Elsevier

Atmospheric Environment

Volume 128, March 2016, Pages 227-234
Atmospheric Environment

Impacts of crystal metal on secondary aliphatic amine aerosol formation during dust storm episodes in Beijing

https://doi.org/10.1016/j.atmosenv.2016.01.013Get rights and content

Highlights

  • We detected the trimethylamine-N-oxide in fine particle matter in Beijing.

  • Trimethylamine-N-oxide concentration was highly associated with Al.

  • We applied the DFT method to investigate the formation mechanism of TMAO.

Abstract

Trimethylamine (TMA) enters the atmosphere from a variety of sources and is a ubiquitous atmospheric organic base. The atmospheric reaction mechanism of TMA with key atmospheric oxidants is important to predict its distribution and environmental behavior in the particle phase. While previous studies have extensively focused on the production of particle amine salts (i.e. trimethylamine-N-oxide (TMAO)) using chamber experiments, the atmospheric behavior of TMAO in the environment is still poorly understood. Ambient fine particulate matter (PM2.5) was collected at two sampling sites in Beijing from March 10 to May 10, 2012. We analyzed the samples for water-soluble ions, crystal metals, TMA, and TMAO. Water-soluble ions (e.g. SO42, NO3, NH4+), TMA, and TMAO were measured using ion chromatography, while crystal metal (e.g. Al, Fe, Mn) in PM2.5 was quantified by inductively coupled plasma mass spectrometry (ICP-MS). Two dust storms (DS) occurred during the sampling period on March 28 and April 28. Mineral dust impacted PM2.5 mass and composition greatly during dust storm days, as it contributed approximately 1.2–4.0 times greater on dust storm days versus non-dust storm days. We found TMAO concentrations were highly associated with aluminum in PM2.5. Further, we applied the density functional theory (DFT) method to confirm that aluminum plays a catalytic effect in the reaction of TMA with ozone (O3). Our work improves understanding of the effect of crystal metals on secondary aliphatic amine aerosol formation in the atmosphere.

Introduction

Among the organic compounds relevant in the atmosphere, amines are unique in their acid-neutralizing capability (Silva et al., 2008). Amines are derivatives of ammonia in which an alkyl or aryl group has replaced at least one hydrogen atom (Ge et al., 2011a, Ge et al., 2011b). Much attention has been devoted to the environmental behavior of low-molecular weight amines, such as dimethylamine (DMA) and trimethylamine (TMA) (Ge et al., 2011a, Ge et al., 2011b). Schade and Crutzen (1995) estimated that TMA was the greatest contributor of amines to the global input of nitrogen from animal husbandry. TMA can be a strong base even in the presence of ammonia, with concentrations as much as 20% of the volume of ammonia, and it is even more important than ammonia in enhancing atmospheric nucleation (Tang et al., 2014). Further, TMA can also participate in the formation of secondary organic aerosol. Several studies have shown that gas-phase TMA can form non-salt organic aerosol products through reactions with oxidizing agents such as O3, OH, and NO3 radicals (Erupe et al., 2010, Murphy et al., 2007, Silva et al., 2008, Tang et al., 2013, Price et al., 2014). Trimethylamine-N-oxide (TMAO) has been confirmed as the reaction product of TMA in several smog chamber studies using aerosol time-of-flight mass spectrometry (ATOFMS) (Erupe et al., 2010, Murphy et al., 2007, Zhang et al., 2012). However, the concentration and environmental particle behavior of TMAO in different regions is still unclear.

