Mixing state of individual submicron carbon-containing particles during spring and fall seasons in urban Guangzhou, China: a case study

Abstract

Abstract. Growing evidence suggests that the size-resolved mixing state of carbon-containing particles is very critical in determining their optical properties, atmospheric lifetime, and impact on the environment. However, still little is known about the mixing state of particles in the urban area of the Pearl River Delta (PRD) region, China. To investigate the mixing state of submicron carbon-containing particles, measurements were carried out during spring and fall periods of 2010 using a single-particle aerosol mass spectrometer (SPAMS). Approximately 700 000 particles for each period were detected. This is the first report on the size-resolved mixing state of carbon-containing particles by direct observations in the PRD region. Cluster analysis of single-particle mass spectra was applied to identify carbon-containing particle classes. These classes represented ~80% and ~90% of all the detected particles for spring and fall periods, respectively. Carbon-containing particle classes mainly consisted of biomass/biofuel burning particles (Biomass), organic carbon (OC), fresh elemental carbon (EC-fresh), internally mixed OC and EC (ECOC), internally mixed EC with sulfate (EC-Sulfate), vanadium-containing ECOC (V-ECOC), and amines-containing particles (Amine). In spring, the top three ranked carbon-containing particle classes were ECOC (26.1%), Biomass (23.6%) and OC (10%), respectively. However, the fraction of Biomass particles increased remarkably and predominated (61.0%), while the fraction of ECOC (3.0%) and V-ECOC (0.1%) significantly decreased in fall. To highlight the influence of monsoon on the properties of carbon-containing particles in urban Guangzhou, their size distributions, mixing state, and aerosol acidity were compared between spring and fall seasons. In addition, a case study was also performed to investigate how the formation of fog and haze influenced the mixing state of carbon-containing particles. These results could improve our understanding of the mixing state of carbon-containing particles, and may also be helpful in modeling the climate forcing of aerosol in the PRD region.

Variation of secondary coatings associated with elemental carbon by single particle analysis

“…The different mixing state of EC in this study can be attributed to various reasons (e.g., source and atmospheric processes). These results reveal that hydrophobic EC was commonly coated and/or coagulated with hygroscopic secondary materials in the atmosphere of the PRD region, which is consistent with previous studies in the same region (Zhang et al, 2013a), Yangtze River Delta region , northern China and Mexico city (Adachi and Buseck, 2008;Moffet and Prather, 2009). These hygroscopic coatings on EC particles can amplify their light absorption and growth through the absorption of water, and thus may lead to a greater effect on the formation of haze and regional climate.…”

“…It represented the dominant fraction (w70%) in the size range of 0.2e0.3 mm, and decreased to w30% for larger particles (>0.5 mm). The distribution pattern is generally consistent with our previous study conducted in an urban area of the PRD region (Zhang et al, 2013a).…”

Characteristics of individual particles in the atmosphere of Guangzhou by single particle mass spectrometry

“…Secondary inorganic species like sulfate, nitrate and ammonium were commonly detected in different single particle types with different intensities (Cahill et al, 2012;Zhang et al, 2013). The presence of secondary species on the particle types provides an indication of chemical processes in the atmosphere (Spencer et al, 2008).…”

“…The single particle studies have showed that there are many particle types with complex mixing state in the urban areas (e.g., Moffet et al, 2008a;Zhang et al, 2013). The physical and chemical properties (including density, shape, hygroscopicity, and refractive index) of these particle types are distinctly different from each other, influenced by various factors such as meteorological conditions and emission sources (e.g., Moffet and Prather, 2009;Zelenyuk et al, 2008).…”

“…It has been utilized to characterize size and mixing state of both ambient and laboratory generated aerosols, greatly improving the understanding on the aging processes, source, and optical properties of atmospheric aerosols Spencer et al, 2008;Sullivan et al, 2007). In China, on-line single particle mass spectrometry has most recently been applied in the studies on physicochemical properties of individual particles and their potential influence on air quality (Chen et al, 2014;Yang et al, 2012), and the related researches have investigated the mixing state of carbonaceous particles in the atmosphere of the PRD region Zhang et al, 2013). However, knowledge on the mixing state of atmospheric aerosols in the PRD region was still limited.…”