In Preparation
Gao, C. Y., S. E. Bauer, and K. Tsigaridis. “The Impact of Organic Aerosol Volatility on Radiative Forcing and Climate.” n. pag. Print.
Gao, C. Y. et al. “How Well Do We Model Aerosols over Remote Oceans During ATom?.” n. pag. Print.
Gao, C. Y., S. E. Bauer, and K. Tsigaridis. “The Impact of Organic Aerosol Volatility on Aerosol Microphysics and Aerosol Activation on the Global Scale.” n. pag. Print.
2020
Li, X. et al. “Atmospheric Boundary Layer Turbulence Structure for Severe Foggy Haze Episodes in North China in December 2016.” Environmental Pollution 264 (2020): 114726.
Abstract
This paper aims to identify the atmospheric boundary layer turbulence structure and its effect on severe foggy haze events frequently occurring in Northern China. We use data collected from a ground eddy covariance system, meteorology tower, and a PM2.5 collector in Baoding, China during December 2016. The data shows that 73.5% of PM2.5 concentration is greater than 100 μg m−3 with a maximum of 522 μg m−3. Analyses on vertical turbulence spectrum also reveal that 1) during the pollution period, lower wind can suppress large-scale turbulence eddies, which are more likely inhomogeneous, breaking into small-scale eddies, and 2) the air pollutant scattering effect for radiation could decrease the air temperature near the ground and generate weak vertical turbulence during the daytime. At night, air pollutants suppress the land surface cooling and decrease the air temperature difference as well as the vertical turbulence intensity difference. The vertical turbulence impact analysis reveals that the percentage of large-scale turbulence eddies can also change the atmospheric vertical mixing capacity. During the daytime, the air pollution evolution is controlled by the wind speed and vertical turbulence intensity. While at night, the vertical turbulence is weak and the atmospheric vertical mixing capacity is mainly controlled by the large-scale eddies’ percentage. The increased number of large-scale turbulence eddies led by low wind at night could increase the vertical mixing of air pollutants and decrease its concentration near the ground.
2019
Yin, J. et al. “Surface Meteorological Conditions and Boundary Layer Height Variations During an Air Pollution Episode in Nanjing, China.” Journal of Geophysical Research: Atmospheres 124.6 (2019): 3350–3364.
Abstract
Abstract The evolution of planetary boundary layer (PBL) was investigated using observations from a laser ceilometer, an eddy covariance system, and an automatic meteorological station in the north of Nanjing city during an air pollution episode in 2016–2017 winter. Based on 7-day observation under clean to polluted day, we recorded the temporal variations of backscatter signals observed by the ceilometer, and then intercompared the planetary boundary layer height (PBLH) retrieved from individual methods. The results show that backscatter signal gradient, standard deviation, and wavelet transform analysis methods generated similar PBLH values and PBL diurnal variation patterns. Moreover, the PBL structure varied diurnally, with distinct patterns corresponding to clean and polluted days. Based on these measurements, the relationships between PBLH, weather conditions, and contaminants were analyzed. Results show that on clean days, strong surface turbulence exchange makes the PBL fully developed and makes the PBLH increase sharply after sunrise, with a maximum of 1,483 m; on polluted days, stable synoptic conditions and the weaker wind speeds facilitated the accumulation of air pollutants, leading to smaller net surface radiation and weaker turbulence. Consequently, these conditions during polluted days led to lower PBLH values, which were typically less than 900 m.
Bauer, S. E. et al. “Desert Dust, Industrialization, and Agricultural Fires: Health Impacts of Outdoor Air Pollution in Africa.” Journal of Geophysical Research: Atmospheres 124.7 (2019): 4104–4120.
Abstract
Abstract The African continent continuously experiences extreme aerosol load conditions, during which the World Health Organization clean air standard of 10 μg/m3 of PM2.5 mass is systematically exceeded. Africa holds the world largest source of desert dust emissions, undergoes strong industrial growth, and produces approximately a third of the Earth's biomass burning aerosol particles. Sub-Saharan biomass burning is driven by agricultural practices, such as burning fields and bushes in the postharvest season for fertilization, land management, and pest control. Thus, these emissions are predominantly anthropogenic. Here we use global atmospheric composition, climate, and health models to simulate the chemical composition of the atmosphere and calculate the mortality rates for Africa by distinguishing between purely natural, industrial/domestic, and biomass burning emissions. Air quality-related deaths in Africa rank within the top leading causes of death in Africa. Our results of 780,000 premature deaths annually point to the extensive health impacts of natural emissions, high mortality rate caused by industrialization in Nigeria and South Africa, and a smaller extent by fire emissions in Central and West Africa. In Africa, 43,000 premature deaths are linked to biomass burning mainly driven by agriculture. Our results also show that natural sources, in particular windblown dust emissions, have large impacts on air quality and human health in Africa.
