Characterization of aerosol optical properties, chemical composition and mixing states in the winter season in Shanghai, China

https://doi.org/10.1016/j.jes.2014.03.002Get rights and content

Abstract

Physical and chemical properties of ambient aerosols at the single particle level were studied in Shanghai from December 22 to 28, 2009. A Cavity-Ring-Down Aerosol Extinction Spectrometer (CRD-AES) and a nephelometer were deployed to measure aerosol light extinction and scattering properties, respectively. An Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) was used to detect single particle sizes and chemical composition. Seven particle types were detected. Air parcels arrived at the sampling site from the vicinity of Shanghai until mid-day of December 25, when they started to originate from North China. The aerosol extinction, scattering, and absorption coefficients all dropped sharply when this cold, clean air arrived. Aerosol particles changed from a highly aged type before this meteorological shift to a relatively fresh type afterwards. The aerosol optical properties were dependent on the wind direction. Aerosols with high extinction coefficient and scattering Ångström exponent (SAE) were observed when the wind blew from the west and northwest, indicating that they were predominantly fine particles. Nitrate and ammonium correlated most strongly with the change in aerosol optical properties. In the elemental carbon/organic carbon (ECOC) particle type, the diurnal trends of single scattering albedo (SSA) and elemental carbon (EC) signal intensity had a negative correlation. We also found a negative correlation (r =  0.87) between high mass-OC particle number fraction and the SSA in a relatively clean period, suggesting that particulate aromatic components might play an important role in light absorption in urban areas.

Introduction

Atmospheric aerosols have a “direct effect” on climate by scattering or absorbing solar radiation and an “indirect effect” by acting as cloud condensation and ice nuclei (Pöschl, 2005). The magnitude of these effects has still considerable uncertainties, especially the indirect effect (Forster et al., 2007, Schiermeier, 2010). In order to estimate the direct and indirect effect of aerosols, further understanding of aerosol optical properties is urgently needed.

The optical properties of aerosols govern their interaction with sunlight and are important parameters for estimating radiative forcing in modeling studies (Fischer et al., 2011). Studies have shown that aerosol optical properties are determined by particle size distribution, chemical components, and mixing state (Seinfeld and Pandis, 2006), with the latter being the most challenging to understand (Cappa et al., 2012, Huang et al., 2013). Different chemical species, especially soot and brown carbon (Lack and Cappa, 2010), can be mixed within a single particle (internal mixing) or across different particle types (external mixing); the exact mixing state changes aerosol optical properties and ultimately radiative forcing (Fuzzi et al., 2006, Ramanathan and Carmichael, 2008). Core–shell Mie theory has been widely used to calculate the theoretical aerosol optical properties (Jacobson, 2001). The coating shell on the cores often acts as a lens, enhancing the particle's absorbing and scattering ability, especially on black carbon cores (Lack and Cappa, 2010). However, field studies have shown that the theoretical model does not fit all cases (Cappa et al., 2012), and more work still needs to be done to investigate the influence of particle mixing state on aerosol optical properties.

Measurements of optical properties of aerosols along with mixing state within a single particle have been crucial in estimating aerosol radiative forcing (Pratt and Prather, 2010, McMeeking et al., 2011). Single particle mass spectrometers, such as the Aerosol Time-of-Flight Mass Spectrometer (ATOFMS), soot particle aerosol mass spectrometer (SP-AMS), and Single-Particle Soot Photometer (SP2), can provide information on the size-resolved chemical composition and internal mixing state of particles (Schwarz et al., 2006, Onasch et al., 2012, Pratt and Prather, 2012). Since SP-AMS and SP2 only measure material that is sufficiently light absorbing at 1064 nm (i.e., soot particles, and only the non-refractory aerosol component with SP-AMS), the ATOFMS is preferred for full chemical measurements in regions where sea salt or mineral dust is an important contributor to the aerosol.

In different regions of China, the majority of studies have been focused on the effect of the chemical mass concentration, aerosol physical properties and water content on the optical properties (Che et al., 2009, Guo et al., 2009, Jung et al., 2009a, Yang et al., 2009b, Yu et al., 2009, Eck et al., 2010, Huang et al., 2010, Wang et al., 2010). Jung et al. (2009b) found that under polluted conditions in the urban area of Beijing, ammonium sulfate, ammonium nitrate, and organic carbon contributed to the increases of single scattering albedo. Yao et al. (2010) analyzed atmospheric light extinction properties and chemical speciation of fine particulates in Shenzhen and concluded that the organic matter in PM1 contributed about 45% to the observed aerosol light extinction. Huang et al. (2011) measured black carbon (BC) mass loadings, size distributions and mixing state information in the Pearl River Delta region and estimated the potential contribution of BC mass to the radiative forcing. But studies of aerosol optical properties and their relationship with aerosol mixing state are very limited.

