Revealing the Contribution of Interfacial Processes to Atmospheric Oxidizing Capacity in Haze Chemistry.

The atmospheric oxidizing capacity is the most important driving force for the chemical transformation of pollutants in the atmosphere. Traditionally, the atmospheric oxidizing capacity mainly depends on the concentration of O3 and other gaseous oxidants. However, the atmospheric oxidizing capacity based on gas-phase oxidation cannot accurately describe the explosive growth of secondary particulate matter under complex air pollution. From the chemical perspective, the atmospheric oxidizing capacity mainly comes from the activation of O2, which can be achieved in both gas-phase and interfacial processes. In the heterogeneous or multiphase formation pathways of secondary particulate matter, the enhancement of oxidizing capacity ascribed to the O2/H2O-involved interfacial oxidation and hydrolysis processes is an unrecognized source of atmospheric oxidizing capacity. Revealing the enhanced oxidizing capacity due to interfacial processes in high-concentration particulate matter environments and its contribution to the formation of secondary pollution are critical in understanding haze chemistry. The accurate evaluation of atmospheric oxidizing capacity ascribed to interfacial processes is also an important scientific basis for the implementation of PM2.5 and O3 collaborative control in China and around the world.

Marine Submicron Aerosols from the Gulf of Mexico: Polluted and Acidic with Rapid Production of Sulfate and Organosulfates.

We measured submicron aerosols (PM1) at a beachfront site in Texas in Spring 2021 to characterize the "background" aerosol chemical composition advecting into Texas and the factors controlling this composition. Observations show that marine "background" aerosols from the Gulf of Mexico were highly processed and acidic; sulfate was the most abundant component (on average 57% of total PM1 mass), followed by organic material (26%). These chemical characteristics are similar to those observed at other marine locations globally. However, Gulf "background" aerosols were much more polluted; the average non-refractory (NR-) PM1 mass concentration was 3-70 times higher than that observed in other clean marine atmospheres. Anthropogenic shipping emissions over the Gulf of Mexico explain 78.3% of the total measured "background" sulfate in the Gulf air. We frequently observed haze pollution in the air mass from the Gulf, with significantly elevated concentrations of sulfate, organosulfates, and secondary organic aerosol associated with sulfuric acid. Analysis suggests that aqueous oxidation of shipping emissions over the Gulf of Mexico by peroxides in the particles might potentially be an important pathway for the rapid production of acidic sulfate and organosulfates during the haze episodes under acidic conditions.

Role of secondary aerosols in haze formation in summer in the Megacity Beijing.

A field experiment from 18 August to 8 September 2006 in Beijing, China, was carried out. A hazy day was defined as visibility

Interactions between Starmerella bacillaris and Saccharomyces cerevisiae during sequential fermentations influence the release of yeast mannoproteins and impact the protein stability of an unstable wine.

Wine protein haze formation is a problem due to grape proteins aggregation during wine storage. The cell wall components of wine yeasts, particularly high molecular weight mannoproteins, have a protective effect against haze formation, although their involvement remains poorly understood. This study aimed at characterizing glycosylated proteins released by Starmerella bacillaris and Saccharomyces cerevisiae during single and sequential fermentations in a synthetic must, and testing their impact on wine protein stability. Mannoproteins-rich extracts from sequential fermentations showed an increase in the low MW polysaccharide fraction and, when added to an unstable wine, had a greater effect on protein stability than S. cerevisiae extracts. Shotgun proteomics approaches revealed that the identified cell wall proteins exclusively found in sequential fermentations were produced by both S. bacillaris (MKC7, ENG1) and S. cerevisiae (Bgl2p). Moreover, sequential fermentations significantly increased the expression of Scw4p and 1,3-beta-glucanosyltransferase (GAS5), produced by S. cerevisiae. Finally, some of the key proteins identified might play a positive role in increasing wine protein stability.

Explosive morning growth phenomena of NH3 on the North China Plain: Causes and potential impacts on aerosol formation.

Atmospheric ammonia (NH3) as the most important alkaline gas in the atmosphere has attracted much attention in recent years due to its critical role in haze formation, especially on the North China Plain (NCP). Comprehensive studies are needed for investigating diurnal variations of NH3 and underlying mechanisms in different seasons and their potential impacts on atmospheric chemistry. In this study, continuous long-term observation (Mar. 2016 to May 2017) of NH3 at a rural site in the NCP was used to characterize the diurnal variation of NH3 in different seasons and to unveil its causes and potential impacts on atmospheric chemistry. NH3 concentrations displayed rapid increases during the morning, reaching very prominent peaks mostly between 8:00 to 11:00 LT. Such frequent (55%) morning peaks were mainly caused by the evaporation of dew and guttation water droplets. Average dew and guttation water volume concentrations of 750 mL m-2 was estimated for spring, which resulted in approximate NH3 emissions of 800 ng m-2 s- 1. Such high emission fluxes from dew and guttation water evaporation have never been reported before, suggesting dew and guttation droplets to be significant night-time reservoirs and strong morning sources for NH3. In light of recent studies putting forward that NH3 can promote the heterogeneous formation of HONO and nitrate under high humidity conditions, we investigated the differences in HONO and aerosol chemical composition diurnal variations between days with and without NH3 morning spikes during November. HONO, nitrate and sulfate concentrations were significantly higher for days with NH3 morning spikes, with HONO displaying a morning peak near that of NH3. These results demonstrate that the prevailing NH3 morning spikes on the NCP have significant influences on aerosol formation and atmospheric chemistry. NH3 emission mitigation strategies and regulations are urgently needed.

