The impact of ammonium on the distillation of organic carbon in PM2.5

https://doi.org/10.1016/j.scitotenv.2021.150012Get rights and content

Highlights

  • OC fractions shift from low to high desorption temperature during pollution cycles.

  • Matrix effects lead to redistribution of OC fractions during thermal desorption.

  • Ammonium salts contribute to the observed matrix effects of OC redistribution.

Abstract

Thermal desorption coupled with different detectors is an important analysis method for ambient carbonaceous aerosols. However, it is unclear how the compounds coexisting in both the gas and particle phases affect carbonaceous aerosol concentrations and measurements during thermal desorption. We observed matrix effects leading to a redistribution of different OC fractions (OC1 to OC4) during the thermal desorption process. These factors led to the formation of OC with low volatility (OC4), mainly from high-volatility OC (OC1 and OC2). Laboratory studies further indicated that ammonium promotes such matrix effects by transforming OC in the particle phase. Therefore, in addition to providing insights into the chemical evolution of OC during haze events, we argue that thermal-desorption-based OC measurements should be used with caution, which is an important step towards a more accurate measurement of OC in the ambient atmosphere.

Introduction

Carbonaceous aerosols are an important component (20–50%) of ambient particulate matter (PM) (Cao et al., 2007; Han et al., 2016; Kanakidou et al., 2005; Putaud et al., 2010) and have attracted considerable attention among atmospheric environment researchers due to their crucial effects on air quality, climate change, and human health (Bikkina et al., 2016; Bond et al., 2013; Cao et al., 2004; Watson, 2002; Zhang et al., 2008). Organic carbon (OC), which is formed by both direct emissions (namely, primary organic carbon, POC), including biomass burning, fossil fuel combustion, vehicle exhaust, plant material, soil and dust suspension, and secondary formation from the oxidation of volatile organic compounds (VOCs) or POC in the atmosphere (Han et al., 2008; Pio et al., 2011; Turpin and Huntzicker, 1995), is the important contributor to carbonaceous aerosols. To date, thousands of organic compounds, including alkanes, polycyclic aromatic hydrocarbons (PAHs), hopanes, steranes, and esters, have been identified in OC (Mauderly and Chow, 2008; Ruiz-Jimenez et al., 2011). However, the identified molecules contribute less 30% of the total OC mass in PM2.5 (Aiken et al., 2008; Alier et al., 2013; Goldstein et al., 2008; Hallquist et al., 2009; Yang et al., 2020), even though many sophisticated techniques, such as thermal desorption aerosol gas chromatography mass spectrometry (TAG-GC–MS) (Goldstein et al., 2008), thermodenuder Aerosol Mass Spectrometer (TD-AMS) (Huffman et al., 2009; Lee et al., 2010), two-dimensional gas chromatography (GC × GC) (Liu and Phillips, 1991) and liquid chromatography electrospray ionization orbitrap (LC-ESI-Orbitrap) (Wang et al., 2017), have been developed. Since acquiring complete compositional information regarding OC remains a long-standing challenge in OC measurement, analytical technologies based on the bulk properties of OC, such as thermal desorption-based methods, are still useful and widely used for OC measurements.

In thermal desorption-based technologies, such as TAG-GC–MS (Williams et al., 2006), Filter Inlet for Gases and AEROsols (FIGAERO) (Lopez-Hilfiker et al., 2014) and OC/EC analysis, PM is first collected on a substrate, and then the desorbed components or oxidation products are detected at a fixed or programmed temperature. OC and EC can be further thermally classified into eight fractions based on desorption temperature during OC/EC analysis, i.e., four OC fractions (OC1, OC2, OC3, and OC4 in a He atmosphere), a pyrolyzed carbon fraction (PyOC, determined when the laser light attained its original intensity after O2 was added), and three EC fractions (EC1, EC2, and EC3 in a 2% O2/98% He atmosphere) (Chen et al., 2017; Zhang et al., 2018). The source of carbonaceous aerosols can be further analyzed based on the distribution of these distillates because of the specific OC/EC ratio and/or the characteristic distribution of the distillates from a given source (Chow et al., 2004; Hwang and Hopke, 2007; Watson et al., 2005). For example, the OC/EC ratios in samples obtained from coal combustion, automobile exhaust, and biomass combustion were 12.0, 4.1, and 60.3, respectively (Cao et al., 2005; Wang et al., 2018). Sources of carbonaceous aerosols including gasoline/diesel vehicle exhaust, coal combustion, biomass burning, and specific diesel vehicle exhaust were apportioned based on Positive Matrix Factorization (PMF) analysis of OC components in Haikou, China (Liu et al., 2018). In addition, the single carbonaceous thermal distribution (CTD) from the converted CO2 can also be used to understand the source and chemical composition of carbonaceous aerosols (Bae et al., 2019; Bae et al., 2014).

