Planet Boundary Layer sulfur dioxide (PBL-SO2) derived from Ozone Monitoring Instrument (OMI) are compared with
in-situ measurements from Differential Optical Absorption Spectroscopy (DOAS) and gas analyzer observations at three
sites in Beijing (Jan-Dec, 2007) and Hebei province (Jan-May, 2007). We use an Air Mass Factor (AMF) lookup table,
which was calculated via Linearized Discrete Ordinate Radiative Transfer (LIDORT) model, to convert OMI PBL-SO2
slant column density to vertical column density. Co-locate Lidar (UV) aerosol extinction profiles are used to correct the
effect of aerosol. Results show that, AMF decreases less than 3% with the increasing solar zenith angle from 0° to 45°,
AMF is more sensitive to surface albedo and the viewing zenith angle. AMF reduces by 6% with the increasing Ozone density from 275DU to 325DU. Normally, absorption aerosol reduces AMF and scattering aerosol increases AMF, aerosol profiles are critical to AMF estimation. Under very clear conditions, from winter to later spring, OMI observed SO2 values are underestimated by 3.6ppbv to 20ppbv, but in reasonable agreement with in-situ measurements. Because
of the effects of Sub-pixel cloud contamination, long slant path (higher solar zenith angles or viewing zenith angles),
differences in aerosol types and large Aerosol Optical Depth (AOD), direct comparisons between the OMI retrieval and
the in situ measurements show that the correlation is low and the differences vary with months, while averaging over half
a month can significantly reduces the bias.
Ground-based measurements of land surface temperature as measured by Platinum resistance thermometer partly buried in the soil surface radiation temperature measured by infrared thermometer and near surface air temperature measurements at Gaize (32.30°N 84.06°E 4420 m) on the western Tibetan Plateau from January 2001 to December 2003 were compared with Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) products (Version 4) produced by the generalized split-window (MOD11A1) and the day/night LST algorithm (MOD11B1). A comparison of LSTs shows that the LSTs produced by the day/night LST algorithm agree quite well with ground-based surface temperature and surface radiation temperature measurements with a mean difference of zero and root mean square errors being less than 1 K. MODIS LST retrieved by the day/night LST algorithm is found to be 2.2 K less than the air temperature at 0. 5 m above the surface. Compared to that produced by the day/night LST algorithm the LST produced by the generalized spit-window LST algorithm is underestimated by 1.9 K.
Measurements of CO and H20 total content in the atmosphere by using ground-based solar spectroscopic system were conducted in Beijing since 1992. Measurements have been done every year during time period of late autumn and early winter when the heating activities started in the most places of Northern China. So the impact of human activities on CO variation can be assessed based on the obtained results. Brief description of the used spectroscopic method is introduced. Some variation characteristics of CO and H2O total content in the atmosphere over Beijing the background value of CO content in Beijing area and variation trend of CO and H20 content in the last 8 years are given and discussed in this paper. Results show evident daily and seasonal variations of CO and H2O content and heating activities in Northern China have a remarkable influence on CO content in the atmosphere. On average CO total content in the atmosphere over Beijing area maintains a high level (about 0.130-0.150 atm-cm) all along and no clear annual variation tendency of CO column content was observed since 1996 in Beijing area.
The quasi-continuous measurements of direct solar and sky scattered spectrum over Beijing have been conducted since September 1998 with an automatic moderate resolution solar spectroradiometer (MORSAS) developed by the Institute of Atmospheric Physics, Chinese Academy of Sciences. The measurements of direct solar spectrum under cloud free conditions, including clear and turbid skies, were used to derive atmospheric aerosol optical thickness. During the period of Asian-Pacific Regional Aerosol Characterization Experiment (ACE-Asia) in spring 2001, a spectral radiometer CIMEL CE-318 in AERONET (owned by US NASA/GSFC) was operated at the same time and the same place with MORSAS. Comparing the observed results from the two instruments, they are consistent with each other. In this paper we present the variation of atmospheric aerosol optical thickness and Angstrom exponent which symbolizes the width of particle spectrum in Beijing during recent three years. In contrast with the middle of 1990’s, the atmospheric aerosol optical thickness in autumn and winter in recent years decreased slightly, indicating that Beijing air quality has been improved by certain local environmental management, whereas in spring in the latest 2 years the atmospheric aerosol optical thickness has evidently increased as the increase of the dust weather events, and the Angstrom exponent tends to be lower. This reveals that the ratio of larger particles especially the large dust-sand particles in the air has increased. So it is very important to enhance dust source management for those upstream and local arid and semi-arid regions.
Conference Committee Involvement (1)
Ultraviolet Ground- and Space-based Measurements, Models, and Effects II
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