ecosystem productivity（GEP） of-428.8, 1534.8 and1963.6 g C m^-2yr^-1, respectively. The net carbon uptake（i.e. the-NEE）, RE and GEP showed obvious seasonal variability,and were lower in winter and under drought conditions and higher in the growing season. The minimum NEE occurred on12 June（-7.4 g C m^-2d^-1）, due mainly to strong radiation, adequate moisture, and moderate temperature; while a very low net CO2 uptake occurred in August（9 g C m^-2month^-1）, attributable to extreme summer drought. In addition, the NEE and GEP showed obvious diurnal variability that changed with the seasons. In winter, solar radiation and temperature were the main controlling factors for GEP, while the soil water content and vapor pressure deficit were the controlling factors in summer. Furthermore, the daytime NEE was mainly limited by the water-stress effect under dry and warm atmospheric conditions, rather than by the direct temperature-stress effect.展开更多
Qualitative and quantitative analyses of derivatized phenols in Beijing and in Xinglong were performed from 2016 to 2017 using gas chromatography-mass spectrometry.The results showed substantially more severe pollutio...Qualitative and quantitative analyses of derivatized phenols in Beijing and in Xinglong were performed from 2016 to 2017 using gas chromatography-mass spectrometry.The results showed substantially more severe pollution in Beijing.Of the 14 compounds detected,the total average concentration was 100 ng/m^3 in Beijing,compared with 11.6 ng/m^3 in Xinglong.More specifically,concentration of nitro-aromatic compounds(NACs)(81.9 ng/m^3 in Beijing and 8.49 ng/m^3 in Xinglong) was the highest,followed by aromatic acids(14.6 ng/m^3 in Beijing and 2.42 ng/m^3 in Xinglong) and aromatic aldehydes(3.62 ng/m^3 in Beijing and 0.681 ng/m^3 in Xinglong).In terms of seasonal variation,the highest concentrations were found for 4-nitrocatechol in winter in Beijing(79.1±63.9 ng/m^3) and 4-nitrophenol in winter in Xinglong(9.72±8.94 ng/m^3).The analysis also revealed diurnal variations across different seasons.Most compounds presented higher concentrations at night in winter because of the decreased boundary layer height and increased heating intensity.While some presented higher levels during the day,which attributed to the photo-oxidation process for summer and more biomass burning activities for autumn.Higher concentrations appeared in winter and autumn than in spring and summer,which resulted from more coal combustions and adverse meteorological conditions.The significant correlations among NACs indicated similar sources of pollution.Higher correlations presented within each subgroup than those between the subgroups.Good correlations between levoglucosan and nitrophenols,nitrocatechols,nitro salicylic acids,with correlation coefficients(r) of 0.66,0.69 and 0.69,respectively,indicating an important role of biomass burning among primary sources.展开更多
We present the diurnal and seasonal variability of ambient NH3, NO, NO2 and SO2 over Delhi, India. Ambient NH3, NO and NO2 were measured continuously during winter, summer and autumn seasons using NH3- and NOx-analyze...We present the diurnal and seasonal variability of ambient NH3, NO, NO2 and SO2 over Delhi, India. Ambient NH3, NO and NO2 were measured continuously during winter, summer and autumn seasons using NH3- and NOx-analyzer, which operates by chemiluminescence method with a higher estimation efficiency （〉 90%） than the chemical trap method （reproducibility 4.7%）. Prominent diurnal, day-to-day and seasonal variations of ambient mixing ratio of NH3, NO, NO2 and SO2 were observed during the study period. Seasonal variation with higher mixing ratio in winter was observed for all measured trace gases except NO. Day-night variation of all measured trace gases observed was higher in winter in comparison with summer. Late morning increase in NO2 mixing ratio might be attributed to conversion of NO to NO2 with the interaction ofO3.展开更多