Airborne microorganisms exacerbate the formation of atmospheric ammonium and sulfate.

Haze pollution is inseparable from the transformation of air pollutants especially the ammonium and sulfate. Chemical and physical processes play important roles in this transformation. However, the role of microbial processes has rarely been studied. In this report, we applied the cultivation-independent metagenomic approach to study airborne microorganisms, investigating the potential microbial-catalyzed transformation of ammonium and sulfate in PM2.5 samples. Functional genes predict that airborne microorganisms have the potential to catalyze ammonium formation but not ammonium oxidation since no ammoxidation genes were identified. We also found that the frequency of sulfate-forming genes was 1.56 times of those for sulfate-reducing genes. It was speculated that microbial metabolisms in the atmosphere could contribute to the accumulation of ammonium and sulfate. With the increase of PM2.5 concentration, the frequency of functional genes and the relative abundance of genera which involved in nitrogen and sulfur metabolisms increased. That suggested air pollution was conducive to the microbial-mediated formation of ammonium and sulfate. Overall, our results provided evidence for the possible role of microbial processes in the air pollutant transformation and brought a new perspective for studying the formation of secondary air pollutants.

Wine Thermosensitive Proteins Adsorb First and Better on Bentonite during Fining: Practical Implications and Proposition of Alternative Heat Tests.

Bentonite fining is the most popular treatment used to remove proteins in white and rosé wines. The usual heat test used to adjust the bentonite dose consists of heating the wine during 30 min at 80 °C. At this temperature, all of the proteins are unfolded, and this can lead to an overestimation of the dose. We have shown that proteins adsorb on bentonite in a specific order and, more importantly, that the proteins responsible for haze formation adsorb first. Fluorescence spectroscopy showed that this is due to the structural properties of proteins, which can be classified as hard and soft proteins. Alternative heat tests were performed at a lower temperature (40 °C) and showed a better correlation with accelerated aging. These tests were also less dependent upon the wine pH.

Characteristics and secondary formation of water-soluble organic acids in PM1, PM2.5 and PM10 in Beijing during haze episodes.

Water-soluble organic acids are widely involved in various atmospheric physicochemical processes and appear as an important fraction of atmospheric aerosols. Nineteen water-soluble organic acids in 12-h PM1, PM2.5 and PM10 samples collected in urban Beijing during haze episodes in winter and spring of 2017 were identified to investigate their characteristics and secondary formation mechanism. The molecular distributions of water-soluble organic acids as well as the high ratio of phthalic acid (Ph)/azelaic acid (C9) indicated severe aromatic secondary organic aerosol pollution during the haze episodes, especially in winter. The diurnal patterns, size distributions, and concentration ratios of specific organic acids were investigated to reveal the pollution characteristics and possible sources of major organic acids in particulate matter in Beijing during haze events. Multiple linear regression was used to tentatively quantify the relative contributions of photochemical oxidation and aqueous-phase oxidation to the formation of total water-soluble organic acids in PM1, PM2.5 and PM10 during haze episodes. The formation mechanism of sulfate and nitrate was also investigated for comparison. Different from the secondary formation of sulfate, the secondary formation of water-soluble organic acids showed enhanced contribution of gas-phase photochemical oxidation though the aqueous-phase oxidation was the dominant process. CAPSULE: Molecular analyses of organic acids in PM1, PM2.5 and PM10 in Beijing during haze periods revealed their pollution characteristics, possible sources and formation mechanism.

Increasing importance of nitrate formation for heavy aerosol pollution in two megacities in Sichuan Basin, southwest China.

Secondary inorganic aerosols, including sulfate, nitrate, and ammonium contribute to a large extent to the severe haze pollution events in China. Understanding their formation mechanisms is critical for designing effective mitigation strategies to control haze pollution, especially as the role of nitrate seemed to become more important recently, especially in some megacities. In the present study, simultaneous observations were conducted in two megacities (Chengdu and Chongqing) in Sichuan Basin of southwest China, one of the regions suffering from severe aerosol pollution. One typical long-lasting pollution event in Chengdu and Chongqing was captured during wintertime from December 25, 2016 to January 5, 2017. The campaign-average of hourly concentrations of PM2.5, sulfate, and nitrate, measured by an Aerosol Analyzer (ZSF) were 101 ±â€¯73.8 µg/m3, 15.9 ±â€¯11.8 µg/m3, and 24.9 ±â€¯20.6 µg/m3, respectively, in Chengdu, and were 87.7 ±â€¯53.8 µg/m3, 19.7 ±â€¯13.5 µg/m3, and 15.1 ±â€¯10.1 µg/m3, respectively, in Chongqing. Nitrate contributed substantially to PM2.5 pollution when PM2.5 was lower than 150 µg/m3, largely due to the strong secondary transformation of NOX to nitrate during the occurrence of the pollution episode. Heterogeneous hydrolysis of N2O5 dominated nitrate formation during nighttime, while photochemical reactions and high-RH enhanced gas- to aqueous-phase dissolution of NH3 and HNO3 or cloud processes likely played important roles for nitrate formation during daytime. RH-dependent heterogeneous reactions contributed greatly to the formation of sulfate. NOX is confirmed to play an important role as an oxidant in accelerating the secondary transformation of SO2 to sulfate at high RH and low O3 levels under neutralization condition during heavy PM2.5 pollution episode. Results from this study identified the formation mechanism of nitrate, especially during the daytime, and addressed the importance of heterogeneous inorganic reactions in the formation of heavy aerosol pollution events.

