Effect of Structural Heterogeneity in Chemical Composition on Online Single-Particle Mass Spectrometry Analysis of Sea Spray Aerosol Particles

Effects of Relative Humidity and Phase on the Molecular Detection of Nascent Sea Spray Aerosol Using Extractive Electrospray Ionization

Online mass spectrometry techniques, such as extractive electrospray ionization mass spectrometry (EESI-MS), present an attractive alternative for analyzing aerosol molecular composition due to reduced aerosol sample collection and handling times and improved time resolution. Recent studies show a dependence of EESI-MS sensitivity on particle size and mixing state. This study measured authentic sea spray aerosol (SSA) components generated during a phytoplankton bloom, specifically glycerol, palmitic acid, and potassium ions. We demonstrate temporal variability and trends dependent on specific biological processes occurring in seawater. We found that the EESI-MS sensitivity, after adjusting for pressure variations at the inlet and normalizing to the reagent ion, critically depends on the sample's relative humidity. Relevant SSA species exhibited heightened sensitivity at an elevated relative humidity near the deliquescence relative humidity of sea salt and poorer sensitivity with sparse detection below the efflorescence relative humidity. Modeling the reagent ion's diffusive depth demonstrates that the sample aerosol particle viscosity governs the relative humidity dependence because it modulates the particle's coagulation efficiency and distance the reagent ion diffuses and reacts with components in the particle bulk. The effects of particle size and mixing state are discussed, revealing improved sensitivity of phase-separated components present along the particle surface. This work highlights the importance of the particle phase state in detecting and quantifying molecular components within authentic and complex aerosol particles and the utility of EESI-MS for measuring SSA composition.

Direct Analysis of Soil Composition for Source Apportionment by Laser Ablation Single-Particle Aerosol Mass Spectrometry

Soil has always been the most complex biomaterial on the planet. The rapid determination of the components in the soil and their original source is a prerequisite for soil quality, environmental, and human health risk assessments. In this study, the chemical compositions and source apportionment of surface soil samples collected from five sites in Shanghai, China, were successfully investigated using a laboratory-developed laser ablation single-particle aerosol mass spectrometry (LA-SPAMS) instrument combined with an adaptive resonance theory-based neural network algorithm (ART-2a) data-processing method for the first time. In total, more than 35,000 particles, ranging from 200 to 2000 nm, were sized, and around 15-20% of the particles were chemically analyzed by LA-SPAMS to generate both positive and negative mass spectra. The results show that there are significant differences in particle size distribution among the five samples, with peaks of various sizes and different profiles, while all five soil samples contain crustal elements, heavy metals, organic and inorganic components, and so forth. The chemical composition of each sample varied considerably, so different classes of SPAMS particle classes were identified, which were later grouped into seven general categories: EC-rich (containing elemental carbon), secondary components, organic nitrogen, crust, HM (containing heavy metal), PAH (containing polycyclic aromatic hydrocarbons), and NaK-rich particles, based on the dominant marked ions. The composition analysis and source apportionment showed that soil components in different areas have been affected by the local environment, such as local industrial emissions and automobile exhaust, which are usually characterized by varying degrees of mixing between the crust and environmental aerosols. In combination with the ART-2a method, LA-SPAMS enables rapid and direct analysis of soil samples based on real-time single-particle measurements, which will help in understanding the distribution, transport, and fate of the soil components, thus providing new insights into soil-quality assessment. Moreover, the established LA-SPAMS can also be practically applied to other daily inspection tasks, such as rocks, minerals, metals, ceramics, polymers, and other solid materials for ingredient analysis and quality evaluation.

Individual particle investigation on the chloride depletion of inland transported sea spray aerosols during East Asian summer monsoon

Inland transported sea spray aerosol (SSA) particles along with multiphase reactions are essential to drive the regional circulation of nitrogen, sulfur and halogen species in the atmosphere. Specially, the physicochemical properties of SSA will be significantly affected by the displacement reaction of chloride. However, the role of organic species and the mixing state on the chloride depletion of SSA during long-range inland transport remains unclear. Hence, a single particle aerosol mass spectrometer (SPAMS) was employed to investigate the particle size and chemical composition of individual SSA particles over inland southern China during the East Asian summer monsoon. Based on the variation of chemical composition, SSA particles were clustered into SSA-Aged, SSA-Bio and SSA-Ca. SSA-Aged was regarded as the aged Na-rich SSA particles. In comparison to the SSA-Aged, SSA-Bio involved some extra organic species associated with biological origin (i.e., organic nitrogen and phosphate). Each type occupies for approximately 50% of total detected SSA particles. Besides, SSA-Ca may relate to organic shell of Na-rich SSA particles, which is negligible (~3%). Tight correlation between Na and diverse organic acids was exhibited for the SSA-Aged (r² = 0.52, p < 0.01) and SSA-Bio (r² = 0.61, p < 0.01), reflecting the impact of organic acids to the chloride displacement during inland transport SSA particles. The chloride depletion occupied by organic acids is estimated to be up to 34%. It is noted that distinctly different degree of chloride depletion was observed between SSA-Aged and SSA-Bio. It is more likely to be attributed to the associated organic coatings for the SSA-Bio particles, which inhibits the displacement reactions between acids and chloride. As revealed from the mixing state of SSA-Bio, defined hourly mean peak area ratio of Cl / Na increases with the increasing phosphate and organic nitrogen. This finding provides additional basis for the improvement of modeling simulations in chlorine circulation and a comprehensive understanding of the effects of organics on chloride depletion of SSA particles.