Diurnal and seasonal variation of CO2 flux above the Korean Pine and broadleaved mixed forest in Changbai Mountain were expounded according to the measurements by eddy covariance technique. The results showed that the...Diurnal and seasonal variation of CO2 flux above the Korean Pine and broadleaved mixed forest in Changbai Mountain were expounded according to the measurements by eddy covariance technique. The results showed that the diurnal variation during growing season was closely correlated with photosynthetically active radiation （PAR）. The forest assimilated the CO2 in daytime and released in night. The maximum uptake occurred about 9 o’clock of local time in clear day. Assimilation was synchronous to PAR in cloudy day. The night respiration increased with increasing of shallow soil temperature. The CO2 flux also had obviously seasonal variation that was mainly controlled by temperature. Relationship between monthly net exchange of CO2 and monthly mean air temperature fit cubic equation. Remarkable uptake occurred in blooming growing season,May to August,and weak respiration occurred in dormant season,October to March,and relatively big release happed in October. Assimilation and respiration were nearly balanced during the transition of growing and dormant seasons. The annual carbon uptake of the ecosystem was-184 gC·m -2 .展开更多
The retrieved results in this paper by GMS-5/VISSR thermal infrared data with single time/dual channel Split-Window Algorithm reveal the characteristics of diurnal and seasonal variation of clear-sky land surface temp...The retrieved results in this paper by GMS-5/VISSR thermal infrared data with single time/dual channel Split-Window Algorithm reveal the characteristics of diurnal and seasonal variation of clear-sky land surface temperature （LST） of several representative land surface types in China, including Tarim Basin, QinghaiTibetan Plateau, Hunshandake Sands, North China Plain, and South China. The seasonal variation of clear-sky LST in above areas varies distinctly for the different surface albedo, soil water content, and the extent of influence by solar radiation. The monthly average diurnal ranges of LST have two peaks and two valleys in one year. The characteristics of LST in most land of East Asia and that of sea surface temperature （SST） in the south of Taiwan Strait and the Yellow Sea are also analyzed as comparison. Tarim Basin and Hunshandake Sands have not only considerable LST diurnal cycle but also remarkable seasonal variation. In 2000, the maximum monthly average diurnal ranges of LST in both areas are over 30 K, and the annual range in Hunshadake Sands reaches 58.50 K. Seasonal variation of LST in the Qinghai-Tibetan Plateau is less than those in East Asia, Tarim Basin, and Hunshandake Sands. However, the maximum diurnal range exists in this area. The yearly average diurnal range is 28.05 K in the Qinghai-Tibetan Plateau in 2000. The characteristics of diurnal, seasonal, and annual variation from 1998 to 2000 are also shown in this research. All the results will be valuable to the research of climate change, radiation balance, and estimation for the change of land surface types.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 41305066 and 91125016)the Special Funds for Public Welfare of China (Grant No. GYHY201306045)
文摘In this study, the diurnal and seasonal variations of CO2 fluxes in a subtropical mixed evergreen forest in Ningxiang of Hunan Province, part of the East Asian monsoon region, were quantified for the first time. The fluxes were based on eddy covariance measurements from a newly initiated flux tower. The relationship between the CO2 fluxes and climate factors was also analyzed. The results showed that the target ecosystem appeared to be a clear carbon sink in 2013, with integrated net ecosystem CO2exchange（NEE）, ecosystem respiration（RE）, and gross ecosystem productivity（GEP） of-428.8, 1534.8 and1963.6 g C m^-2yr^-1, respectively. The net carbon uptake（i.e. the-NEE）, RE and GEP showed obvious seasonal variability,and were lower in winter and under drought conditions and higher in the growing season. The minimum NEE occurred on12 June（-7.4 g C m^-2d^-1）, due mainly to strong radiation, adequate moisture, and moderate temperature; while a very low net CO2 uptake occurred in August（9 g C m^-2month^-1）, attributable to extreme summer drought. In addition, the NEE and GEP showed obvious diurnal variability that changed with the seasons. In winter, solar radiation and temperature were the main controlling factors for GEP, while the soil water content and vapor pressure deficit were the controlling factors in summer. Furthermore, the daytime NEE was mainly limited by the water-stress effect under dry and warm atmospheric conditions, rather than by the direct temperature-stress effect.
基金supported by the National Key R&D Program of China (No:2017YFC0210000)the Ministry of Science and Technology of China (No:2016YFC0202001).
