As improved and accumulated satellite records become available,it is significant to provide up-to-date perspectives on the spatiotemporal signatures of tropospheric nitrogen dioxide(NO2)over China,the knowledge of which is helpful for air pollution control.In this study,the Ozone Monitoring Instrument NO2 dataset for the last 10 years(2005–14)was retrieved to examine multiple aspects of NO2 columns,including distributions,trends,and seasonal cycle.The pattern of average NO2suggests five hotspots with column density higher than 20×1015 molec cm-2:Jing-Jin-Tang;combined southern Hebei and northern Henan;Jinan;the Yangtze River Delta;and the Pearl River Delta.Furthermore,substantial and widespread NO2 growths are distributed over the North China Plain.By contrast,downward trends in NO2 amounts prevail in the megacities of Beijing,Shanghai,and Guangzhou,despite generally high loading levels.Except for the Pearl River Delta,there appears to be temporally consistent behaviors across all regions considered,where NO2 had an abrupt decline during 2008 to 2009,then a drastic increase up to 2013,before beginning to reduce again after 2013.However,the NO2 over the Pearl River Delta is not coevolving with the rest,having experienced a moderate rise from 2005 to 2007,followed by a reduction thereafter.A marked seasonality is apparent,with a maximum in winter and a minimum in summer,regardless of the region.The annual amplitude of NO2 is less pronounced over the Pearl River Delta,whereas the largest range is observed over the combined Southern Hebei and Northern Henan region,induced by enhanced NO2emission in wintertime due to intense domestic heating.
WANG TingWANG Pu-CaiFrancois HENDRICKYU HuanMichel VAN ROOZENDAEL
Measurements of aerosol optical characteris- tics were carried out with a Photoelectric Aerosol Nephelometer （PhAN） in Beijing and at Xinglong Obser- vatory, which is located 150 km northeast of Beijing. Aerosol size distributions were retrieved by means of the inverse problem solution. Mean volume size distributions of the fine aerosol fraction were unimodal with the maximum radius in the range 0.11-0.15 pm. Accumula- tion of aerosol matter in the air basin of Beijing takes place mainly due to the growth of particle size, but not their number. A simple optical method to detect aerosol nonsphericity is proposed.
Based on the optimal estimation method, a satellite XCO2 retrieval algorithm was constructed by combining LBLRTM with VLIDORT. One-year GOSAT/TANSO observations over four TCCON stations were tested by our algorithm, and retrieval results were compared with GOSAT L2 B products and ground-based FTS measurements. Meanwhile, the influence of CO2 line mixing effect on retrieval was estimated, and the research showed that neglecting CO2 line mixing effect could result in approximately 0.25% XCO2 underestimation. The accuracy of XCO2 retrievals was similar to GOSAT L2 B products at cloud-free footprints with aerosol optical depth less than 0.3, and 1% accuracy of XCO2 retrievals can be reached based on the validation result with TCCON measurements.
The North China Plain(NCP) has recently faced serious air quality problems as a result of enhanced gas pollutant emissions due to the process of urbanization and rapid economic growth.To explore regional air pollution in the NCP,measurements of surface ozone(O3),nitrogen oxides(NOx),and sulfur dioxide(SO2) were carried out from May to November 2013 at a rural site(Xianghe) between the twin megacities of Beijing and Tianjin.The highest hourly ozone average was close to 240 ppbv in May,followed by around 160 ppbv in June and July.High ozone episodes were more notable than in 2005 and were mainly associated with air parcels from the city cluster in the hinterland of the polluted NCP to the southwest of the site.For NOx,an important ozone precursor,the concentrations ranged from several ppbv to nearly 180 ppbv in the summer and over 400 ppbv in the fall.The occurrence of high NOx concentrations under calm conditions indicated that local emissions were dominant in Xianghe.The double-peak diurnal pattern found in NOxconcentrations and NO/NOx ratios was probably shaped by local emissions,photochemical removal,and dilution resulting from diurnal variations of surface wind speed and the boundary layer height.A pronounced SO2 daytime peak was noted and attributed to downward mixing from an SO2-rich layer above,while the SO2-polluted air mass transported from possible emission sources,which differed between the non-heating(September and October) and heating(November) periods,was thought to be responsible for night-time high concentrations.
The anthropogenic CO column content in the atmosphere is derived from measurements with infrared grating spectrometers in Beijing,China,and Moscow,Russia,during 1992–2012.Some specific variation characteristics and long-term variation trends of the CO column content in the atmosphere in these regions are discussed.An evident variation trend of anthropogenic CO in the atmosphere for the Beijing region is not observed during 1992–2012,while for the Moscow region,it decreases yearly by about 1.4% for the same period.High CO concentrations appear quite frequently in Beijing,but much less frequently in Moscow,except during the natural fire events in summer 2010.From back trajectory analysis,the high CO concentration observed in Beijing can be attributed to the intensive CO emission sources in its surrounding areas.
WANG Pu-CaiGeorgy S.GOLITSYNWANG Geng-ChenEvgeny I.GRECHKOVadim S.RAKITINEkaterina V.FOKEEVAAnatoly V.DZHOLA
Total Cloud Cover （TCC） over China deter- mined from four climate datasets including the Interna- tional Satellite Cloud Climatology Project （ISCCP）, the 40-year Re-Analysis Project of the European Centre for Medium-Range Weather Forecasts （ERA-40）, Climate Research Unit Time Series 3.0 （CRU3）, and ground sta- tion datasets are used to show spatial and temporal varia- tion of TCC and their differences. It is demonstrated that the four datasets show similar spatial pattern and seasonal variation. The maximum value is derived from ISCCE TCC value in North China derived from ERA-40 is 50% larger than that from the station dataset; however, the value is 50% less than that in South China. The annual TCC of ISCCP, ERA-40, and ground station datasets shows a decreasing trend during 1984-2002; however, an increasing trend is derived from CRU3. The results of this study imply remarkable differences of TCC derived from surface and satellite observations as well as model simu- lations. The potential effects of these differences on cloud climatology and associated climatic issues should be carefully considered.
