Zhang Ts

Haze observations by simultaneous lidar and WPS in Beijing before and during APEC, 2014

We present combined Mie lidar, ozone lidar and wide-range particle spectrometer observations which were carried out in Beijing, north China during two periods—one haze period before the Asia-Pacific Economic Cooperation (APEC) meeting and one moderate pollution period during the meeting in 2014. High extinction coefficient, moderate ozone concentration and variable particle number concentration were obtained throughout the first haze observation period. The mean extinction coefficients in the two pollution periods were 0.52 and 0.23 km-1, respectively, at 532 nm. The ozone concentration during the first haze phase was more various with a higher average value of 49 ppb compared with that in the second pollution observations (32 ppb). Compared with the same metrological condition occurring at the end of October, the sharply decreased aerosol extinction coefficient and ozone concentration show the effectiveness of the emission-cutting measures implemented during APEC in November. The comparison of aerosols and ozone in different heights indicate different pollution sources and the complicated ozone process of generation and disappearance. The correlation between the scattering coefficient and particle number concentrations of various diameter depended on the ambient humidity. Especially the particle number concentration (500 nm–1 µm) contributed most to PM2.5 concentration. The four-day back trajectories from a Hybrid Single-particle Lagrangian Integrated Trajectory (HYSPLIT) model indicate that the air masses in the lower boundary layer before and during APEC were advected from the densely populated south regions of China and the long pollution transportation passing through northern China.

Characterization of ozone in the lower troposphere during the 2016 G20 conference in Hangzhou

Recently, atmospheric ozone pollution has demonstrated an aggravating tendency in China. To date, most research about atmospheric ozone has been confined near the surface, and an understanding of the vertical ozone structure is limited. During the 2016 G20 conference, strict emission control measures were implemented in Hangzhou, a megacity in the Yangtze River Delta, and its surrounding regions. Here, we monitored the vertical profiles of ozone concentration and aerosol extinction coefficients in the lower troposphere using an ozone lidar, in addition to the vertical column densities (VCDs) of ozone and its precursors in the troposphere through satellite-based remote sensing. The ozone concentrations reached a peak near the top of the boundary layer. During the control period, the aerosol extinction coefficients in the lower lidar layer decreased significantly; however, the ozone concentration fluctuated frequently with two pollution episodes and one clean episode. The sensitivity of ozone production was mostly within VOC-limited or transition regimes, but entered a NOx-limited regime due to a substantial decline of NOx during the clean episode. Temporary measures took no immediate effect on ozone pollution in the boundary layer; instead, meteorological conditions like air mass sources and solar radiation intensities dominated the variations in the ozone concentration.

A synchronous observation of enhanced aerosol and NO2 over Beijing, China, in winter 2015.

Despite extensive efforts into the characterization of air pollution during the past decade, concurrent real-time characterization of aerosol and NO2 as well as satellite observation above the urban canopy in the megacity of Beijing has sparsely been performed to date. We conducted a simultaneous real-time measurement of aerosol and NO2 in urban Beijing in a pollution episode from November 25, 2015 to December 2, 2015. The aerosol extinction coefficient was measured by a 532 Mie lidar and the NO2 concentration by a Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS). The highest aerosol extinction coefficient was 1.55 (±0.16) km-1 at 532m at a height of 0.27km. The high average aerosol extinction was observed throughout the pollution period, probably due to the favorable static weather conditions under high surface high-pressure system and transportation sources. NO2 showed similar temporal variations between ground level and 0.3km, whereas a much weaker diurnal evolution was found for NO2. The boundary layer structures were observed, and the relatively homogeneous mixture maintained the pollution within the layer under 0.5km. Ozone Monitoring Instrument (OMI) NO2 products based on well-known DOAS trace gas fitting algorithm and WRF-Chem model further illustrated the simultaneous enhancement of NO2 during the observation period. Backward trajectories suggest that long-range pollution transportation from northwest China contributes more to this pollution event.

Scanning vertical distributions of typical aerosols along the Yangtze River using elastic lidar

In recent years, China has experienced heavy air pollution, especially haze caused by particulate matter (PM). The compositions, horizontal distributions, transport, and chemical formation mechanisms of PM and its precursors have been widely investigated in China based on near-ground measurements. However, the understanding of the distributions and physical and chemical processes of PM in the vertical direction remains limited. In this study, an elastic lidar was employed to investigate the vertical profiles of aerosols along the Yangtze River during the Yangtze River Campaign of winter 2015. Some typical aerosols were identified and some events were analyzed in three cases. Dust aerosols can be transported from the Gobi Desert to the Yangtze River basin across a long distance at both low and high altitudes in early December. The transport route was perpendicular to the ship track, suggesting that the dust aerosols may have affected a large area. Moreover, during transport, some dust was also affected by the areas below its transport route since some anthropogenic pollutants were mixed with the dust and changed some of its optical properties. Biomass-burning aerosols covering a distant range along the Yangtze River were identified. This result directly shows the impact areas of biomass-burning aerosols in some agricultural fields. Some directly emitted aerosol plumes were observed, and direct effects of such plumes were limited both temporally and spatially. In addition, an aerosol plume with very low linear depolarization ratios, probably formed through secondary processes, was also observed. These results can help us better understand aerosols in large spatial scales in China and can be useful to regional haze studies.

Regional Air Pollution Distribution and Transportation Monitoring by Spectroscopic Remote Sensing

The regional air pollution distribution and transportation monitoring system was develpoed by spectroscopic remote sensing techniques. With the demonstration, spectroscopic techniques were proved to be critical in regional air quality monitoring.

Observations of Atmospheric Haze in Central China Region (CCR) by an elastic-polarized Lidar

A field campaign of atmospheric haze was conducted in Central China Region (CCR) in winter 2013. LIDAR provided spatial-temporal optical properties of aerosols. Metrological condition and back trajectories were used to identify the pollutant source.

The design and study of a new micropulse Lidar

Micro pulse lidar(MPL) is an effective tool for atmospheric aerosol and cloud detecting. In order to make the structure of the micro pulse lidar more compact, solve the problem that it always very difficult to adjust the transmitting and receiving optical paths to parallel in the traditional system, avoid the influence of the geometric overlap factor and reduce the complexity of the data processing, Anhui institute of optics and fine mechanics of the Chinese academy of sciences designs a new type of micro pulse lidar, particularly designs the followed up optical unit of the micro pulse lidar. A combination of emitting and receiving fibers in a signal bundle changes the structure of the subsequent optical unit in the traditional system to make the transmitting and receiving optical paths coaxial. The public end of the Y type optical fiber bundle is composed of a transmitting optical fiber in the center and eight receiving optical fibers in the periphery. After a brief introduction of the new system, the key parameters of the new micro pulse lidar system and the Y type optical fiber bundle were described in some detail. In order to verify the feasibility of the new structure of the micro pulse lidar system, a continuous observation experiment was carried out in Hefei area to detect the horizontal distribution of the atmospheric aerosol and pollutions. The data measured in the experiment in the November 2013 was processed with Fernald method and the profile of the atmospheric aerosol horizontal extinction coefficient distribution was inverted. The data inversion results showed that: the data acquired by the new lidar system and the extinction coefficient distribution inverted by Fernald algorithm are all very reasonable, and the time-space distribution of atmospheric aerosols extinction coefficient can reflect the distribution of the atmospheric aerosol and pollutions near the ground effectively. All of the experiment results indicate that the design of the new micro pulse lidar system is effective.