Aerosol activity of forming cloud droplets affects cloud micro-physics and indicates aerosol hygroscopicity. Application of the cloud condensation nuclei (CCN) counter (CCNC) is an important method for studying CCN-active particles. Factors impacting measurements using CCNC are analyzed by laboratory study. In CCNC, variations of supre-saturations (SS) are found to be proportional to variations of the pressure and the flow-rate. Temperature conditions, under which CCNC is working, exhibit nonlinear influnces on SSs in CCNC. Varying aerosol losses with particle size due to the pressure adjustment is found when differential pressure is higher than 300 hPa. Underestimation of CCN number concentration is found when particle number concentration is higher than 10000/cm³ and SS in CCNC is lower than 0.2%. This is because only part of CCN-active particles can activate due to the vapor depletion in CCNC. The results and suggestions provide instructions for CCN measurment and would help improving quality control and analysis of CCN data.

In order to study the diurnal variations of aerosol hygroscopic properties in North China, a new humidified nephelometer system is designed with the advantage of high time resolution and high humidification efficiency. In this system, two water baths are used for the first time to control humidification process in turn, reducing the circulation cycle from two to three hours to about one hour. Besides the nephelometer lamp power is reduced from 75 W to 25 W, and a piece of heat mirror is set ahead of the lamp. After those modifications, the temperature rising inside the chamber decreases from 4.3 ºC to 2.3 ºC and humidification efficiency rises. The original RH sensor inside the chamber is inaccurate, so two Vaisala sensors are set at the inlet and outlet of the nephelometer to correct the RH inside the chamber. In the future, this humidified nephelometer system will be used in in situ measurement in North China to get the diurnal variation properties of aerosol light scattering enhancement factor.

Longtime in-situ measurements of total ozone from the ground-based Brewer observatories at Longfengshan in Heilongjiang Province and Waliguan in Qinghai Province were analyzed together with the according geopotential height data from NCEP R1 reanalysis series. Abnormal day-to-day fluctuations in the total ozone amount were found at times, which were analyzed in respect to synoptic processes. Results show that the impact of synoptic conditions is highly related to the variation of the total ozone amount. The anomaly in total ozone amount mostly appears in winter and spring (from November to May in the following year). The abnormal high total ozone amounts (the first kind of abnormal data points) always occur when the station is at the rear of the near surface (1000 hPa) cyclone with a simultaneous air pressure trough approaching in lower stratosphere (250 to 70 hPa). The abnormal low total ozone amounts (the second kind of abnormal points) always occur when the station is behind a near surface anticyclone with a simultaneous air pressure ridges approaching in lower stratosphere. The anomaly in total ozone amount can be considered as a signal for the upcoming transition between near surface cyclone and anticyclone.

The three-dimensional water vapor field is obtained using Monte Carlo tomography algorithm based on the small-scale network of ground-based GPS. After the proof of the accuracy of the tomography water vapor field through the comparison between the profiles from the radiosonde and tomography field, the three-dimensional water vapor field and the data of Weather Radar are used to study the variation of the water vapor in the strong convection and heavy precipitation processes which took place on July 29, 2011. For the first time, the authors propose the continuous change and fine structure of the small-scale water vapor field during the convective processes. For local convection process, the tomography vapor field can capture the water vapor enrichment phenomenon and provide its location 20 minutes ahead the precipitation and it is an indication to the precipitation forecast. For rainstorm process, the water vapor field can explicitly show the position and intensity of the vapor transport source which meet well with the conclusion from the analysis of weather radar and meteorological situation.

The data of the network of 13 GPS are used to perform the sensitivity tests for the important parameters of the Monte Carlo tomography algorithm such as the average distance of the GPS stations, tomography temporal resolution and Monte Carlo random times. The accuracy of tomography rises with the decrease of the average station distance and the increase of the random times. However the decrease of the temporal resolution of the tomography does not help much to the accuracy of the tomography. A new way is also proposed to obtain the final tomography field. The final tomography field is obtained by averaging “sub-optimal” tomography fields instead of the one “optimal”, and it is proved to reduce the error by around 30%.

A modified method for calibrating the supersaturations in the chambers of DMT Cloud Condensation Nuclei Counter is introduced, which decreases the uncertainty in the results of the calibration. In the new method, the complete size-resolved activation ratio for ammonium sulfate is observed, and the activation critical diameter is yielded via fitting the size-resolved activation ratio with two Gauss error functions. With the new method, users can do the calibration periodically to guarantee high-quality observations.

