Formation Mechanism Of PM2 Research Articles

Chemical characteristics, sources, and formation mechanisms of PM2.5 before, during, and after the Spring Festival in a plateau city of Southwest China

To study chemical characteristics, sources and formation mechanisms of PM2.5 during the Spring Festival (SF), 39 elements, 9 water–soluble ions (WSIs) and 8 fractions of carbonaceous species in PM2.5 and PM10 at two sites in Kunming were investigated. The results indicated that the average mass concentration of PM2.5 and PM10 were 61.03 ± 25.11 and 80.48 ± 30.08 μg/m3 in the urban area, and 18.96 ± 4.66 and 56.76 ± 21.69 μg/m3 in the suburban area, respectively. Concentrations of PM2.5 peaked significantly on the Chinese New Year (NYE) and the Lantern Festival (LF) in the urban area. Compared to the previous day of NYE, Ba and Sr concentrations increased by 22.1 and 39.2 times in urban areas, and by 6.5 and 8.3 times in suburban areas. The sum of sulfate, nitrate, and ammonium (SNA) accounted for 82.03% and 60.38% of WSIs in urban and suburban areas, respectively. The most abundant carbonaceous species in urban and suburban areas were OC3 and EC1. According to the Positive Matrix Factorization (PMF) calculation, secondary formation (41.76%) was the predominant sources of PM2.5, and the contribution of fireworks to PM2.5 was 9.06%. The formation of secondary organic carbon (SOC) occurred through heterogeneous reactions. SNA was derived from heterogeneous reaction and photochemical reaction.

Chemical characteristics and formation mechanisms of PM2.5 during wintertime in two cities with different industrial structures in the Sichuan Basin, China

PM2.5 remains one of the critical pollutants involving regional and complex air pollution in many big cities of China, and its improvement has become sluggish in recent years. In this study, we collected PM2.5 samples from two cities, Chengdu and Ya'an, which have different industrial structures in the Sichuan basin during wintertime and investigated the reasons behind their severe PM2.5 pollution. Throughout the entire sampling period, the average PM2.5 concentrations in Chengdu (71.3 ± 24.8 μg/m3) and Ya'an (72.6 ± 27.1 μg/m3) were similar. However, the chemical compositions of PM2.5 showed significant differences. Chengdu exhibited higher concentrations of water-soluble inorganic ions, whereas Ya'an had higher levels of carbonaceous compounds. Both cities experienced an ammonium-rich environment, which promoted the homogeneous generation of secondary pollutants. Moreover, as PM2.5 pollution worsened, the influence of heterogeneous reactions involving SO2 and NOx, as well as the heterogeneous hydrolysis of N2O5, gradually became more pronounced in particle formation. Additionally, adverse meteorological conditions facilitated pollutant accumulation in Ya'an. Using the Positive Matrix Factorization model, we identified 5 sources of PM2.5. The primary source of PM2.5 in both cities was secondary formation (35.4% in Chengdu and 32.5% in Ya'an), while their second-largest contributors varied (26.2% from vehicle emission in Chengdu, and 26.6% from combustion source in Ya'an). These discrepancies highlight the necessity for tailored government interventions, particularly during the winter season. By analyzing the light absorption of the carbonaceous at 370 nm, we discovered that brown carbon was the primary absorber of near-ultraviolet light, with vehicle emissions accounting for the largest portion in Chengdu (37.2%) and combustion emissions being the predominant factor in Ya'an (51.0%). These results could potentially help for having a long-term impact on climate change by simultaneously reducing PM2.5 pollution.

Differences in the chemical compositions and formation mechanisms of PM2.5 between urban and rural areas in Xinxiang, Central China around the Beijing Winter Olympics

Xinxiang, as an important industrial city in Henan Province and one of the “2 + 26” cities, is encountering severe fine particulate matter (PM2.5) pollution. During the Beijing Winter Olympics Games, a series of pollution control measures were implemented in Xinxiang, which provides an excellent opportunity to investigate the local PM2.5 characteristics and formation mechanisms and assess the effectiveness of the control measures. From January 20 to February 20, 2022, samples of PM2.5 were collected in urban and rural areas of Xinxiang, and their chemical compositions were detected. Three research phases were divided according to control measures: P1, P2 and P3, representing before pollution control period, stricter pollution control period, and looser pollution control period, respectively. It was found that PM2.5 levels decreased significantly during P2 and P3, by more than 30%. There was a significant decrease in SO42−, NO3− and NH4+ (SNA) in PM2.5, but not in organic carbon (OC) and element carbon. Moreover, the secondary formations of SO42− and NO3− also decreased clearly during these two phases, especially for nocturnal NO3−. SO42− was mainly generated through the NO2 reaction pathway (SO2 oxidation by NO2 in aerosol water), and the reaction could also promote NO3− production. As NO2 is critical in this reaction, future pollution control should focus on reducing NO2. The PM2.5 in urban and rural areas had quite different compositions. Specifically, the rural area had better reaction conditions for sulfate (lower temperature). In addition, urban area had more OC that came from secondary reactions, while in rural area it comes more from biomass and coal combustion. Therefore, different pollution control measures should be taken to reduce their OC concentrations in the future. The study will provide a more scientific basis for formulating more scientific control measures of PM2.5 in Xinxiang and other cities in Central China.

