Chemistry of new particle growth during springtime in the Seoul metropolitan area, Korea

The investigations on organic sources and inorganic formation processes and their implications on haze during late winter in Seoul, Korea

This study investigated the sources and formation processes of particulate matter (PM) with an aerodynamic diameter ≤1 μm (PM₁) and black carbon (BC) in Seoul during late winter via high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS) and positive matrix factorization (PMF) analysis. In this study, secondary aerosols (75.1%) exhibited higher contributions than did primary aerosols (24.9%), suggesting the importance of secondary aerosol formation over primary aerosol emissions for NR-PM₁+BC during late winter. Frequent haze episodes were observed and these were found to proceed in two distinct stages each with different pattern of sulfur oxidation ratio (SOR), nitrogen oxidation ratio (NOR) and meteorological conditions, such as the wind speed, direction and relative humidity (RH). Haze formation during stage 1 was caused mainly by local accumulation of primary aerosols and formation of local secondary aerosols under stagnant conditions. However, there were some impacts of down mixing of regional transport. Stage 2 took place during the night following stage 1 and was characterized by enhanced secondary aerosol formation. Enhancement of SOR might be due to accelerated aqueous phase reactions under higher RH and enhanced NOR is probably because of the heterogeneous uptake of N₂O₅ by ammonium sulfate aerosols ensued after sulfate formation. These findings suggest that the winter air quality in Seoul depends on complex processes, from not only emissions and transport from upwind areas but also from significant impacts of meteorological condition.

The impact of size-segregated particle properties on daily mortality in Seoul, Korea

To investigate the causative component for certain health outcomes, the associations between the properties of ambient particles and cause-specific mortality (all-cause, cardiovascular, and respiratory-related mortality) measured in Seoul, Korea, from January 1, 2013, to December 31, 2016, were evaluated with a quasi-Poisson generalized additive model (GAM). The total mass of PM₁₀ and PM_2.5 moderately affected respiratory-related mortality but had almost no impact on all-cause and cardiovascular-related mortality. Among PM_2.5 mass compositions, ammonium sulfate, which is in generally 300-500 nm as a secondary species, showed the most statistically significant effect on respiratory-related mortality at lag 4 (p < 0.1) but not for other mortalities. However, from the size-selective investigations, cardiovascular-related mortality was impacted by particle number concentrations (PNCs), particle surface concentrations (PSCs), and particle volume concentrations (PVCs) in the size range from 50 to 200 nm with a statistically significant association, particularly at lag 1, suggesting that mass is not the only way to examine mortality, which is likely because mass and chemical composition concentrations are generally controlled by larger-sized particles. Our study suggests that the size-specific mortality and/or impacts of size-resolved properties on mortalities need to be evaluated since smaller particles get into the body more efficiently, and therefore, more diverse size-dependent causes and effects can occur.

Chemical characterization and sources of submicron aerosols in Lhasa on the Qinghai-Tibet Plateau: Insights from high-resolution mass spectrometry

In recent years, a great number of studies has been carried out in urban cities regarding urban particulate matter (PM) pollution in China, especially in eastern China. Lhasa, the capital of the Tibet Autonomous Region in western China, is the highest (3650 m a.s.l.) city in China and has notably different lifestyles and PM sources comparing with those in eastern China. However, there is currently a lack of studies on PM pollution in this city. In this study, an Aerodyne high-resolution time-of-flight aerosol mass spectrometer was deployed along with other co-located instruments to explore the chemical characterization of ambient submicron PM (PM₁) in Lhasa from 31 August 2019 to 26 September 2019. The mean ambient PM₁ mass loading through this study was 4.72 μg m^-3. Organic aerosols (OAs) played a dominant role with an average contribution of 82.6% to PM₁, followed by 5.4% nitrate, 4.7% ammonium, 3.4% sulfate, 3.1% BC, and 0.7% chloride. The relatively lower contribution from secondary inorganic aerosols (nitrate and sulfate) in this study was distinctly different from that in eastern China, indicating lower fossil fuel usage in this city. Via positive matrix factorization (PMF), organic aerosols were decomposed into four components containing a traffic-related hydrocarbon-like OA (HOA), a cooking-related OA (COA), a biomass burning-related OA (BBOA), as well as an oxygenated OA (OOA). The OOA and COA had higher contributions (34% and 35%, respectively) to total OAs, while the rest accounted for 17% for HOA and 14% for BBOA. However, an increased mass fraction of BBOA (up to 36%) was found during the Sho Dun Festival, suggesting the importance of biomass burning emissions during the religious activities in this city. Frequent new particle formation events were observed during this study and the contribution of chemical species for the particle growth was also explored.

