Measurement report: Insights into seasonal dynamics and planetary boundary layer influences on aerosol chemical components in suburban Nanjing from one-year observation

Abstract

Understanding the seasonal behavior of fine particles (PM2.5) and its chemical components is critical for improving air quality in the Yangtze River Delta (YRD), a densely populated and polluted region in China. While previous studies have addressed PM2.5 mass trends, the role of planetary boundary layer height (PBLH) in modulating chemical composition remains insufficiently explored. This study investigates seasonal variations and PBLH effects on PM2.5 chemical components based on year-round field measurements (December 2020-November 2021) at Nanjing University of Information Science and Technology. Annual mean PM2.5 mass concentration is 30.0±18.5μgm-3, with winter peaks (48.3 μgm-3) and summer lows (20.4 μgm-3). Organic aerosol dominates PM2.5, followed by sulfate in warmer seasons and nitrate in winter. Stable meteorological conditions promote the accumulation of primary aerosols and nitrate. The accumulation of SOA and sulfate remains substantial under elevated PBLH conditions, owing to strong photochemical production, rendering them relatively insensitive to PBLH variations. In contrast, during cold and humid winters, shallow PBLH promotes nitrate buildup, which subsequently suppresses boundary layer development, forming positive feedback that accelerates nitrate concentration growth. Source apportionment reveals that the contrasting seasonal sources, shaped by both local chemistry and regional transport, emphasize the need for seasonally adaptive and region-specific emission control measures.