Evidence for brown carbon absorption over the Bay of Bengal during the southwest monsoon season: a possible oceanic source

The near UV-visible light-absorbing organic carbon (OC) of ambient aerosols, referred to here as brown carbon (BrC), significantly influences the atmospheric radiative forcing on both regional and global scales. Here, we documented BrC absorption in the aqueous and methanol extracts of marine aerosols collected over the Bay of Bengal (BoB: September-October 2017) and a city, Visakhapatnam (May-June 2018), in southern India during the southwest monsoon (i.e., a transition period with weak continental impact). The absorption spectra of BrC over the BoB showed several peaks around 300-400 nm and differ from those observed over Visakhapatnam. The absorption coefficient of BrC over the BoB, unlike Visakhapatnam data, does not seem to covary with other chemical proxies of biomass burning (non-sea-salt or nss-K+) and coal combustion (nss-SO42-) in the continental outflows, suggesting a different source of BrC over the BoB. Besides, we observed higher proportions of water-insoluble organic carbon (WIOC/OC: 0.89 ± 0.02) and significant enrichment of Mg2+ over Na+ (i.e., relative to seawater) in BoB aerosols. This result and the backward air mass trajectories both hinted their major source of OC from marine-derived organic matter. In contrast, the absorption spectra of BrC over Visakhapatnam are like those from biomass burning emissions in the Indo-Gangetic Plain. This observation is further supported by the satellite-based fire counts and backward air mass trajectories. Therefore, our study underscores the BrC aerosols from the oceanic sources and southern India, hitherto unknown, and can improve our understanding of the regional climate effects of carbonaceous aerosols if included in models.

Characteristics of single atmospheric particles in a heavily polluted urban area of China: size distributions and mixing states

To investigate the chemical composition, size distribution, and mixing state of aerosol particles on heavy pollution days, single-particle aerosol mass spectrometry was conducted during 9-26 October 2015 in Xi'an, China. The measured particles were classified into six major categories: biomass burning (BB) particles, K-secondary particles, elemental carbon (EC)-related particles, metal-containing particles, dust, and organic carbon (OC) particles. BB and EC-related particles were the dominant types during the study period and mainly originated from biomass burning, vehicle emissions, and coal combustion. According to the ambient air quality index, two typical episodes were defined: clean days (CDs) and polluted days (PDs). Accumulation of BB particles and EC-related particles was the main reason for the pollution in Xi'an. Most types of particle size were larger on PDs than CDs. Each particle type was mixed with secondary species to different degrees on CDs and PDs, indicating that atmospheric aging occurred. The mixing state results demonstrated that the primary tracers were oxidized or vanished and that the amount of secondary species was increased on PDs. This study provides valuable information and a dataset to help control air pollution in the urban areas of Xi'an. Graphical abstract.

Sea Spray Aerosol: Where Marine Biology Meets Atmospheric Chemistry

Atmospheric aerosols have long been known to alter climate by scattering incoming solar radiation and acting as seeds for cloud formation. These processes have vast implications for controlling the chemistry of our environment and the Earth's climate. Sea spray aerosol (SSA) is emitted over nearly three-quarters of our planet, yet precisely how SSA impacts Earth's radiation budget remains highly uncertain. Over the past several decades, studies have shown that SSA particles are far more complex than just sea salt. Ocean biological and physical processes produce individual SSA particles containing a diverse array of biological species including proteins, enzymes, bacteria, and viruses and a diverse array of organic compounds including fatty acids and sugars. Thus, a new frontier of research is emerging at the nexus of chemistry, biology, and atmospheric science. In this Outlook article, we discuss how current and future aerosol chemistry research demands a tight coupling between experimental (observational and laboratory studies) and computational (simulation-based) methods. This integration of approaches will enable the systematic interrogation of the complexity within individual SSA particles at a level that will enable prediction of the physicochemical properties of real-world SSA, ultimately illuminating the detailed mechanisms of how the constituents within individual SSA impact climate.