Role of sea salt aerosols in the formation of aromatic secondary organic aerosol: yields and hygroscopic properties

Engling

et al. 2015

Environ. Res. Lett.

Fungal spores are ubiquitous in the Earth's atmosphere, especially in the environment of tropical rainforests with intense biological activities. To assess the impact of fungi on chemical components of atmospheric aerosols at a Chinese tropical rainforest site, size-segregated fungal spore tracers (i.e. arabitol and mannitol) were measured along with major aerosol components, including carbonaceous species and water-soluble inorganic ions. The fungal spore tracers were found to be predominately associated with coarse particles, in which organic carbon (OC) and potassium (K + ) were also present at significant levels. Enhanced amounts of fungal spore tracers were closely linked to rainfall events. Moreover, fungal spore tracers exhibited positive correlations with relative humidity and negative correlations with wind speed, temperature or radiation. The relationships between fungal spore tracers and meteorological factors are consistent with the emission features of actively discharged fungal spores, which are generally associated with sugar alcohols and by-products such as the inorganic ion K + . The excellent correlations between fungal spore tracers and OC or K + in the coarse particles further suggested their common emission sources. Absolute principal factor analysis further identified fungi as the largest contributor to coarse OC and K + (both at ∼66%) in this rainforest.

Section: Contributions Of Fungi To Coarse Carbonaceous and Potassium mentioning

confidence: 99%

Significant influence of fungi on coarse carbonaceous and potassium aerosols in a tropical rainforest

Engling

et al. 2015

Environ. Res. Lett.

“…ATD contains hygroscopic inorganic salts that form the thin water film on the surface of ATD particles when the salts are deliquescent (or above ERH). Some salts such as magnesium sulfate and calcium sulfate can be hydrated even at low humidity (Beardsley et al, 2013;Jang et al, 2010). Gustafsson et al (2005) reported that ATD particles showed a substantially high affinity to water compared to pure CaCO 3 particles.…”

Section: Gas-dust Particle Partitioningmentioning

confidence: 99%

Modeling atmospheric mineral aerosol chemistry to predict heterogeneous photooxidation of SO<sub>2</sub>

Jang

Park

2017

Atmos. Chem. Phys.

Self Cite

Abstract. The photocatalytic ability of airborne mineral dust particles is known to heterogeneously promote SO 2 oxidation, but prediction of this phenomenon is not fully taken into account by current models. In this study, the Atmospheric Mineral Aerosol Reaction (AMAR) model was developed to capture the influence of air-suspended mineral dust particles on sulfate formation in various environments. In the model, SO 2 oxidation proceeds in three phases including the gas phase, the inorganic-salted aqueous phase (non-dust phase), and the dust phase. Dust chemistry is described as the absorption-desorption kinetics of SO 2 and NO x (partitioning between the gas phase and the multilayer coated dust). The reaction of absorbed SO 2 on dust particles occurs via two major paths: autoxidation of SO 2 in open air and photocatalytic mechanisms under UV light. The kinetic mechanism of autoxidation was first leveraged using controlled indoor chamber data in the presence of Arizona Test Dust (ATD) particles without UV light, and then extended to photochemistry. With UV light, SO 2 photooxidation was promoted by surface oxidants (OH radicals) that are generated via the photocatalysis of semiconducting metal oxides (electron-hole theory) of ATD particles. This photocatalytic rate constant was derived from the integration of the combinational product of the dust absorbance spectrum and wave-dependent actinic flux for the full range of wavelengths of the light source. The predicted concentrations of sulfate and nitrate using the AMAR model agreed well with outdoor chamber data that were produced under natural sunlight. For seven consecutive hours of photooxidation of SO 2 in an outdoor chamber, dust chemistry at the low NO x level was attributed to 55 % of total sulfate (56 ppb SO 2 , 290 µg m −3 ATD, and NO x less than 5 ppb). At high NO x (> 50 ppb of NO x with low hydrocarbons), sulfate formation was also greatly promoted by dust chemistry, but it was suppressed by the competition between NO 2 and SO 2 , which both consume the dust-surface oxidants (OH radicals or ozone).

