Chemical composition, microstructure, and hygroscopic properties of aerosol particles at the Zotino Tall Tower Observatory (ZOTTO), Siberia, during a summer campaign

Abstract

In this study we describe the hygroscopic properties of accumulation-and coarse-mode aerosol particles sampled at the Zotino Tall Tower Observatory (ZOTTO) in central Siberia (61 degrees N, 89 degrees E) from 16 to 21 June 2013. The hygroscopic growth measurements were supplemented with chemical analyses of the samples, including inorganic ions and organic/elemental carbon. In addition, the microstructure and chemical compositions of aerosol particles were analyzed by x-ray micro-spectroscopy (STXM-NEXAFS) and transmission electron microscopy (TEM). A mass closure analysis indicates that organic carbon accounted for 61 and 38% of particulate matter (PM) in the accumulation mode and coarse mode, respectively. The water-soluble fraction of organic matter was estimated to be 52 and 8% of PM in these modes. Sulfate, predominantly in the form of ammoniated sulfate, was the dominant inorganic component in both size modes: similar to 34% in the accumulation mode vs. similar to 47% in the coarse mode. The hygroscopic growth measurements were conducted with a filter-based differential hygroscopicity analyzer (FDHA) over the range of 5-99.4% RH in the hydration and dehydration operation modes. The FDHA study indicates that both accumulation and coarse modes exhibit pronounced water uptake approximately at the same relative humidity (RH), starting at similar to 70 %, while efflorescence occurred at different humidities, i.e., at similar to 35% RH for submicron particles vs. similar to 50% RH for supermicron particles. This similar to 15% RH difference was attributed to higher content of organic material in the submicron particles, which suppresses water release in the dehydration experiments. The kappa mass interaction model (KIM) was applied to characterize and parameterize non-ideal solution behavior and concentration-dependent water uptake by atmospheric aerosol samples in the 5-99.4% RH range. Based on KIM, the volume-based hygroscopicity parameter, kappa(v), was calculated. The kappa(v,ws) value related to the water-soluble (ws) fraction was estimated to be similar to 0.15 for the accumulation mode and similar to 0.36 for the coarse mode, respectively. The obtained kappa(v,ws) for the accumulation mode is in good agreement with earlier data reported for remote sites in the Amazon rain forest (kappa(v) approximate to 0.15) and a Colorado mountain forest (kappa(v) approximate to 0.16). We used the Zdanovskii-Stokes-Robinson (ZSR) mixing rule to predict the chemical composition dependent hygroscopicity, kappa(v,p). The obtained kappa(v,p) values overestimate the experimental FDHA-KIM-derived kappa(v,ws) by factors of 1.8 and 1.5 for the accumulation and coarse modes, respectively. This divergence can be explained by incomplete dissolution of the hygroscopic inorganic compounds resulting from kinetic limitations due to a sparingly soluble organic coating. The TEM and STXM-NEXAFS results indicate that aged submicron (> 300 nm) and supermicron aerosol particles possess core-shell structures with an inorganic core, and are en...

Long-term measurements (2010–2014) of carbonaceous aerosol and carbon monoxide at the Zotino Tall Tower Observatory (ZOTTO) in central Siberia

“…Our independent measurements performed from 15 to 25 December 2011 showed that the main inorganic anthropogenic ions are sulfates (∼ 32 %), nitrates (∼ 6 %), ammonium (∼ 5 %), and minor components such as sodium (∼ 1 %) and potassium (∼ 1 %). The contribution of other ions is less than 1 % (Mikhailov et al, 2015b).…”

“…A consequence of the atmospheric evolution of SOA is the convergence of its chemical composition and physical properties (Andreae, 2009). In particular, the CCN and hygroscopic properties of the SOA formed in the rain forest and boreal forest environments become very similar (Mikhailov et al, 2015b;Pöhlker et al, 2016).…”

“…In our analysis, we therefore differentiate between polluted, background, and clean periods. We refer to "background" conditions as an atmospheric state without the detectable influence of local or regional pollution sources but affected by emissions of natural origin as well as by pollution transported from very distant sources (Andreae, 2007;Chi et al, 2013;Mikhailov et al, 2015b). To define the concentrations of the measured species representing background air (or the other way around to define the polluted periods), we made use of a non-parametric statistical approach named REBS (robust extraction of background signal).…”

“…These compounds form secondary organic aerosols as a result of photochemical oxidation and gas-to-particle conversion (Hallquist et al, 2009). A substantial fraction of boreal forest organic aerosol consists of water-soluble compounds and therefore contributes to hygroscopic growth and cloud condensation nuclei (CCN) activity (Huff Hartz et al, 2005;Ehn et al, 2007;Carrico et al, 2008;Cerully et al, 2011;Jaatinen et al, 2014;Paramonov et al, 2013;Mikhailov et al, 2015b).…”

Mixing state and sources of submicron regional background aerosols in the northern Qinghai–Tibet Plateau and the influence of biomass burning

“…OC coatings on inorganic particles can induce an early deliquescence of particle surface compared to that of the pure inorganic compounds (Li et al, 2014a). Recently, Mikhailov et al (2015) found that the semi-solid state of the OC coating can lead to kinetic limitations of water uptake and release during hydration and dehydration cycles in the background area. OC dominated in fine particles, accounting for 43 % of mass on average, followed by sulfate (28 %) and nitrate (1 %) (Du et al, 2015).…”