文摘Qualitative and quantitative analyses of derivatized phenols in Beijing and in Xinglong were performed from 2016 to 2017 using gas chromatography-mass spectrometry.The results showed substantially more severe pollution in Beijing.Of the 14 compounds detected,the total average concentration was 100 ng/m^3 in Beijing,compared with 11.6 ng/m^3 in Xinglong.More specifically,concentration of nitro-aromatic compounds(NACs)(81.9 ng/m^3 in Beijing and 8.49 ng/m^3 in Xinglong) was the highest,followed by aromatic acids(14.6 ng/m^3 in Beijing and 2.42 ng/m^3 in Xinglong) and aromatic aldehydes(3.62 ng/m^3 in Beijing and 0.681 ng/m^3 in Xinglong).In terms of seasonal variation,the highest concentrations were found for 4-nitrocatechol in winter in Beijing(79.1±63.9 ng/m^3) and 4-nitrophenol in winter in Xinglong(9.72±8.94 ng/m^3).The analysis also revealed diurnal variations across different seasons.Most compounds presented higher concentrations at night in winter because of the decreased boundary layer height and increased heating intensity.While some presented higher levels during the day,which attributed to the photo-oxidation process for summer and more biomass burning activities for autumn.Higher concentrations appeared in winter and autumn than in spring and summer,which resulted from more coal combustions and adverse meteorological conditions.The significant correlations among NACs indicated similar sources of pollution.Higher correlations presented within each subgroup than those between the subgroups.Good correlations between levoglucosan and nitrophenols,nitrocatechols,nitro salicylic acids,with correlation coefficients(r) of 0.66,0.69 and 0.69,respectively,indicating an important role of biomass burning among primary sources.
基金the Department of Science and Technology,Government of India, New Delhi for financial support(Grant No. SR/S4/AS:12/2008)
文摘We present the diurnal and seasonal variability of ambient NH3, NO, NO2 and SO2 over Delhi, India. Ambient NH3, NO and NO2 were measured continuously during winter, summer and autumn seasons using NH3- and NOx-analyzer, which operates by chemiluminescence method with a higher estimation efficiency （〉 90%） than the chemical trap method （reproducibility 4.7%）. Prominent diurnal, day-to-day and seasonal variations of ambient mixing ratio of NH3, NO, NO2 and SO2 were observed during the study period. Seasonal variation with higher mixing ratio in winter was observed for all measured trace gases except NO. Day-night variation of all measured trace gases observed was higher in winter in comparison with summer. Late morning increase in NO2 mixing ratio might be attributed to conversion of NO to NO2 with the interaction ofO3.
文摘Diurnal and seasonal variation of CO2 flux above the Korean Pine and broadleaved mixed forest in Changbai Mountain were expounded according to the measurements by eddy covariance technique. The results showed that the diurnal variation during growing season was closely correlated with photosynthetically active radiation （PAR）. The forest assimilated the CO2 in daytime and released in night. The maximum uptake occurred about 9 o’clock of local time in clear day. Assimilation was synchronous to PAR in cloudy day. The night respiration increased with increasing of shallow soil temperature. The CO2 flux also had obviously seasonal variation that was mainly controlled by temperature. Relationship between monthly net exchange of CO2 and monthly mean air temperature fit cubic equation. Remarkable uptake occurred in blooming growing season,May to August,and weak respiration occurred in dormant season,October to March,and relatively big release happed in October. Assimilation and respiration were nearly balanced during the transition of growing and dormant seasons. The annual carbon uptake of the ecosystem was-184 gC·m -2 .
基金Supported jointly by the National Facilities and Information Infrastructure for Science and Technology Project (2005DKA31700) and the National Nature Science Foundation of China (Nos.40333034 and 49790020).
文摘The retrieved results in this paper by GMS-5/VISSR thermal infrared data with single time/dual channel Split-Window Algorithm reveal the characteristics of diurnal and seasonal variation of clear-sky land surface temperature （LST） of several representative land surface types in China, including Tarim Basin, QinghaiTibetan Plateau, Hunshandake Sands, North China Plain, and South China. The seasonal variation of clear-sky LST in above areas varies distinctly for the different surface albedo, soil water content, and the extent of influence by solar radiation. The monthly average diurnal ranges of LST have two peaks and two valleys in one year. The characteristics of LST in most land of East Asia and that of sea surface temperature （SST） in the south of Taiwan Strait and the Yellow Sea are also analyzed as comparison. Tarim Basin and Hunshandake Sands have not only considerable LST diurnal cycle but also remarkable seasonal variation. In 2000, the maximum monthly average diurnal ranges of LST in both areas are over 30 K, and the annual range in Hunshadake Sands reaches 58.50 K. Seasonal variation of LST in the Qinghai-Tibetan Plateau is less than those in East Asia, Tarim Basin, and Hunshandake Sands. However, the maximum diurnal range exists in this area. The yearly average diurnal range is 28.05 K in the Qinghai-Tibetan Plateau in 2000. The characteristics of diurnal, seasonal, and annual variation from 1998 to 2000 are also shown in this research. All the results will be valuable to the research of climate change, radiation balance, and estimation for the change of land surface types.