Quantitative evaluation of haze formation of koji and progression of internal haze by drying of koji during koji making.

The construction of an experimental system that can mimic koji making in the manufacturing setting of a sake brewery is initially required for the quantitative evaluation of mycelia grown on/in koji pellets (haze formation). Koji making with rice was investigated with a solid-state fermentation (SSF) system using a non-airflow box (NAB), which produced uniform conditions in the culture substrate with high reproducibility and allowed for the control of favorable conditions in the substrate during culture. The SSF system using NAB accurately reproduced koji making in a manufacturing setting. To evaluate haze formation during koji making, surfaces and cross sections of koji pellets obtained from koji making tests were observed using a digital microscope. Image analysis was used to distinguish between haze and non-haze sections of koji pellets, enabling the evaluation of haze formation in a batch by measuring the haze rate of a specific number of koji pellets. This method allowed us to obtain continuous and quantitative data on the time course of haze formation. Moreover, drying koji during the late stage of koji making was revealed to cause further penetration of mycelia into koji pellets (internal haze). The koji making test with the SSF system using NAB and quantitative evaluation of haze formation in a batch by image analysis is a useful method for understanding the relations between haze formation and koji making conditions.

PM2.5 pollution is substantially affected by ammonia emissions in China.

Urban air quality in China has been declining substantially in recent years due to severe haze episodes. The reduction of sulfur dioxide (SO2) and nitrogen oxide (NOx) emissions since 2013 does not yet appear to yield substantial benefits for haze mitigation. As the reductions of those key precursors to secondary aerosol formation appears not to sufficient, other crucial factors need to be considered for the design of effective air pollution control strategies. Here we argue that ammonia (NH3) plays a - so far - underestimated role in the formation of secondary inorganic aerosols, a main component of urban fine particulate matter (PM2.5) concentrations in China. By analyzing in situ concentration data observed in major cities alongside gridded emission data obtained from remote sensing and inventories, we find that emissions of NH3 have a more robust association with the spatiotemporal variation of PM2.5 levels than emissions of SO2 and NOx. As a consequence, we argue that urban PM2.5 pollution in China in many locations is substantially affected by NH3 emissions. We highlight that more efforts should be directed to the reduction of NH3 emissions that help mitigate PM2.5 pollution more efficiently than other PM2.5 precursors. Such efforts will yield substantial co-benefits by improving nitrogen use efficiency in farming systems. As a consequence, such integrated strategies would not only improve urban air quality, but also contribute to China's food-security goals, prevent further biodiversity loss, reduce greenhouse gas emissions and lead to economic savings.

Influence of polysaccharides on wine protein aggregation.

Polysaccharides are the major high-molecular weight components of wines. In contrast, proteins occur only in small amounts in wine, but contribute to haze formation. The detailed mechanism of aggregation of these proteins, especially in combination with other wine components, remains unclear. This study demonstrates the different aggregation behavior between a buffer and a model wine system by dynamic light scattering. Arabinogalactan-protein, for example, shows an increased aggregation in the model wine system, while in the buffer system a reducing effect is observed. Thus, we could show the importance to examine the behavior of wine additives under conditions close to reality, instead of simpler buffer systems. Additional experiments on melting points of wine proteins reveal that only some isoforms of thaumatin-like proteins and chitinases are involved in haze formation. We can confirm interactions between polysaccharides and proteins, but none of these polysaccharides is able to prevent haze in wine.

Effects of high hydrostatic pressure (HHP) on the protein structure and thermal stability of Sauvignon blanc wine.

Protein haze development in bottled white wines is attributed to the slow denaturation of unstable proteins, which results in their aggregation and flocculation. These protein fractions can be removed by using bentonite; however, a disadvantage of this technique is its cost. The effects of high hydrostatic pressure (HHP) on wine stability were studied. Fourier transform infrared spectroscopy experiments were performed to analyse the secondary structure of protein, thermal stability was evaluated with differential scanning calorimetry, while a heat test was performed to determine wine protein thermal stability. The results confirmed that high pressure treatments modified the α-helical and ß-sheet structures of wine proteins. Throughout the 60 days storage period the α-helix structure in HHP samples decreased. Structural changes by HHP (450 MPa for 3 and 5 min) improve thermal stability of wine proteins and thus delay haze formation in wine during storage.