A new approach to quantifying vehicle induced turbulence for complex traffic scenarios

Traffic-related pollutants adversely affect air quality, especially in regions near major roadways. The vehicleinduced turbulence(VIT) is a significant factor that controls the initial dilution, dispersion, and ultimately the chemical and physical fate of pollutants by altering the conditions in the microenvironment. This study used a computational fluid dynamics(CFD) software FLUENT to model the vehicle-induced turbulence(VIT) generated on roadways, with a focus on impact of vehicle-vehicle interactions, traffic density and vehicle composition on turbulent kinetic energy(TKE). We show, for the first time, that the overall TKE from multiple vehicles traveling in series can be estimated by superimposing the TKE of each vehicle, without considering the distance between them while the distance is greater than one vehicle length. This finding is particularly significant since it enables a new approach to VIT simulations where the overall TKE is calculated as a function of number of vehicles. We found that the interactions between vehicles traveling next to each other in adjacent lanes are insignificant,regardless the directions of the traffic flow. Consequently, simulations of different traffic scenarios can be substantially simplified by treating two-way traffic as one-way traffic, with less than 5% difference in the overall volume-averaged TKE. We also developed equations that allow the estimation of the overall volume-averaged TKE as a function of the number and the type of vehicles.

Modeling study on the roles of the deposition and transport of PM_(2.5) in air quality changes over central-eastern China

The role of PM_(2.5)(particles with aerodynamic diameters≤_(2.5)μm)deposition in air quality changes over China remains unclear.By using the three-year(2013,2015,and 2017)simulation results of the WRF/CUACE v1.0 model from a previous work(Zhang et al.,2021),a non-linear relationship between the deposition of PM_(2.5)and anthropogenic emissions over central-eastern China in cold seasons as well as in different life stages of haze events was unraveled.PM_(2.5)deposition is spatially distributed differently from PM_(2.5)concentrations and anthropogenic emissions over China.The North China Plain(NCP)is typically characterized by higher anthropogenic emissions compared to southern China,such as the middlelow reaches of Yangtze River(MLYR),which includes parts of the Yangtze River Delta and the Midwest.However,PM_(2.5)deposition in the NCP is significantly lower than that in the MLYR region,suggesting that in addition to meteorology and emissions,lower deposition is another important factor in the increase in haze levels.Regional transport of pollution in central-eastern China acts as a moderator of pollution levels in different regions,for example by bringing pollution from the NCP to the MLYR region in cold seasons.It was found that in typical haze events the deposition flux of PM_(2.5)during the removal stages is substantially higher than that in accumulation stages,with most of the PM_(2.5)being transported southward and deposited to the MLYR and Sichuan Basin region,corresponding to a latitude range of about 24°N-31°N.

Influences of Meteorological Conditions on Interannual Variations of Particulate Matter Pollution during Winter in the Beijing–Tianjin–Hebei Area

To investigate the interannual variations of particulate matter （PM） pollution in winter, this paper examines the pollution characteristics of PM with aerodynamic diameters of less than 2.5 and 10 μm （i.e., PM2.5 and PM10）, and their relationship to meteorological conditions over the Beijing municipality, Tianjin municipality, and Hebei Province--an area called Jing-Jin-Ji （JJJ, hereinafter）-in December 2013-16. The meteorological conditions during this period are also analyzed. The regional average concentrations of PM2.5 （PM10） over the JJJ area during this period were 148.6 （236.4）, 100.1 （166.4）, 140.5 （204.5）, and 141.7 （203.1） μg m^-3, respectively. The high occurrence frequencies of cold air outbreaks, a strong Siberian high, high wind speeds and boundary layer height, and low temperature and relative humidity, were direct meteorological causes of the low PM concentration in December 2014. A combined analysis of PM pollution and meteorological conditions implied that control measures have resulted in an effective improvement in air quality. Using the same emissions inventory in December 2013-16, a modeling analysis showed emissions of PM2.5 to decrease by 12.7%, 8.6%, and 8.3% in December 2014, 2015, and 2016, respectively, each compared with the previous year, over the JJJ area.

Updated Simulation of Tropospheric Ozone and Its Radiative Forcing over the Globe and China Based on a Newly Developed Chemistry–Climate Model

This study evaluates the performance of a newly developed atmospheric chemistry–climate model,BCCAGCM_CUACE2.0(Beijing Climate Center Atmospheric General Circulation Model_China Meteorological Administration Unified Atmospheric Chemistry Environment)model,for determining past(2010)and future(2050)tropospheric ozone(O_(3))levels.The radiative forcing(RF),effective radiative forcing(ERF),and rapid adjustments(RAs,both atmospheric and cloud)due to changes in tropospheric O_(3)are then simulated by using the model.The results show that the model reproduces the tropospheric O_(3)distribution and the seasonal changes in O_(3)surface concentration in 2010 reasonably compared with site observations throughout China.The global annual mean burden of tropospheric O_(3)is simulated to have increased by 14.1 DU in 2010 relative to pre-industrial time,particularly in the Northern Hemisphere.Over the same period,tropospheric O_(3)burden has increased by 21.1 DU in China,with the largest increase occurring over Southeast China.Although the simulated tropospheric O_(3)burden exhibits a declining trend in global mean in the future,it increases over South Asia and Africa,according to the Representative Concentration Pathway(RCP)4.5 and 8.5 scenarios.The global annual mean ERF of tropospheric O_(3)is estimated to be 0.25 W m^(−2)in 1850−2010,and it is 0.50 W m^(−2)over China.The corresponding atmospheric and cloud RAs caused by the increase of tropospheric O_(3)are estimated to be 0.02 and 0.03 W m^(−2),respectively.Under the RCP2.6,RCP4.5,RCP6.0,and RCP8.5 scenarios,the annual mean tropospheric O_(3)ERFs are projected to be 0.29(0.24),0.18(0.32),0.23(0.32),and 0.25(0.01)W m^(−2)over the globe(China),respectively.

Wavelet Galerkin Methods for Aerosol Dynamic Equations in Atmospheric Environment

Aerosol modelling is very important to study and simulate the behavior of aerosol dynamics in atmospheric environment.In this paper,we consider the general nonlinear aerosol dynamic equations which describe the evolution of the aerosol distribution.Continuous time and discrete time wavelet Galerkin methods are proposed for solving this problem.By using the Schauder’s fixed point theorem and the variational technique,the global existence and uniqueness of solution of continuous time wavelet numerical methods are established for the nonlinear aerosol dynamics with sufficiently smooth initial conditions.Optimal error estimates are obtained for both continuous and discrete time wavelet Galerkin schemes.Numerical examples are given to show the efficiency of the wavelet technique.