[Observation Analyses of Aerosol Size Distribution Properties from February to March, 2019 in Tianjin Urban Area].

The aerosol size distribution is an important physical parameter reflecting the source, formation process, and pollution characteristics of aerosol particles. In order to study the properties of aerosol number concentration and size distributions in the Tianjin urban area,the aerosol number concentration and size distributions ranging from 10-600 nm were detected using a scanning mobility particle sizer (SMPS) during February and March, 2019. The results showed that in the Tianjin urban area, the aerosol number concentration,surface area concentration.

[Characteristics of BTEX and Health Risk Assessment During Typical Pollution Episodes in Summer and Winter in Tianjin Urban Area].

Real-time BTEX(including benzene, toluene, ethylbenzene, -, -, and -xylenes) were measured continuously in Tianjin urban site in July 2019 and January 2020 using a Syntech Spectras GC955 analyzer. The BTEX concentration levels, composition, and evolutionary mechanisms during typical pollution episodes were investigated. The potential sources of BTEX were analyzed qualitatively using the diagnostic ratios method.

Evaluation and improvement study of the Planetary Boundary-Layer schemes during a high PM episode in a core city of BTH region, China.

Accurate depictions of planetary boundary layer (PBL) processes are important for both meteorological and air quality simulations. This study examines the sensitivity of the model performance of the Weather Research Forecasting model coupled with Chemistry (WRF-Chem) to five different PBL schemes and further to different turbulence parameters for the simulation of a winter haze episode in Tianjin, a core city of the Beijing-Tianjin-Hebei (BTH) region in China. To provide a direct and comprehensive evaluation of the PBL schemes, measurements from multiple instruments are employed, including both meteorological and air quality quantities from near-surface observations, vertical sounding measurements and ceilometer data.

Seasonal variation and secondary formation of size-segregated aerosol water-soluble inorganic ions in a coast megacity of North China Plain.

The aerosol samples of water-soluble inorganic ions (WSIs), including SO, NO, NH, Cl, K, Na, Ca, and Mg in size-segregated particulate matter (PM), were collected by an Anderson sampler (with 8 nominal cut-sizes ranged from 0.43 to 9.0 μm) in urban Tianjin during 2013-2014.

Comparison on aerosol physicochemical properties of sea and land along the coast of Bohai, China.

The Bohai Sea is one of four major sea areas adjacent to China, air pollution is becoming an issue along the Bohai coast owing to rapid industrialization and urbanization. To analyze the sea-land interaction and its influence on regional particulate pollution, a comparison of sea and land aerosol physicochemical properties was carried out using observations and numerical simulation. Three observation sites, an ocean site on the Bohai Sea, a coastal station in the Tanggu district, and an inland station in Tianjin City were established.

[Transport Characteristics of PAN and O in the Lower Atmosphere of the Boundary Layer in Tianjin in Summer].

The volume concentration of peroxyacetyl nitrate (PAN) and O in the atmosphere were measured at the Tianjin Meteorological Tower in summer 2017 by using the online instrument with meteorological parameters and back trajectory analysis to analyze the delivery characteristics of PAN and O. The average volume concentrations of PAN and O during the observational period are (0.73±0.

[Construction and Application of Vertical Diffusion Index for Analyzing Weather During Pollution Events in Tianjin].

Based on temperature and wind speed data from the 255 meter tall meteorological tower, the characteristics of atmospheric stability were analyzed in Tianjin, with the vertical diffusion index and constructed by atmospheric chemical models. This provided information to use the vertical dispersion analysis method to forecast pollution from weather data. The results show that the comprehensive use of atmospheric stability and the vertical diffusion index can provide a better pollution forecast.

[Characteristics of the Size Distribution of Water-soluble Ions During a Heavy Pollution Episode in the Winter in Tianjin].

To characterize the size distribution of water-soluble inorganic ions (WSⅡ) during a heavy pollution episode, particle samples were collected by an Andersen cascade sampler in Tianjin in January 2014, and the concentrations of eight WSⅡ (Na, NH, K, Mg, Ca, Cl, NO, and SO) during a typical haze episode were analyzed by ion chromatography. The sources and formation mechanisms of WSⅡ were analyzed based on their size distributions. The results showed that the daily average concentrations of PM and PM were (138±100) μg·m and (227±142) μg·m, respectively, and the average concentration of total WSⅡ concentrations (TWSⅡ) in the coarse and fine particles were (34.

Vertical observation and analysis on rapid formation and evolutionary mechanisms of a prolonged haze episode over central-eastern China.

To clarify the rapid formation and evolutionary mechanisms of an extremely severe and persistent haze and fog (HF) episode that occurred in central-eastern China from Dec 20 to 25, 2015, a novel campaign was conducted and vertical profiles of wind, temperature, light extinction coefficient (LEC) and PM concentration were used to analyze the rapid formation and evolutionary mechanisms of this HF episode. The substantial downward transportation of regional pollution from high layers and stagnant weather conditions favorable for the local pollution accumulation were the two main causes of the rapid increase in pollutant concentration. Southwest wind speeds of 4m/s between 300 and 600m and obvious downward flows were observed, whereas the southwest wind speeds were low below 300m, and strong temperature inversion with intensity of 4.

Vertical characteristics of PM2.5 during the heating season in Tianjin, China.

In this study, PM2.5 samples were collected at four heights (10m, 40m, 120m and 220m) at a meteorological tower in the daytime and nighttime during the heating season in Tianjin, China. The vertical variation and diurnal variability of the concentrations of PM2.

"All air-plasma" terahertz spectroscopy.

We demonstrate terahertz wave generation and detection capabilities up to 6 THz without the need for solid state materials, biased electrodes, or forward propagating signal collection. An "all air-plasma" terahertz system is used to encode explosive material resonant signatures into the 357 nm nitrogen fluorescence line of a bichromatic field-induced laser plasma filament. These results show the practicability to extend these measurements to remote locations where terahertz pulse information is no longer limited by water vapor absorption, phonon resonance, or signal collection directionality.

Enhancement of photoacoustic emission through terahertz-field-driven electron motions.

We report the study of enhanced photoacoustic emission from a laser-induced plasma under the influence of the terahertz field up to 100 kV/cm. We theoretically and experimentally investigate the energy transfer from terahertz radiation to molecular translational motion, through terahertz-field-driven electron motion and inelastic electron-molecule collision. The enhanced photoacoustic emission in the frequency range of 1-140 kHz is quadratically dependent on the incident terahertz field.

Laser-induced photoacoustics influenced by single-cycle terahertz radiation.

Laser-induced plasma acoustic waves are enhanced under the illumination of single-cycle terahertz (THz) radiation, making THz-enhanced acoustics (TEA) a useful method for THz wave detection. During a single-cycle THz pulse with its peak field of 100 kV/cm, a pressure enhancement of 10% is observed throughout the acoustic spectrum up to 140 kHz, and the TEA signal is found to increase linearly with THz wave intensity. By using dual-color laser excitation to manipulate free electron drift, it is possible to modulate the enhanced acoustic signal and recover a coherent THz time-domain waveform by simply "listening" to the plasma.

Terahertz-radiation-enhanced emission of fluorescence from gas plasma.

We report the study of femtosecond laser-induced air plasma fluorescence under the illumination of terahertz (THz) pulses. Semiclassical modeling and experimental verification indicate that time-resolved THz radiation-enhanced emission of fluorescence is dominated by the electron kinetics and the electron-impact excitation of gas molecules or ions. We demonstrate that the temporal waveform of the THz field could be retrieved from the transient enhanced fluorescence, making omnidirectional, coherent detection available for THz time-domain spectroscopy.