Li, Xin et al. “Meteorological Conditions for Severe Foggy Haze Episodes over North China in 2016–2017 Winter.” Atmospheric Environment 199 (2019): 284–298.
Abstract
This paper aims to identify the meteorological conditions of severe foggy haze events that frequently occurred over North China. We analyzed data collected at 162 ground observation stations operated by China Meteorological Administration (CMA), as well as data from National Centers Environmental Prediction (NCEP) over North China from December 1, 2016 to January 9, 2017. During this period, more than 72% of the regional mean atmospheric visibility was less than 10 km, with a minimum of 1.15 km. The analysis on atmospheric background fields revealed that during the pollution development-maintenance period there were southerlies and lower wind speed in the lower troposphere compared to that during the pollution dissipation period. Slow southerlies transported the southern pollutants to North China, while high pressure system at the 500 hPa level and increasing temperature (caused by air pollutant absorbed radiation) at 850 hPa suppressed the convection and led to pollutants accumulation over the ground. During the pollution dissipation period, there were northerlies and higher wind speed, and the fast northerlies quickly transported the pollutants. The analysis on the dynamic and thermodynamic effect suggests that the smaller horizontal wind vertical shear is attributed to 500 hPa decreased wind speed. The air pollutant warming effect on 850 hPa from absorbed solar radiation and cooling effect on near surface from reduced radiation near surface could lead to a larger correlation between atmospheric visibility and thermodynamic conditions for more than 76%. This coupling structure between air pollutant and thermodynamic situation provide favorable conditions for foggy haze events under air pollutant transport and weak vertical exchange conditions. Therefore, in order to predict foggy haze episodes in North China, we need to better understand its dynamics, especially for decreased middle level wind speed and lower level south flow.
Liu, C. et al. “Surface Energy Budget Observed for Winter Wheat in the North China Plain During a Fog–Haze Event.” Boundary-Layer Meteorology 170.3 (2019): 489–505.
Abstract
In recent winters, fog–haze events have occurred frequently over the North China Plain. To understand the characteristics of conventional meteorological conditions, the near-surface radiation balance, and the surface energy budget under different pollution levels, we analyzed data collected at an observation site in Gucheng, which is located in the Hebei province in North China, based on a campaign that ran from December 1 2016 to January 31 2017. We found that meteorological conditions with a lower wind speed, weakly unstable (stable) stratification, higher relative humidity, and lower surface pressure during the daytime (night-time) are associated with fog–haze events. On heavy pollution days (defined as days with a daily mean PM2.5 concentration > 150 μg m−3), the decrease in downward shortwave radiation (S↓) and the increase in downward longwave radiation (L↓) are significant. The mean S↓ (L↓) values on clean-air days (daily mean PM2.5 concentration < 75 μg m−3) and heavily polluted days was 222 (222) W m−2 and 124 (265) W m−2, respectively. Due to the negative (positive) radiative forcing of aerosols during the daytime (night-time), the daily maximum (night-time mean) net radiation (Rn) is negatively (positively) related to the daily mean PM2.5 concentration, the correlation coefficient between the daily maximum (night-time mean) Rn and daily mean PM2.5 concentration being − 0.47 (0.51). Diurnal variations in sensible heat flux (H) and latent heat flux (λE) are insignificant on heavily polluted days, the mean daily maximum H (λE) is only 40 (28) W m−2 on heavily polluted days, but reaches 90 (42) W m−2 on clean-air days. Additionally, the friction velocity, standard deviation of vertical velocity, and turbulent kinetic energy on heavily polluted days are also quantified.
2018
Gao, C. Y., S. E. Bauer, and K. Tsigaridis. “Can Semi-Volatile Organic Aerosols Lead to Fewer Cloud Particles?.” Atmospheric Chemistry and Physics 18.19 (2018): 14243–14251.
Abstract
The impact of condensing organic aerosols on activated cloud number concentration is examined in a new aerosol microphysics box model, MATRIX-VBS. The model includes the volatility basis set (VBS) framework coupled with the aerosol microphysical scheme MATRIX (Multiconfiguration Aerosol TRacker of mIXing state) that resolves aerosol mass and number concentrations and aerosol mixing state. By including the condensation of organic aerosols, the new model produces fewer activated particles compared to the original model, which treats organic aerosols as nonvolatile. Parameters such as aerosol chemical composition, mass and number concentrations, and particle sizes that affect activated cloud number concentration are thoroughly tested via a suite of Monte Carlo simulations. Results show that by considering semi-volatile organics in MATRIX-VBS, there is a lower activated particle number concentration, except in cases with low cloud updrafts, in clean environments at above-freezing temperatures, and in polluted environments at high temperatures (310 K) and extremely low-humidity conditions.