It should be noted that PM2.5 is a mixture of organics and inorganics in which carbonaceous carbon coexists with the matrix of other components. It has been recognized that some inorganic salts can promote the formation of secondary organic aerosol (SOA) and influence the volatility of OA through heterogeneous reactions (Ervens et al., 2011; Faust et al., 2017; Ortiz-Montalvo et al., 2014). During EC/OC analysis, Yu et al. (2002) observed enhancement of charring of cellulose and starch when they were mixed with ammonium bisulfate, which was explained by the promotion of dehydration reactions through acid catalysis. It has also been demonstrated that inorganic compounds found indigenously within biomass can promote the formation of char (Sekiguchi and Shafizadeh, 1984). On the other hand, several studies have found that the presence of NaCl (Kirchstetter and Novakov, 2007) and metal salts (Wang et al., 2010) can reduce the combustion temperature of EC. Despite these insights, it is still unclear how inorganic salts affect the distribution of OC1–OC4 in ambient particles during OC/EC analysis. In particular, the concentration of PM2.5, as well as that of sulfate, declined substantially in most regions of China (Li et al., 2020; Wang et al., 2020) after the central government executed the Air Pollution Prevention and Control Action Plan in September 2013, while the ammonium and nitrate fractions in PM2.5 increased (Xu et al., 2019). Therefore, it is vital to understand the interaction between inorganic components and OC in PM2.5. In this study, observations of OC in downtown Beijing were performed by an OC/EC analyzer (Model-4, Sunset Lab. Inc.) based on the thermal-optical method. The influences of chloride, nitrate, sulfate, and ammonium (measured by a time-of-flight aerosol chemical speciation monitor, ToF-ACSM, Aerodyne Co. Ltd., USA) on the distribution of OC distillates are discussed. This work will help us understand both the evolution of the PM2.5 composition at different pollution levels and the effect of the inorganic matrix on thermal-desorption-based OC measurements.

Section snippets

Field measurements

Ground-based observations were performed at the Aerosol and Haze Laboratory/Beijing University of Chemical Technology Station (AHL/BUCT Station) (Lat. 39°56′31″ and Lon. 116°17′52″) from September 1, 2020 to November 31, 2020 in downtown Beijing, China. The details of the station were described in our previous work (Chu et al., 2021; Liu et al., 2020; Zhou et al., 2019). The instruments used in this work are shown in Table S1.

The OC and EC concentrations were determined semi-continuously using

Dependence of OC distillates on the pollution level

OC1–OC4 represent carbonaceous components distilled at different temperatures (Bae et al., 2004). Five overlapping peaks (from Peak 1 to Peak 5 in Figs. 1 and S4, due to the shorter analysis time of the NIOSH protocol (Wu et al., 2016)) were observed in the typical desorption curve (analysis lapse time of 1–400 s). Peak fitting was conducted to identify peak positions (Fig. S4) and quantify these components. Peak 5 was mainly located in the EC region and remained very stable in terms of both

Conclusions

Our results demonstrate that OC fractions showed slightly transition from low volatile to high volatile during pollution cycles. Moreover, a matrix effect that can lead to redistribution of different OC fractions during thermal desorption process was observed. These factors led to the increased of low volatile OC fractions (OC4). Laboratory studies further supported the assumption that ammonium plays a key role in the redistribution of OC. Therefore, in addition to providing insights into the

CRediT authorship contribution statement

Zemin Feng: Writing - original draft, Conducting experiments, Data curation. Feixue Zheng: Investigation, Data curation. Chao Yan: Investigation, Data curation. Peng Fu: Investigation, Data curation. Yusheng Zhang: Investigation, Data curation. Zhuohui Lin: Investigation, Data curation. Jing Cai: Investigation, Data curation. Wei Du: Investigation, Data curation. Yonghong Wang: Investigation, Data curation. Juha Kangasluoma: Investigation, Data curation. Federico Bianchi: Investigation, Data

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This research was financially supported by the National Natural Science Foundation of China (41877306, 92044301), the Ministry of Science and Technology of the People's Republic of China (2019YFC0214701), the Academy of Finland via the Center of Excellence in Atmospheric Sciences (272041, 316114, and 315203) and the European Research Council via ATM-GTP 266 (742206) and ERA-PLANET (www.era-planet.eu) transnational project SMURBS (www.smurbs.eu) (grant agreement no. 689443), funded under the EU

References (80)

  • T.W. Kirchstetter et al.

    Controlled generation of black carbon particles from a diffusion flame and applications in evaluating black carbon measurement methods

    Atmos. Environ.

    (2007)
  • X. Li et al.

    Responses of gaseous sulfuric acid and particulate sulfate to reduced SO2 concentration: a perspective from long-term measurements in Beijing

    Sci. Total Environ.

    (2020)
  • B. Liu et al.

    Characteristics and sources of the fine carbonaceous aerosols in Haikou, China

    Atmos. Res.

    (2018)
  • C. Pio et al.

    OC/EC ratio observations in Europe: re-thinking the approach for apportionment between primary and secondary organic carbon

    Atmos. Environ.

    (2011)
  • J.P. Putaud et al.

    A european aerosol phenomenology – 3: physical and chemical characteristics of particulate matter from 60 rural, urban, and kerbside sites across Europe

    Atmos. Environ.

    (2010)
  • M. Statheropoulos et al.

