One-year study of airborne sugar compounds: Cross-interpretation with other chemical species and meteorological conditions

Highlights

• The daily evolution of 17 sugar compounds in atmospheric aerosol was studied in León.

• Mannosan and levoglucosan are linked with traffic and fossil fuel combustion markers.

• Precipitation can cause an increase in glucose, sucrose and arabitol concentrations.

• On rainy days, mannitol is a good tracer for Alternaria.

• Some sugar compounds are correlated with rain intensity, swept volume and drop size.

Abstract

The daily evolution of seventeen sugar compounds (seven saccharides, seven alcohol-saccharides and three anhydrosaccharides) in atmospheric aerosol samples collected between 9 March 2016 and 14 March 2017 was studied in León (Spain). The main links between the concentration of sugar compounds and various chemical species, pollen, fungal spores and meteorological conditions were investigated. The results showed that, in spring, when high levels of metabolic activity of the plants occur and temperatures increase, glucose, sucrose, 2-methyl-erithritol, mannitol, arabitol and inositol, are significantly correlated with airborne pollen concentrations. Between spring and autumn, Alternaria air concentrations are significantly correlated with temperatures, arabitol and sorbitol + adonitol concentrations. Furthermore, during rainy days, Alternaria is also correlated with mannitol. In autumn, lower temperatures cause an increase in the concentrations of levoglucosan, mannosan and galactosan, probably due to the increased use of domestic heating devices. These anhydrosugars and arabinose, fructose and glucose, are significantly correlated with K, NO₃⁻, EC, OC, Cu, Zn, Se, Pb, V and Ni, while mannosan also correlates with As, showing that these anhydrosaccharides can be emitted from different anthropogenic sources. Precipitation causes an increase in glucose and sucrose concentrations, due to the break of pollen particles that produce hundreds of fine size particles. Besides, precipitation causes an increase in arabitol concentrations, due to the release and growth of fungi.

Introduction

Atmospheric bioaerosols comprise a variety of biological particles that include bacteria, fungi, fungal spores, pollen and allergenic pollens, arthropod allergens (e.g., from mites and cockroaches), pet allergens, algae, amoebae and viruses (Després et al., 2012; Douwes et al., 2008; Fröhlich-Nowoisky et al., 2016). They play an important role in human health and atmospheric processes. Pollen allergens are considered to be primarily glycoproteins that are released into the atmosphere in the form of exudates. Thus, it is the glucidic fraction that triggers the allergic responses, so an interaction of sugars with other particles, biotic or not, can clearly increase the symptoms of respiratory allergies (Dall'Antonia et al., 2014). The presence of high levels of pollen in the atmosphere has been related to allergic respiratory diseases, such as asthma, rhinitis and atopic dermatitis (D'Amato et al., 2007; Fröhlich-Nowoisky et al., 2016; Fukutomi and Taniguchi, 2015). In particular, among fungal spores, Alternaria alternata can be considered one of the most allergenic species. The main allergen produced by this fungal spore is the Alt a 1 acid glycoprotein (16.4 kDa and 15.3 kDa band), which is found in the cytoplasm and cellular wall of mould and mycelial spores. It is related to the development of asthma and rhinitis, as well as to epidemics of asthma exacerbation (Armentia et al., 2019; Fukutomi and Taniguchi, 2015), although its true biological function remains unknown.

Sugar compounds (saccharides, alcohol-saccharides and anhydrosaccharides) represent an important part of the water-soluble organic fraction in the atmospheric aerosol (Barbaro et al., 2019; Burshtein et al., 2011; Simoneit et al., 2004; Wang et al., 2018; Yttri et al., 2007). These organic compounds can have their origin in different anthropogenic and natural sources, including biomass combustion and/or biogenic primary emissions (Table S1).