Liu, J. et al. “The Impact of Urbanization on Wind Speed and Surface Aerodynamic Characteristics in Beijing During 1991–2011.” Meteorology and Atmospheric Physics 130.3 (2018): 311–324.
Abstract
Urbanization has a significant influence on climate and meteorological conditions through altering surface aerodynamic characteristics. Based on observational data collected at 15 levels on a 325 m meteorological tower in Beijing during 1991–2011, changes in wind speed, vertical profile, aerodynamic roughness length (\$\$z\_\0\\$\$z0), and zero-plane displacement height (\$\$z\_\\backslashtext\d\\\$\$zd) were analyzed. Decreasing trends were observed predominantly during this period, especially for levels between 65 and 140 m where the largest decreasing rates often occur. The annual and seasonal (spring, summer, autumn, and winter) mean wind speeds at 15 levels all present decreasing trends with average rates of 0.029, 0.024, 0.023, 0.040, and 0.019 m s−1 a−1, respectively. The decreases in strong wind categories contribute most to the reduction of mean wind speed. Furthermore, in 2005–2011, the diurnal maximum wind speeds at lower levels tend to appear earlier as compared to those in 1991–1997, while the patterns of diurnal cycle between different levels become more similar in these periods. Besides, the phenomena of ``kink'' in wind profiles are visible in various atmospheric stabilities, and the average height of a kink has increased from about 40 m to nearly 80 m associated with urbanization during 1991–2011. In addition, the results of \$\$z\_\0\\$\$z0and \$\$z\_\\backslashtext\d\\\$\$zdcalculated using the wind profile method vary with wind directions due to surface heterogeneity and that larger values often occur along with southerly winds. Both \$\$z\_\0\\$\$z0and \$\$z\_\\backslashtext\d\\\$\$zdshow increasing trends in different sectors during 1991–2011, and the annual mean \$\$z\_\0\\$\$z0and \$\$z\_\\backslashtext\d\\\$\$zdhave increased from less than 1 m to greater than 2 m, and from less than 10 m to greater than 20 m, respectively.
Liu, J. et al. “Wind Resource Potential Assessment Using a Long Term Tower Measurement Approach: A Case Study of Beijing in China.” Journal of Cleaner Production 174 (2018): 917–926.
Abstract
With exacerbating air quality due to pollutant emissions and rising energy supply crisis, the wind energy consumption will play a key role in future energy structure in China. To utilize the wind energy optimally, a better understanding and quantification of wind resource such as the temporal-spatial and vertical distributions is vital prior to exploitation. Based on wind measurements from 1991 to 2011 on a 15-level 325 m meteorological tower in Beijing, we assessed the potential of wind resource using the Weibull function and the wind atlas analysis and application program (WAsP) software. Results show that wind resource has significant seasonal and diurnal variations and diurnal variation varies with height. Additionally, although the wind resource increases with height, there is a strong wind shear layer related to the complex urban underlying surface. Furthermore, observation and WAsP simulation show that larger wind resource mainly comes from northwest wind in northwestern or northern Beijing. However, considering the regional average wind resource, we concluded that wind resource in Beijing is suitable for small wind turbines, yet the decreasing trends of wind resources seem to make wind energy unsustainable.
2017
Gao, C. Y., K. Tsigaridis, and S. E. Bauer. “MATRIX-VBS (v1.0): Implementing an Evolving Organic Aerosol Volatility in an Aerosol Microphysics Model.” Geoscientific Model Development 10.2 (2017): 751–764.
Abstract
The gas-particle partitioning and chemical aging of semi-volatile organic aerosol are presented in a newly developed box model scheme, where its effect on the growth, composition, and mixing state of particles is examined. The volatility-basis set (VBS) framework is implemented into the aerosol microphysical scheme MATRIX (Multiconfiguration Aerosol TRacker of mIXing state), which resolves mass and number aerosol concentrations and in multiple mixing-state classes. The new scheme, MATRIX-VBS, has the potential to significantly advance the representation of organic aerosols in Earth system models by improving upon the conventional representation as non-volatile particulate organic matter, often also with an assumed fixed size distribution. We present results from idealized cases representing Beijing, Mexico City, a Finnish forest, and a southeastern US forest, and investigate the evolution of mass concentrations and volatility distributions for organic species across the gas and particle phases, as well as assessing their mixing state among aerosol populations. Emitted semi-volatile primary organic aerosols evaporate almost completely in the intermediate-volatility range, while they remain in the particle phase in the low-volatility range. Their volatility distribution at any point in time depends on the applied emission factors, oxidation by OH radicals, and temperature. We also compare against parallel simulations with the original scheme, which represented only the particulate and non-volatile component of the organic aerosol, examining how differently the condensed-phase organic matter is distributed across the mixing states in the model. The results demonstrate the importance of representing organic aerosol as a semi-volatile aerosol, and explicitly calculating the partitioning of organic species between the gas and particulate phases.