    Quantitative thermogravimetric-mass spectrometric analysis for monitoring the effects of fire retardants on cellulose pyrolysis

    Anal. Chim. Acta

    (2000)
  • X. Tang et al.

    Speciation of the major inorganic salts in atmospheric aerosols of Beijing, China: measurements and comparison with model

    Atmos. Environ.

    (2016)
  • B.J. Turpin et al.

    Identification of secondary organic aerosol episodes and quantitation of primary and secondary organic aerosol concentrations during SCAQS

    Atmos. Environ.

    (1995)
  • Q. Xu et al.

    Nitrate dominates the chemical composition of PM2.5 during haze event in Beijing, China

    Sci. Total Environ.

    (2019)
  • S. Yang et al.

    Characteristics and seasonal variations of high-molecular-weight oligomers in urban haze aerosols

    Sci. Total Environ.

    (2020)
  • J. Zhang et al.

    Seasonal variation and size distributions of water-soluble inorganic ions and carbonaceous aerosols at a coastal site in Ningbo, China

    Sci. Total Environ.

    (2018)
  • X. Zhang et al.

    Pollution sources of atmospheric fine particles and secondary aerosol characteristics in Beijing

    J. Environ. Sci.

    (2020)
  • A.C. Aiken et al.

    O/C and OM/OC ratios of primary, secondary, and ambient organic aerosols with high-resolution time-of-flight aerosol mass spectrometry

    Environ. Sci. Technol.

    (2008)
  • P.K. Aiona et al.

    A role for 2-methyl pyrrole in the Browning of 4-oxopentanal and limonene secondary organic aerosol

    Environ. Sci. Technol.

    (2017)
  • M. Alier et al.

    Source apportionment of submicron organic aerosol at an urban background and a road site in Barcelona (Spain) during SAPUSS

    Atmos. Chem. Phys.

    (2013)
  • S. Bikkina et al.

    Dual carbon isotope characterization of total organic carbon in wintertime carbonaceous aerosols from northern India

    J. Geophys. Res. Atmos.

    (2016)
  • M.E. Birch et al.

    Elemental carbon-based method for monitoring occupational exposures to particulate diesel exhaust

    Aerosol Sci. Technol.

    (1996)
  • T.C. Bond et al.

    Bounding the role of black carbon in the climate system: a scientific assessment

    J. Geophys. Res. Atmos.

    (2013)
  • J. Cai et al.

    Size-segregated particle number and mass concentrations from different emission sources in urban Beijing

    Atmos. Chem. Phys.

    (2020)
  • M.R. Canagaratna et al.

    Elemental ratio measurements of organic compounds using aerosol mass spectrometry: characterization, improved calibration, and implications

    Atmos. Chem. Phys.

    (2015)
  • F. Canonaco et al.

    SoFi, an IGOR-based interface for the efficient use of the generalized multilinear engine (ME-2) for the source apportionment: ME-2 application to aerosol mass spectrometer data

    Atmos. Meas. Tech.

    (2013)
  • J.J. Cao et al.

    Characterization and source apportionment of atmospheric organic and elemental carbon during fall and winter of 2003 in Xi'an, China

    Atmos. Chem. Phys.

    (2005)
  • J.J. Cao et al.

    Spatial and seasonal distributions of carbonaceous aerosols over China

    J. Geophys. Res.

    (2007)
  • Q. Chen et al.

    Structural and light-absorption characteristics of complex water-insoluble organic mixtures in urban submicrometer aerosols

    Environ. Sci. Technol.

    (2017)
  • Y. Chen et al.

    Simultaneous measurements of urban and rural particles in Beijing – part 2: case studies of haze events and regional transport

    Atmos. Chem. Phys.

    (2020)
  • J.C. Chow et al.

    Equivalence of elemental carbon by thermal/optical reflectance and transmittance with different temperature protocols

    Environ. Sci. Technol.

    (2004)
  • K.R. Daellenbach et al.

    Characterization and source apportionment of organic aerosol using offline aerosol mass spectrometry

    Atmos. Meas. Tech.

    (2016)
  • B. Ervens et al.

    Secondary organic aerosol formation in cloud droplets and aqueous particles (aqSOA): a review of laboratory, field and model studies

    Atmos. Chem. Phys.

    (2011)
  • J.A. Faust et al.

    Role of aerosol liquid water in secondary organic aerosol formation from volatile organic compounds

    Environ. Sci. Technol.

    (2017)
  • G. Feick et al.

    On the thermal decomposition of ammonium nitrate. Steady-state reaction temperatures and reaction rate

    J. Am. Chem. Soc.

    (1954)
  • Cited by (2)

    • Is the key-treatment-in-key-areas approach in air pollution control policy effective? Evidence from the action plan for air pollution prevention and control in China

      2022, Science of the Total Environment
      Citation Excerpt :

      Jiang et al. (2020) also put forward that the main emission source of PM2.5 and PM10 is dust, and it involves industrial processes for VOCs and CO. OC is an important contributor to carbonaceous aerosols (Feng et al., 2022). Carbonaceous aerosols are an important component (20–50 %) of ambient particulate matter (PM) (Han et al., 2016).

    View full text