The influence of observation environment on background noise level of gPhone gravimeter

Based on the observations of 36 gPhone gravimeters in 2015, the background noise levels in the seismic frequency band（200-600 s） and sub-seismic band（1-6 h） are calculated. The differences in the PSD（power spectrum density） of each band of gPhone gravimetric gauges in different surrounding environments were analyzed and compared with Peterson＇s NLNM（new low-noise model） which is derived from the envelope at the power spectrum density of 75 seismograph stations around the world. The results showed that： the influence of station type on the noise magnitude of gPhone gravimeter is very small; The seismic band noise magnitude（hereinafter referred to as SNM） and the sub-seismic band noise magnitude（hereinafter referred to as SSNM） in the coastal gPhone gravimeter are higher than those of inland stations. Although the local hydrological change has a great influence on the gravity observation, the rainfall is not directly relative to the noise magnitude of the instrument. Except 3 coastal stations, the eight stations which had the highest amplitudes in the SNM were located near the seismic belt. This indicates that the SNM of the gPhone Gravimeter may reflect some seismic information.Compared with the NLNM model, the PSD of the gPhone gravimeter is lower than the NLNM model in the long period band（〈3×10^（-5）Hz）, indicating that the gPhone gravimeter is more suitable for detecting long-period signals（〉10 h） than the seismometer.

Long-term variations of major atmospheric compositions observed at the background stations in three key areas of China

Atmospheric compositions and acid rain are closely related to atmospheric environment,weather,and climate change.In this study,the concentration levels and long-term trends of CO_(2),CH_(4),O_(3),PM_(2.5),PM_(10),and acid rain were presented at the Mt.Waliguan global baseline station in Qinghai,Shangdianzi and Lin'an regional background stations in the North China Plain(NCP)and the Yangtze River Delta region(YRD)of China based on the data observed until 2018.Significant increasing trends of CO_(2) were found at all of these stations.At Mt.Waliguan,the concentration levels and growth rate were consistent with the average values in the Northern Hemisphere(NH)and those observed at the Mauna Loa station in Hawaii.The CH_(4) also showed a upward tendency similar to that observed in NH.Compared with the observations at Mt.Waliguan global baseline station,the CO_(2) and CH_(4) mole fractions were higher at Shangdianzi and Lin'an regional background stations,indicating the important contributions of anthropogenic activities to the regional background level of CO_(2) and CH_(4).The annual averaged surface ozone showed increasing trends at Mt.Waliguan and Shangdianzi stations,whereas no clear trend was found at Lin'an station.Similar variations in the patterns of aerosol concentrations at Shangdianzi and Lin'an were found according to the PM_(2.5) or PM_(10) observations.Overall,the aerosol concentrations at both stations shown declining trends since the observations.However,two periods of high particle concentrations occurred in 2006-2007 and 2013-2014.The annual mean aerosol concentrations have continuously decreased after 2013-2014,indicating the effectiveness of pollution control in the NCP and YRD,especially since the implementation of the‘Action Plan for Prevention and Control of Air Pollution’in September 2013.Comparative analysis of aerosol with acid rain showed that the period with high concentrations of aerosols in the early years was consistent with that of severe acid rain pollution,suggesting that both aerosol pollution and severe acid rain are closely related to coal combustion emissions in China.As a result of the control of coal combustion emissions for acid and SO_(2),NO_(x) emissions have contributed more substantially to aerosols due to the rapid growth of vehicle ownership.A comparison of the trends of aerosols with the maximum daily 8-h average of surface ozone(MDA8)at Shangdianzi and Lin'an stations revealed the complicated relationship between aerosol reduction and ozone production,i.e.,together with the continuous improvement of particulate pollution in the NCP and YRD,the MDA8 at both stations showed a decreasing trend at first but subsequently increased after 2014 with aerosols remaining reduced.Such different variation patterns of the MDA8 with PM_(2.5)(or PM_(10))indicated the high challenge of synergic control of aerosol and ozone pollution in China.

OBSERVATION AND INVESTIGATION OF VARIABILITIES OF BASELINE CO_2 CONCENTRATION OVER WALIGUAN MOUNTAIN IN QINGHAI PROVINCE OF CHINA

In-situ measurement of atmospheric CO_2 was made at the top of the Waliguan Mountain(36°17′N,100°54′E,3816 m asl).where the air is not directly affected by the local anthropogenic and natural sources,by using a nondispersive infrared(NDIR)analyzer and following the procedures proposed by WMO.The CO_2 in the flask samples collected on the mountain was also analyzed in a laboratory.The measurements uncover the daily,monthly and seasonal variabilities and the baseline level of the CO_2 in the air over the“clean”area of Chinese hinterland.Results suggest that the CO_2 concentration over the East Asia continent has evident periodical variation,similar to that of global distribution.In 1992,an annual mean baseline CO_2 concentration of 356.4 ppm over the continent was obtained.The annual mean val- ue was 357.2 ppm for 1993.Some relationships between the CO_2 concentration at Waliguan and the weather conditions, especially,wind speed and direction are found through the observation.