Radiosonde (RS) data over Beijing in 2008 was employed to analyze vertical distributions of water vapor in this area. A parameterization scheme of water vapor profiles is proposed according to different conditions of Planetary Boundary Layer (PBL). In the condition of Stable Boundary Layer (SBL) or shallow boundary layer, the parameterization scheme of water vapor profiles can be formulated by q=q₀e^z/2624, here q₀ is specific humidity at surface. In the condition of Convective Boundary Layer (CBL), the vertical distribution of water vapor is significantly influenced by CBL. The parameterization scheme of water vapor profiles can be expressed as 1) within the CBL (0≤ z0; 2) near the top of CBL (|z-PBL|<200), q=q₀(A-B(z-PBL)); 3) above the CBL (PBL+200≤z), q=Cq₀(z-5000-PBL), here z is height (unit is metre), PBL is the height of PBL (unit is metre). A=0.72, B=1.4×10^-3m^-1, C=?9.17×10^?5m^-1. For CBL, the IWV would be underestimated by 10% using the exponential distribution. A better estimation is achieved with this parameterization scheme proposed.

Ground-level NO₂ concentrations in Shanghai between May 2006 and August 2008 are estimated using the tropospheric NO₂ column concentration data of Ozone Monitoring Instrument (OMI) onboard AURA. In-situ measurements of surface NO₂ concentrations of Xujiahui, Shanghai are corrected using global 3-D chemical transport model MOZART-2, and are used to validate the surface NO₂ concentrations derived from tropospheric columns. The results show a significant correlation between monthly mean OMI derived surface NO₂ concentrations and in-situ NO₂ surface concentrations (R²=0.88), indicating that it is reliable to infer ground-level NO₂ concentration from NO₂ tropospheric column concentration.

The study of general status of NMOCs, NMOCs composition and ozone formation potentials of various NMOCs species help better understand the ozone problem and make effective ozone abatement strategies in NMOCs-sensitive regime. Analysis of NMOCs 24-hours sampling from November 6, 2005 to August 8,2007 in urban Shanghai Xujiahui indicates that daily NMOCs display no apparent seasonal variation with average concentration of about 50 ppbv. The major components are alkanes, alkenes and aromatics. Due to their relatively high reactivities and concentrations, aromatics play a dominant role in contributing to ozone photochemical production. Toluene, xylene, ethylbenzene, butene and propene are found to be among the top list of ozone formation potentials. NMOCs in urban Shanghai are largely of anthropogenic origin. They are mainly from vehicular exhausts, evaporation of solvents and architectural materials and emissions from the petrochemical complex in the southern Jinshan District.

Based on a daily precipitation dataset of 521 meteorological stations in China, trends of regional average precipitation amounts, precipitation days and daily precipitation intensities of the 9 different precipitation classes, rangingfrom 0.1-4.9 ,5-9.9 , 10- 16. 9 ,17-24. 9 ,25-37.9 ,38- 49. 9 ,50-74. 9 ,75-99.9 mmto over 100 mm, were studied for the period of 1961-2000. The results revealed that,the trends of the lightest precipitation amounts were caused bythe changes of precipitation days, while the changes of the heaviest precipitation amounts were mainly dominated by the precipitation intensity. The analysis on precipitation frequency and the proportion of precipitation amount of each precipitation class showed that, in spite of the decreasing trend in North China and Sichuan Basin, the precipitation frequencies andthe proportions of precipitation amounts in other regions went upward significantly, indicating an increasing contribution of the heavier precipitation to the total precipitation amount.

Spatial distributions of tropospheric NO₂ over China and variations of tropospheric NO₂ for selected regions in China are studied using of satellite monitoring data (GOME and SCIAMACHY) from March 1996 to March 2008. Global Chemistry-Transport Model (MOART-2) simulation is carried out to reveal significant seasonal variations of tropospheric NO₂ over megalopolis areas in eastern China. Results show that: 1) Maximum distribution of tropospheric NO₂ lies in region of Beijing-Hebei-Tianjing, Yangtze Delta, Perl river delta. Obvious increasing trend can be seen over East China, with a yearly increasing rate of 0.9×1015cm_-2. 2) Becacuse of effective eliminating of NO₂ by OH, tropospheric NO₂ over megalopolis in East China shows significant seasonal variations: tropospheric NO₂ maximum appears in winter, and decreases sharply in summer. In background area West China where natural emissions dominates, tropospheric NO₂ shows reversed phenomenon compared to the East.