Asian dust (yellow sand) storms commonly originate from arid areas in China and Mongolia, where strong surface winds uplift mineral particles into the middle troposphere (Liu et al., 2014a, Liu et al., 2014b, Gross et al., 2015). Springtime trade winds carry a portion of this dust across China's mainland to East Asia and North America, which increases ambient particulate matter (PM) concentrations (Cao et al., 2015). According to a number of studies, the chemical characteristics of the dust involved in storm events is responsible for the feedback effects on climate and human health during periods of increased PM concentration (Wang et al., 2011, Srivastava et al., 2014, Liu et al., 2014a, Zhang et al., 2010). The heterogeneous reactions that occur on the large surface area of dust particles alter radioactive transfer and rates of photolysis (Manktelow et al., 2010, Sullivan et al., 2007, Erel et al., 2006). Mineral dust particles can become internally mixed with secondary species such as ammonium sulfate, ammonium nitrate, hydrochloric acid, sea salt, and particles produced by biomass burning through coagulation, cloud processing, and heterogeneous reactions (Usher et al., 2003). Mineral dust mixed with secondary acids can increase the solubility and bioavailability of iron, which is an important pathway for the fertilization of remote oceans with subsequent climate impacts (Shi et al., 2011). Nitrate on dust particle is also an important vector for nitrogen fertilization of oceans (Wang et al., 2013, Manktelow et al., 2010, Zhang et al., 2010). Aluminum is a major component of mineral dust in the atmosphere (Zhang et al., 2003, Zhang et al., 2010). Input fluxes of dissolved dust aluminum from the Gobi desert region could result in phytoplankton blooms in the Southern Yellow Sea of China (Ren et al., 2011). Furthermore, several chamber experiments have confirmed that the presence of aluminum on dust particles could enhance the photo-oxidation rates of SO2, NO2, α-pinene, and m-xylene, resulting in the significant increases in secondary aerosol formation (Liu et al., 2013, Loza et al., 2012, Ma et al., 2008, Kroll and Seinfeld, 2008), which is one of the largest contributors to ambient PM during haze episodes in China (Huang et al., 2014, Liu et al., 2016). Currently, several quantum models, including density functional theory (DFT) (Xu et al., 2010; Zhang et al., 2014) and master chemical mechanism (MCM) (Wang et al., 2015), have been used to predict the chemical compositions of gas-phase oxidation products in the atmosphere, as those observed by the chamber experiments (Xu et al., 2010; Zhang et al., 2014, Wang et al., 2015). These models can provide more detail about the thermodynamic and kinetic analyses for oxidative reactions, but they require much less experimental effort (Xu et al., 2005; Zhang et al., 2014). Because DFT has computational advantages, it has successfully been used to study atmospheric reactions such as secondary formation of polycyclic aromatic hydrocarbons (PAHs) (Zhang et al., 2014) and dioxin formation from phenoxy radicals with 2-chlorophenoxy radicals (Xu et al., 2010).

We collected 24-h ambient PM2.5 samples during dust storm episodes at two sampling sites in Beijing, and measured their TMAO concentrations. We also combined experimental and DFT methods to confirm the secondary formation reaction of TMA on particles. This study provides new information to increase understanding of the factors that control secondary aliphatic amine aerosol formation in the atmosphere.

Section snippets

Aerosol samplings

The sampling site S1 (latitude: N 39°97′91″0; longitude: E116°21′30″0) was located on the roof of an office building 20 m above ground within an urban area at the Institute of Botany of the Chinese Academy of Sciences. The site was 30 km away from the city center, it was surrounded by unused land, and the nearest source of anthropogenic pollution was a lightly trafficked road about 500 m away. The sampling site S2 was located near a busy traffic line (latitude: N 39°56′50″7; longitude:

Results

Two dust storm (DS) events occurred during the sampling period on March 28 and April 28. The storms spread over an area that encompassed both sampling sites S1 and S2. Lead isotopes, 24-h backward trajectories, and meteorological factors (e.g. temperature, relative humidity, wind speed) were used to confirm the dust storm events and origins, which were described in detail in previous work (Liu et al., 2014b). During the sampling period, PM2.5 mass peaked at 409 μg m−3 at the peri-urban site (S1

Discussion

We assessed the relationships between TMAO concentration and PM2.5 components at the two sampling sites using Pearson's correlation. We found moderate to strong correlations between increased TMAO concentration and sulfate/nitrate (S1: r = 0.528–0.629, p < 0.001; S2 = 0.370–0.436, p < 0.001), which is consistent with the previous finding that nitrate and sulfate formation is highly associated with amine-containing particles (Figs. S10, S11 and Table S2) (Zhang et al., 2012). TMAO concentration

Conclusions

To the best of our knowledge, this study is the first to detect trimethylamine-N-oxide in ambient particle samples and assess the catalytic effects of metals on its formation mechanism during dust storm episodes. We found that significantly higher TMAO in dust particles was strongly associated with increased levels of sulfate, nitrate, and aluminum. The experimental and DFT results indicate that aluminum plays an important role in TMAO formation in the real atmospheric environment. Our results

Acknowledgments

This research was supported by the Natural National Science Foundation of China (No. 41305110). We would like to thank Ms. Abigail Rogerson from University of Wisconsin–Madison for her assistance on polishing up the article.

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