Understanding the influence of particle growth on air quality and local climate in megacity

New particle formation (NPF) is a process in which gaseous molecules in the atmosphere cluster together to form aerosol particles [1]. These particles contribute significantly to the total number of aerosols in the atmosphere, further influencing air quality and climate [2]. The environmental and climate effects of NPF largely depend on the particle growth (NPG) process; however, it remains poorly understood, especially in urban [3]. In this study, we performed simultaneous measurements of particle number size distributions (PNSD) and chemical compositions at the ground and at 260 m based on the 325 m meteorological tower in urban Beijing. By comparing the NPG process at the two heights, we provide new insights into the interactions between boundary layer dynamics and NPG in megacity [4, 5].
Our results show that although NPG occurred at both heights, significant differences of NPG between 260 m and the ground level were observed in megacity. When vertical diffusion is sufficient, gaseous precursors from the surface could be transported to higher altitudes. The lower temperature and higher relative humidity aloft promoted gas-to-particle conversion, leading to stronger particle growth at higher altitudes. As a result, higher particle concentrations accompanied by stronger hygroscopicity led to >20% higher NPF-induced cloud condensation nuclei (CCN) formation aloft. However, when vertical mixing was suppressed, gaseous pollutants tended to accumulate near the surface. These pollutants then contributed to particle growth at ground level, exacerbating atmospheric haze pollution near ground. This, in turn, further reduced the boundary layer height. The valuable results provided novel information of the interactions between boundary layer dynamics and new particle growth, enhancing our understanding on the climate and environmental effects of NPF.
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5.    Du, W., et al., Impacts of enhanced new-particle growth events above urban roughness sublayer on cloud condensation nuclei. One Earth, 2024.