Ground-based formaldehyde across the Pearl River Delta: A snapshot and meta-analysis study

Abstract

Formaldehyde (HCHO) is one of the most abundant carbonyls in the troposphere, which plays a significant role in atmospheric chemistry. Limited knowledge is available on the spatial fingerprints and long-term trends of ground-based HCHO in megacity clusters of China. Here we performed a concurrent multi-site observation during a photochemical episode in autumn 2021 and conducted a temporal trend analysis of HCHO in the Pearl River Delta (PRD) region, southern China. The HCHO concentrations were found to be sensitive to the land-use types in the order of urban > suburban > rural. The predominant sources of HCHO in the morning and afternoon were primary emissions and secondary formations, respectively. Extremely high concentrations of HCHO were captured in the Pearl River Estuary (PRE) area, and shipping emissions might be a plausible explanation for this unexpected phenomenon. O3 sensitivity analysis showed that the PRE area was in a VOC-limited regime during the episode. Meta-analysis demonstrated a U-shaped trend of HCHO in the PRD over the past two decades, exhibiting a “Seesaw effect” between particulate and photochemical pollutants after 2013. The snapshot and meta-analysis of ground-based HCHO in this study highlight the importance of ship-related HCHO in the PRE and in-depth investigation of reactive carbonyls from ship emissions will be in demand. Our results would be helpful for the assessment of past and future implementations of photochemical pollution control policy in the PRD region.