Vertically-resolved sources and secondary formation of fine particles: A high resolution tethered mega-balloon study over Shanghai

Numerous studies have focused on air pollution near the surface in China, yet we still have little knowledge on the characteristics, formation mechanisms, and sources of air pollutants aloft. Based on a tethered mega-balloon platform, the vertical profiles of PM_2.5, black carbon (BC), SO₂, O₃, and meteorological parameters were measured within the lower troposphere of 1000 m over Shanghai. One clean and slightly polluted period (CP) and one heavily polluted period (HP) with continuously measured profiles were compared. The potential source areas of PM_2.5 at different altitudes during HP were determined based on the time-lag spatial correlation analysis, indicating the surrounding regions were the main sources of low-altitude particles in Shanghai and farther regions of northern China significantly affected the upper atmosphere. By apportioning the sources of vertical BC profiles, fossil fuel combustion contributed >80% to BC below 600 m during HP, exhibiting a higher contribution than CP. An indicator (i.e. SA/SO₂, SA represents secondary aerosols) was established to investigate the vertical evolution of secondary aerosol formation. During CP, relatively low SA/SO₂ ratios were observed within the boundary layer due to the weak atmospheric processing. SA/SO₂ profiles showed the opposite vertical trend of higher ratios below about 600 m while lower values at high altitudes during HP. Regional and long-range transport regulated the extents of secondary aerosol formation. Northeasterlies transported abundant aged aerosols from northern China while sea breezes suppressed the columnar secondary aerosol formation. This study provided insights into the vertical structures of typical air pollutants in a Chinese megacity and implied that high-resolution measurements of atmospheric vertical profiles were valuable for diagnosing sources and potential secondary formation of fine particles.

Three-dimensional investigation of ozone pollution in the lower troposphere using an unmanned aerial vehicle platform

Potential utilities of instrumented lightweight unmanned aerial vehicles (UAVs) to quickly characterize tropospheric ozone pollution and meteorological factors including air temperature and relative humidity at three-dimensional scales are highlighted in this study. Both vertical and horizontal variations of ozone within the 1000 m lower troposphere at a local area of 4 × 4 km² are investigated during summer and autumn times. Results from field measurements show that the UAV platform has a sufficient reliability and precision in capturing spatiotemporal variations of ozone and meteorological factors. The results also reveal that ozone vertical variation is mainly linked to the vertical distribution patterns of air temperature and the horizontal transport of air masses from other regions. In addition, significant horizontal variations of ozone are also observed at different levels. Without major exhaust sources, ozone horizontal variation has a strong correlation with the vertical convection intensity of air masses within the lower troposphere. Higher air temperatures are usually related to lower ozone horizontal variations at the localized area, whereas underlying surface diversity has a week influence. Three-dimensional ozone maps are obtained using an interpolation method based on UAV collected samples, which are capable of clearly demonstrating the diurnal evolution processes of ozone within the 1000 m lower troposphere.

Global tropospheric ozone dynamics. Part I: Tropospheric ozone precursors

An overview of the tropospheric ozone changes is presented focussing mainly on the tropospheric ozone precursors. The complexity of the problem is shown through the consideration of a great number of relevant substances, like nitrogen compounds, volatile organic compounds, peroxyacetyl nitrate, hydroxyl radical, carbon monoxide, alkyl nitrates. The up-to-date knowledge on the relevant numerical modelling is presented in Part II.