“…Moreover, the further reactive uptake of N 2 O 5 was reported to be dependent on the chloride to nitrate ratio of the reacted SSAs and their phases . The primary and secondary organics, biogenic particulates, sea-salt sulfates (ss-SO 2− 4 ), non-sea-salt sulfates (nss-SO 2− 4 ), etc., add greater complexity to these SSAs (O'Dowd and de Leeuw, 2007;Keene et al, 2007;Prather et al, 2013;Beardsley et al, 2013;Ault et al, 2013b). A detailed knowledge of the hygroscopic properties, mixing states, and the spatial distribution of the chemical components in NaClNaNO 3 mixture particles, as partially or fully reacted SSA surrogates, can serve as a good preliminary step to a better understanding of the complex chemical/physical mixing states, hygroscopic behavior, and reactivity of ambient SSAs.…”

Section: Gupta Et Al: Hygroscopic Properties Of Nacl and Nano 3 Mmentioning

confidence: 99%

“…Although real ambient SSAs are complex mixtures containing NaCl, other inorganic salts, and organics (O'Dowd and de Leeuw, 2007;Keene et al, 2007;Prather et al, 2013;Beardsley et al, 2013;Ault et al, 2013b), NaCl particles have been studied as genuine SSA surrogates in many laboratories (Martin, 2000;Krieger et al, 2012). Based on the experimental phase diagrams of deliquescence and efflorescence for the NaCl-NaNO 3 system (Figs.…”

Section: Atmospheric Chemistrymentioning

confidence: 99%

Hygroscopic properties of NaCl and NaNO<sub>3</sub> mixture particles as reacted inorganic sea-salt aerosol surrogates

et al. 2015

Abstract. NaCl in fresh sea-salt aerosol (SSA) particles can partially or fully react with atmospheric NO x /HNO 3 , so internally mixed NaCl and NaNO 3 aerosol particles can co-exist over a wide range of mixing ratios. Laboratorygenerated, micrometer-sized NaCl and NaNO 3 mixture particles at 10 mixing ratios (mole fractions of NaCl (X NaCl ) = 0.1 to 0.9) were examined systematically to observe their hygroscopic behavior, derive experimental phase diagrams for deliquescence and efflorescence, and understand the efflorescence mechanism. During the humidifying process, aerosol particles with the eutonic composition (X NaCl = 0.38) showed only one phase transition at their mutual deliquescence relative humidity (MDRH) of 67.9 (±0.5) %. On the other hand, particles with other mixing ratios showed two distinct deliquescence transitions; i.e., the eutonic component dissolved at MDRH, and the remainder in the solid phase dissolved completely at their DRHs depending on the mixing ratios, resulting in a phase diagram composed of four different phases, as predicted thermodynamically. During the dehydration process, NaCl-rich particles (X NaCl > 0.38) showed a two stage efflorescence transition: the first stage was purely driven by the homogeneous nucleation of NaCl and the second stage at the mutual efflorescence RH (MERH) of the eutonic components, with values in the range of 30.0-35.5 %. Interestingly, aerosol particles with the eutonic composition (X NaCl = 0.38) also showed two-stage efflorescence, with NaCl crystallizing first followed by heterogeneous nucleation of the remaining NaNO 3 on the NaCl seeds. NaNO 3 -rich particles (X NaCl ≤ 0.3) underwent singlestage efflorescence transitions at ERHs progressively lower than the MERH because of the homogeneous nucleation of NaCl and the almost simultaneous heterogeneous nucleation of NaNO 3 on the NaCl seeds. SEM/EDX elemental mapping indicated that the effloresced NaCl-NaNO 3 particles at all mixing ratios were composed of a homogeneously crystallized NaCl moiety in the center, surrounded either by the eutonic component (for X NaCl > 0.38) or NaNO 3 (for X NaCl ≤ 0.38). During the humidifying or dehydration process, the amount of eutonic composed part drives particle/droplet growth or shrinkage at the MDRH or MERH (second ERH), respectively, and the amount of pure salts (NaCl or NaNO 3 in NaCl-or NaNO 3 -rich particles, respectively) drives the second DRHs or first ERHs, respectively. Therefore, their behavior can be a precursor to the optical properties and direct radiative forcing for these atmospherically relevant mixture particles representing the coarse, reacted inorganic SSAs. In addition, the NaCl-NaNO 3 mixture aerosol particles can maintain an aqueous phase over a wider RH range than pure NaCl particles as SSA surrogate, making their heterogeneous chemistry more probable.