CHEMICAL REACTION MONITORING BY AMBIENT MASS SPECTROMETRY

Chemical reactions conducted in different media (liquid phase, gas phase, or surface) drive developments of versatile techniques for the detection of intermediates and prediction of reasonable reaction pathways. Without sample pretreatment, ambient mass spectrometry (AMS) has been applied to obtain structural information of reactive molecules that differ in polarity and molecular weight. Commercial ion sources (e.g., electrospray ionization, atmospheric pressure chemical ionization, and direct analysis in real-time) have been reported to monitor substrates and products by offline reaction examination. While the interception or characterization of reactive intermediates with short lifetime are still limited by the offline modes. Notably, online ionization technologies, with high tolerance to salt, buffer, and pH, can achieve direct sampling and ionization of on-going reactions conducted in different media (e.g., liquid phase, gas phase, or surface). Therefore, short-lived intermediates could be captured at unprecedented timescales, and the reaction dynamics could be studied for mechanism examinations without sample pretreatments. In this review, via various AMS methods, chemical reaction monitoring and mechanism elucidation for different classifications of reactions have been reviewed. The developments and advances of common ionization methods for offline reaction monitoring will also be highlighted.

Sources, species and secondary formation of atmospheric aerosols and gaseous precursors in the suburb of Kitakyushu, Japan

The simultaneous assessment of source apportionment and secondary formation processes was comprehensively studied in a suburban area located on the western edge of Japan by combining year-round daily observation using a filter-pack method with model calculations. Secondary formation was the most important pollution source, accounting for ca. 45% (23% (secondary sulfates) + 22% (secondary nitrates)) of the sources of total atmospheric aerosol mass. For the secondary aerosol composition at this suburban site in western Japan, the secondary sulfates were mainly derived from volcanic eruptions (Sakurajima volcano and/or Aso volcano), the oxidation of SO₂ from industrial combustion, ship emissions in the Kyushu area, and long-distance transportation from several coastal cities in Eastern China. Multiple regression results further revealed that the secondary sulfate formation process was significantly influenced by and related to HNO₃, HCl, and the relative humidity (RH) (p < 0.01). While the potential pollution source region of secondary nitrates was located in the northwest region of the sampling site, where air masses pass through Mongolia and Northern China, the formation mechanism of secondary nitrates was more complicated, with the important driving factors being Ox, NO₂, NH₃, HCl, temperature (T), and RH. In addition, if the presence of atmospheric HNO₃ was ignored, the nitrogen oxidation rate (NOR) would be significantly underestimated, especially at relative humidity levels less than 60% and temperatures greater than 16 °C. The results of this study clearly demonstrate the source contribution and characteristics of secondary aerosols in the suburban area of western Japan and can be adopted as the important basis to mitigate particle pollution.

Pollution sources of atmospheric fine particles and secondary aerosol characteristics in Beijing

To investigate the secondary formation and pollution sources of atmospheric particles in urban Beijing, PM_2.5 and its chemical components were collected and determined by URG-9000D ambient ion monitor (AIM) from March 2016 to January 2017. Among water-soluble ions (WSIs), NO₃^-, SO₄^2- and NH₄⁺ (SNA) had the largest proportion (77.8%) with the total concentration of 23.8 μg/m³. Moreover, as fine particle pollution worsened, the NO₃^-, SO₄^2- and NH₄⁺ concentrations increased basically, which revealed that secondary aerosols were the main cause of particle pollution in Beijing. Furthermore, the particle neutralization ratio (1.1), the ammonia to sulfate molar ratio (3.4) and the nitrate to sulfate molar ratio (2.2) showed that secondary aerosols are under ammonium-rich conditions with the main chemical forms of NH₄NO₃ and (NH₄)₂SO₄, and vehicle emission could be the main anthropogenic source of secondary aerosols in Beijing. Source analysis further indicated that secondary aerosols, solid fuel combustion, dust and marine aerosol were the principal pollution sources of PM_2.5, accounting for about 46.1%, 22.4% and 13.0%, respectively, and Inner Mongolia and Hebei Provinces could be considered as the main potential sources of PM_2.5 in urban Beijing. In addition, secondary formation process was closely related with gaseous precursor emission amounts (SO₂, NO₂, NH₃ and HONO), atmospheric ozone concentration (O₃), meteorological conditions (temperature and relative humidity) and particle components. Sensitive analysis of the thermodynamic equilibrium model (ISORROPIA II) revealed that controlling total nitrate (TN) is the effective measure to mitigate fine particle pollution in Beijing.