Cavity ring down spectroscopy (CRDS) has recently been used for measuring aerosol extinction and absorption coefficients in field and laboratory studies (Butler et al., 2007, Dinar et al., 2008, Zhang et al., 2008, Khalizov et al., 2009, Xue et al., 2009, Li et al., 2011, Li et al., 2013). Compared with filter based techniques like the Aethalometer and the Particle Soot Absorption Photometer (Bond et al., 1999, Sheridan et al., 2005), CRDS offers rapid real-time measurement of absorption coefficients (Busch and Busch, 1999, Pettersson et al., 2004, Bulatov et al., 2006). Huang et al. (2013) employed ATOFMS and CRDS to study the evolution of aerosol chemical and optical properties during a period in Shanghai when pollution was highly present. They found that organic carbon coatings could dramatically change aerosol optical properties, suggesting that this combination of measurements is ideal for elucidating the impact of particle mixing states on aerosol optical properties.

In this study, a Cavity-Ring-Down Aerosol Extinction Spectrometer (CRD-AES) (Li et al., 2011) and a nephelometer were used in Shanghai from 22 to 28 December, 2009 for the measurements of extinction and scattering coefficients, respectively. Simultaneously, an ATOFMS was used to obtain both positive and negative mass spectra from individual particles, and thus provide information on aerosol mixing state (Murphy, 2007). Examining these measurements concurrently, the sources of particles and the aerosol optical properties as a function of particle size distribution, chemical composition and mixing states are investigated.

Section snippets

Experimental

Measurements were carried out in the laboratory building of the Department of Environmental Science and Engineering at Fudan University (31°17′47.14″N, 121°30′14.94″E) in Shanghai from December 22 to December 28, 2009 (24 hr per day). This site is near residential, traffic, and construction emissions sources and represents a typical urban area. Ambient air was drawn from a height of about 5.5 m above the ground through a half-inch diameter, six-meter long, stainless steel tube at a flow rate of

Meteorology and optical measurement

The temporal profiles of temperature, relative humidity (RH), wind speed, and wind direction during the sampling period are shown in Fig. 1a. The time series of the aerosol optical properties at 532 nm, including the aerosol extinction, scattering and absorption coefficients are shown in Fig. 1b. The scattering Ångström exponent (å450/700, SAE) and single scattering albedo (SSA) are shown in Fig. 1c covering the entire sampling period. The backward air trajectories at 10 m height were determined

Conclusions

Measurements of aerosol optical and chemical properties were conducted from December 22 to December 29, 2009 in Shanghai, China. The aerosol optical properties were found to be dependent on the wind direction, and thus, are dependent on the source of the particles as well. The westerly wind usually brought particles with high extinction coefficient to the sampling site. The wind speed-resolved polar contour plots of PM10 and scattering Ångström indicated that particles originating in the

Acknowledgments

This work was supported by the National Natural Science Foundation of China (Nos. 21177027, 41275126), the Science & Technology Commission of Shanghai Municipality (Nos. 12DJ1400100, 14XD1400600), and the Jiangsu Provincial Collaborative Innovation Center of Climate Change.

References (68)

  • F. Yang et al.

    Evolution of the mixing state of fine aerosols during haze events in Shanghai

    Atmos. Res.

    (2012)
  • X.N. Yu et al.

    Ground-based observation of aerosol optical properties in Lanzhou, China

    J. Environ. Sci.

    (2009)
  • Y. Zhang et al.

    Source apportionment of lead-containing aerosol particles in Shanghai using single particle mass spectrometry

    Chemosphere

    (2009)
  • G. Adler et al.

    Chemical, physical, and optical evolution of biomass burning aerosols: a case study

    Atmos. Chem. Phys.

    (2011)
  • T.L. Anderson et al.

    Determining aerosol radiative properties using the TSI 3563 integrating nephelometer

    Aerosol Sci. Technol.

    (1998)
  • M.O. Andreae et al.

    Black carbon or brown carbon? The nature of light-absorbing carbonaceous aerosols

    Atmos. Chem. Phys.

    (2006)
  • S. Angelino et al.

    Formation of aerosol particles from reactions of secondary and tertiary alkylamines: characterization by aerosol time-of-flight mass spectrometry

    Environ. Sci. Technol.

    (2001)
  • P.V. Bhave et al.

    Source apportionment of fine particulate matter by clustering single-particle data: tests of receptor model accuracy

    Environ. Sci. Technol.

    (2001)
  • T.C. Bond et al.

    Calibration and intercomparison of filter-based measurements of visible light absorption by aerosols

    Aerosol Sci. Technol.

    (1999)
  • V. Bulatov et al.

    Absorption and scattering characterization of airborne microparticulates by a cavity ringdown technique

    Anal. Bioanal. Chem.

    (2006)
  • K.W. Busch et al.

    Cavity-Ringdown Spectroscopy

    (1999)
  • T.J.A. Butler et al.

    Cavity ring-down spectroscopy measurements of single aerosol particle extinction. I. The effect of position of a particle within the laser beam on extinction

    J. Chem. Phys.

    (2007)
  • J.F. Cahill et al.