Dust storms have been reported to be a natural source of bioaerosols and sugar compounds such as arabitol, mannitol, sucrose and tehalose (found in many anhydrobiotic organisms), due to the resuspension of soil material and biogenic sources like pollen and fungal spores (Kumar et al., 2017; Oduber et al., 2020; Oduber et al., 2019b). Anhydrosaccharides, levoglucosan, galactosan and mannosan, which originate from the pyrolysis of cellulose and hemicellulose, and potassium, located in the cytoplasm of plant cells, are used as biomass burning tracers (Vicente and Alves, 2018). Arabitol and mannitol, responsible for the energy storage in fungi, have been pointed out as biomarkers of fungal spores in the air (Bauer et al., 2008; Burshtein et al., 2011; Medeiros et al., 2006). Nevertheless, high concentrations of alcohol-saccharides have also been observed in plant tissues. Mannitol is found in more than 70 different families of plants, as well as bacteria. Similarly, sorbitol is the primary photosynthetic metabolite of sucrose in many species, for example of the Rosaceae family, including all of the genus Malus, Pyrus and Prunus (apples, pears and stone fruits, respectively) (Dumschott et al., 2017). Sucrose, fructose and glucose are free sugars found in high concentrations in plant tissues and are major contributors to pollen (Fu et al., 2012; Medeiros et al., 2006; Simoneit et al., 2004; Speranza et al., 1997). Besides, a small fraction of fructose, glucose and other less studied saccharides, such as arabinose, galactose, xylose, xylitol and ribose, has been observed in smoke samples from biomass burning (Alves et al., 2011; Medeiros et al., 2006; Vicente et al., 2013).

The atmospheric concentrations of bioaerosols are also affected by meteorological conditions. Temperature, wind speed, relative humidity and precipitation are parameters that influence the airborne concentration of fungal spores, plants flowering and pollination periods (Fernández-González et al., 1993; Filali Ben Sidel et al., 2015; Grinn-Gofroń et al., 2019; Makra et al., 2014; Oduber et al., 2019a; Sabo et al., 2015). Although the impact of precipitation on different sugar compounds have not been examined in detail until now, to better understand atmospheric processes, it may be important to assess the behaviour of these constituents after a rain event. For example, the below-cloud scavenging (BCS) process has a direct impact on the aerosol concentration in the air (i.e. Blanco-Alegre et al., 2018; Castro et al., 2010; Cugerone et al., 2018). This process depends on several features of rainfall, such as raindrop size distribution and rainfall rate, and on the local/regional concentration of the particles and gases in the atmosphere (Celle-Jeanton et al., 2009; Xu et al., 2017). The scavenging of different species, mainly inorganic, and the relationship with the intensity and volume of precipitation, has been studied by several authors in different regions of the world (i.e. Blanco-Alegre et al., 2019; Calvo et al., 2012; Custódio et al., 2014; Pan and Wang, 2015; Uchiyama et al., 2017). Even though a washing effect by rain has been observed for several aerosols, certain particles as pollen can swell and rupture producing hundreds of fine-size particles (D'Amato et al., 2007), increasing the concentration of sugar compounds in the atmosphere.

It is important to know under what meteorological conditions sugar compounds are emitted and what chemical and biological markers are well correlated with them. This will allow to determine the natural and/or anthropogenic origin of these compounds. This type of studies is only possible if a long-term study is carried out, considering the meteorological parameters, chemical composition and biogenic contribution of atmospheric particles. Thus, this study aims to: i) evaluate, between March 2016 and March 2017 in León (Spain), the daily and seasonal evolution of seventeen sugar compounds in the PM₁₀ fraction: arabinose, fructose, galactose, glucose, ribose, sucrose, xylose, adonitol, arabitol, 2-methyleryritol, myoinositol, mannitol, sorbitol, xylitol, galactosan, levoglucosan and mannosan; ii) establish the correlation with meteorological parameters, with some biological markers (pollen and fungal spore concentrations) and with chemical markers (K, As, Se, SO₄²⁻, NO₃⁻, Pb, Zn, etc.); iii) finally, estimate the impact of precipitation on the concentration of sugar compounds.

To our knowledge, only a few studies have evaluated the temporal evolution of the main sugar compounds in particulate matter and much less have related their concentrations in the environment to meteorological conditions, mainly under rainy weather, to some biological tracers and to other chemical species.