Extended Data Fig. 10: Case showing the selection of SOA formation episode.
From: Secondary organic aerosol formed by condensing anthropogenic vapours over China’s megacities
A stable weather condition is critical for selecting SOA formation episodes to exclude the influence of air mass changes. Four parameters, including wind speed, wind direction, boundary layer height and water concentrations, are used for the judgement. For one sampling period, when these four parameters kept stable, it can be identified as a SOA episode. These selected SOA episodes mostly concentrated around noontime or night-time time when the boundary layer was stable. In total, 16 episodes in Beijing, 19 episodes in Nanjing, 8 episodes in Shanghai, and 18 episodes in Hong Kong were selected for further analysis. We also test the potential uncertainties from case selection by varying the start- and end-point of the case. Cases with the uncertainties of d(SOA)/dt higher than 30% are excluded.
