1Institute for Environmental and Climate Research, Jinan University, Guangzhou, China
2Key Laboratory of Regional Numerical Weather Prediction, Institute of Tropical and Marine Meteorology, China Meteorological Administration, Guangzhou, 510640, China
3Guangdong-Hongkong-Macau Joint Laboratory of Collaborative Innovation for Environmental Quality, Guangzhou, China
4State Key Laboratory of Severe Weather & Key Laboratory for Atmospheric Chemistry, Institute of Atmospheric Composition, Chinese Academy of Meteorological Sciences, Beijing, 100081, China
5Xiamen Key Laboratory of Straits Meteorology, Xiamen Meteorological Bureau, Xiamen, 361012, China
6Experimental Teaching Center, Sun Yat-Sen University, Guangzhou 510275, China
7Shanghai Key Laboratory of Meteorology and Health, Shanghai Meteorological Bureau, Shanghai 200030, China
1Institute for Environmental and Climate Research, Jinan University, Guangzhou, China
2Key Laboratory of Regional Numerical Weather Prediction, Institute of Tropical and Marine Meteorology, China Meteorological Administration, Guangzhou, 510640, China
3Guangdong-Hongkong-Macau Joint Laboratory of Collaborative Innovation for Environmental Quality, Guangzhou, China
4State Key Laboratory of Severe Weather & Key Laboratory for Atmospheric Chemistry, Institute of Atmospheric Composition, Chinese Academy of Meteorological Sciences, Beijing, 100081, China
5Xiamen Key Laboratory of Straits Meteorology, Xiamen Meteorological Bureau, Xiamen, 361012, China
6Experimental Teaching Center, Sun Yat-Sen University, Guangzhou 510275, China
7Shanghai Key Laboratory of Meteorology and Health, Shanghai Meteorological Bureau, Shanghai 200030, China
Received: 30 Nov 2022 – Discussion started: 22 Dec 2022
Abstract. Emission controls have substantially brought down aerosol pollution in China, however, aerosol mass reductions have slowed down in recent years in the Pearl River Delta (PRD) region, where secondary organic aerosol (SOA) formation poses a major challenge for air quality improvement. In this study, we characterized the roles of SOA in haze formation in urban Guangzhou City of the PRD using year-long aerosol mass spectrometer measurements for the first time and discussed possible pathways of SOA formations. On average, organic aerosols (OA) contribute dominantly (50 %) to non-refractory submicron aerosol mass (NR-PM1). The average mass concentration of SOA (including by less and more oxidized OA, LOOA and MOOA) contributed most to NR-PM1, reaching about 1.7 times that of primary organic aerosols (POA, including hydrocarbon-like and cooking-related OA) and accounting for 32 % of NR-PM1, even more than sulfate (22 %) and nitrate (16 %). Seasonal variations of NR-PM1 revealed that haze formation mechanisms differed much among distinct seasons. Sulfate mattered more than nitrate in fall, while nitrate was more important than sulfate in spring and winter, with SOA contributing significantly to haze formations in all seasons. Daytime SOA formation was weak in winter under low oxidant level and air relative humidity, whereas prominent daytime SOA formation was observed in fall, spring and summer almost on daily basis, suggesting for important roles of photochemistry in SOA formations. Further analysis showed that the coordination of gas-phase photochemistry and subsequent aqueous-phase reactions likely played significant roles in quick daytime SOA formations. Obvious nighttime SOA formations were also frequently observed in spring, fall and winter, and it was found that daytime and nighttime SOA formations together had resulted in the highest SOA concentrations in these seasons and contributed substantially to severe haze formations. Simultaneous increases of nitrate with SOA after sunset suggested the important roles of NO3 radical chemistry in nighttime SOA formations, and confirmed by continuous increase of NO+/NO2+ fragment ratio after sunset. Findings of this study have promoted our understanding in haze pollution characteristics of the PRD and laid down future directions on investigations of SOA formation mechanisms in urban areas of southern China that share similar emission sources and meteorological conditions.
The Pearl River Delta (PRD) region is an important area for air quality research. This study provides a year-long observation of aerosol species using aerosol mass spectrometry. The paper’s focus is given to secondary organic aerosols which account for about a quarter of submicron particle mass concentration. In general, the paper is well organized and clearly written. Presenting such an extensive observational dataset itself serves as a contribution to the atmospheric chemistry community. I only have a few minor comments on the current paper.
On the Q-ACSM data analysis: Previous studies used to have different categories for SOAs. For example, some studies have separated an aq-SOA (aqueous-processing SOA) component. Can the authors provide more information on the assumption and reasons for their choice of SOA categories?
Fig.3 & Fig.5: Earlies studies reported fast formation of sulfate at haze episodes, which seems to be different from the measurements shown here. Can the authors show the reasons?
The variations of boundary layer height may affect the interpretation of the formation mechanisms of aerosol species. Can the authors provide more quantitative results on its influence?
Using year-long aerosol mass spectrometer measurements, roles of secondary organic aerosols (SOA) during haze formations in urban area of southern China were systematically analyzed. Almost all severe haze events were accompanied by continuous daytime and nighttime SOA formations, whereas coordinated gas-phase photochemistry and aqueous-phase reactions likely played significant roles in quick daytime SOA formations, and nitrate radical play significant roles in nighttime SOA formations.
Using year-long aerosol mass spectrometer measurements, roles of secondary organic aerosols...