    The mixing state of carbonaceous aerosol particles in northern and southern California measured during CARES and CalNex 2010

    Atmos. Chem. Phys.

    (2012)
  • C.D. Cappa et al.

    Radiative absorption enhancements due to the mixing state of atmospheric black carbon

    Science

    (2012)
  • E. Dinar et al.

    The complex refractive index of atmospheric and model humic-like substances (HULIS) retrieved by a cavity ring down aerosol spectrometer (CRD-AS)

    Faraday Discuss.

    (2008)
  • O. Dubovik et al.

    Variability of absorption and optical properties of key aerosol types observed in worldwide locations

    J. Atmos. Sci.

    (2002)
  • T.F. Eck et al.

    Climatological aspects of the optical properties of fine/coarse mode aerosol mixtures

    J. Geophys. Res.

    (2010)
  • E.V. Fischer et al.

    Optical and chemical properties of aerosols transported to Mount Bachelor during spring 2010

    J. Geophys. Res.

    (2011)
  • P. Forster et al.

    Changes in atmospheric constituents and in radiative forcing

  • S. Fuzzi et al.

    Critical assessment of the current state of scientific knowledge, terminology, and research needs concerning the role of organic aerosols in the atmosphere, climate, and global change

    Atmos. Chem. Phys.

    (2006)
  • E. Gard et al.

    Real-time analysis of individual atmospheric aerosol particles: design and performance of a portable ATOFMS

    Anal. Chem.

    (1997)
  • K. Huang et al.

    Relation between optical and chemical properties of dust aerosol over Beijing, China

    J. Geophys. Res.

    (2010)
  • X.F. Huang et al.

    Black carbon measurements in the Pearl River Delta region of China

    J. Geophys. Res.

    (2011)
  • K. Huang et al.

    Impact of anthropogenic emission on air quality over a megacity-revealed from an intensive atmospheric campaign during the Chinese Spring Festival

    Atmos. Chem. Phys.

    (2012)
  • Cited by (12)

    • Characteristics of volatile organic compounds and secondary organic aerosol pollution in different functional areas of petrochemical industrial cities in Northwest China

      2023, Science of the Total Environment
      Citation Excerpt :

      This can alter the light absorption and surface properties of particles. Aerosol time-of-flight mass spectrometry (ATOFMS) analysis revealed that the single scattering albedo (SSA) was directly correlated with the mixing state of the EC and OC particles (Tang et al., 2014). According to the analysis of the overall particle mixing state in Fig. 8, particles mixed with nitrate, sulfate ions and C2H3O+ (m/z = 43) widely existed in the different types of particles, especially nitrate, which suggests that particles experience different degrees of secondary reactions when entering the atmosphere from emission sources or during atmospheric transportation.

    • Morphology, composition, and sources of individual aerosol particles at a regional background site of the YRD, China

      2019, Journal of Environmental Sciences (China)
      Citation Excerpt :

      In the YRD, vehicle emissions and fossil fuel combustions emit high concentrations of SO2 and NO2, and that were contributed to large amounts of sulfate and nitrate (Geng et al., 2009). Several studies have been reported on aerosol characteristics in various urban regions of the YRD (Cao et al., 2009; Tie and Cao 2009; Deng et al., 2011; Kang et al., 2013; Tang et al., 2014; Wang et al., 2014); however, only a few studies have done in the background area of the YRD (Pan et al., 2010; Huang et al., 2011; Feng et al., 2015; Shen et al., 2015). Understanding the aerosol characteristics at the regional background site assist their source determination, thus indicating the heterogeneous reactions of long-range transported urban aerosols (Toscano et al., 2005).

    • An observational study of nitrous acid (HONO) in Shanghai, China: The aerosol impact on HONO formation during the haze episodes

      2018, Science of the Total Environment
      Citation Excerpt :

      The ozone density was measured by Total Ozone Mapping Spectrometer (http://toms.gsfc.nasa.gov/teacher/ozoneoverhead.html). The typical AOD, SSA and Alpha values during clean and pollution period were 0.66, 0.89, 1.07, and 1.32, 0.90, 1.30, respectively (Cheng et al., 2015; Xu et al., 2012; Lv et al., 2017; Lei et al., 2013; Tang et al., 2014). The daytime OH concentration was calculated by applying the method proposed by Rohrer and Berresheim (2006).

    • Real-time chemical characterization of atmospheric particulate matter in China: A review

      2017, Atmospheric Environment
      Citation Excerpt :

      Enhanced light absorption is largely due to the presence of BC, but light-absorbing organics may play a role as well. For instance, a negative correlation was found between the number fraction of PM containing aromatic components and the single-scattering albedo in a relatively clean period (Tang et al., 2014). In polluted Beijing in summer 2006, EC, ammonium sulfate and OAs were the major contributors to light extinction when the PM2.5 level was below 50 μg m−3, while ammonium sulfate and ammonium nitrate became more important than carbonaceous components when the PM2.5 concentration was above 100 μg m−3 (Jung et al., 2009b).

    View all citing articles on Scopus
    View full text