Emission characteristics and formation mechanisms of PM2.5 and gases from different geological maturities coals combustion

To evaluate the influence of geological maturity on coal combustion pollutant emissions, six chunk coals and corresponding briquettes (volatile matter [VM] content from 8.0% to 39.9%) were selected for simulated residential combustion in a carefully designed chamber, and the formation mechanism involved was investigated. VM was revealed to have a nonlinear effect on the emission factors (EFs) of particulate matter with an aerodynamic diameter of <2.5 μm (PM2.5), polycyclic aromatic hydrocarbons (PAHs), elemental carbon (EC), and organic carbon (OC), with the highest EFs observed in VM of 15.8% and 26.8%. Coal tar yield and air-supply from VM combustion in its initial stage was found to be a key factor influencing PM2.5 and PAH emissions when compared with the char combustion and burnout stages. The highest PM2.5 and PAH EFs were observed in coal with 15.8% VM. Additionally, significant amounts of hydrogen cyanide (HCN) were detected at stage 1 and were released as volatile-N through the pyrolysis of coal-N. N2O and NOx were also emitted through homogeneous gas-phase HCN reactions. However, only a small proportion of NOx was produced, indicating that the contribution of VM to HCN and N2O emissions is greater than that of NOx. In the char reaction stage (stage 2), char-N reacted with O2 to form large amounts of NO, and the reaction length of the entire coal combustion process exhibited a positive relationship with coal maturity (correlation coefficient 0.69, p < 0.05), suggesting that the contribution of NO from char-N to overall NO emissions increased with the coal’s geological maturity due to the increase in coal-N retention in char. Furthermore, coal briquetting was found to decrease the EFs of pollutants, which may be explained by an increase in MCE (modified combustion efficiency) and the conversion from coal tar to carbon and hydrogen. This study elucidated the effects of geological maturity on pollutant emissions from coal combustion and examined relevant underlying mechanism. These data can serve as the foundation for a clean coal project in China or other counties concerned with coal combustion emissions.

Emission characteristics and formation mechanisms of PM2.5 from co-firing of algal biomass and coal

To address the emissions and formation of fine particulate matter (PM2.5) from co-firing of algal biomass (Chlorella (Ch), Sargassum (Sa), and Enteromarpha (En)) and pulverized coal (Huating coal), the emission characteristics were experimentally investigated using a one-dimensional tubular furnace. The results indicate that algae species, the mixing ratio, and the reaction temperature have complex impacts on PM2.5 emissions. Its emission characteristics present either single- or double-peak distribution. The higher temperature and higher biomass fraction accelerate the formation of PM2.5 during co-firing. Different from the reduction in NOx and SO2 emissions, the PM2.5 emission from algal biomass-based co-firing is higher than that of coal alone on the whole, particularly for Sa and En. For En, the maximum PM2.5 concentration occurred at 900 °C with 91.73 mg/m3 when 20% En was co-fired with 80% coal. Meanwhile, the PM2.5 emission yield reached the peak of 553.64 ( × 10−2) mg/g. For Sa, the highest PM2.5 concentration and PM2.5 emission yield appeared when 20% Sa and 80% coal were co-fired at 1000 °C, were 125.30 mg/m3 and 354.41 ( × 10−2) mg/g, respectively. For Ch, the highest PM2.5 concentration appeared when 20% Ch and 80% coal were co-fired at 1000 °C and reached 1.11 mg/m3, but the largest PM2.5 emission yield was 3.21 ( × 10−2) mg/g when 20% Ch and 80% coal were co-fired at 1100 °C. PM2.5 generated from co-firing are mainly formed by vaporization and homogeneous/heterogeneous condensation, as well as fragmentation of internal/external minerals and char particles. In addition, it also depends upon a series of reactions between the alkali metal salt and other incombustible particles. The morphological characteristics of ash residues from Ch co-fired with coal were irregular and fragmented, and the structure was relatively compact, and those for Sa and En co-fired with coal are similar, both of which are irregular massive structures with white crystal particles attached.

Source apportionment of PM2.5 and sulfate formation during the COVID-19 lockdown in a coastal city of southeast China

Revealing the changes in chemical compositions and sources of PM2.5 is important for understanding aerosol chemistry and emission control strategies. High time-resolved characterization of water-soluble inorganic ions, elements, organic carbon (OC), and elemental carbon (EC) in PM2.5 was conducted in a coastal city of southeast China during the COVID-19 pandemic. The results showed that the average concentration of PM2.5 during the city lockdown (CLD) decreased from 46.2 μg m−3 to 24.4 μg m−3, lower than the same period in 2019 (PM2.5: 37.1 μg m−3). Concentrations of other air pollutants, such as SO2, NO2, PM10, OC, EC, and BC, were also decreased by 27.3%–67.8% during the CLD, whereas O3 increased by 28.1%. Although SO2 decreased from 4.94 μg m−3to 1.59 μg m−3 during the CLD, the concentration of SO42− (6.63 μg m−3) was comparable to that (5.47 μg m−3) during the non-lockdown period, which were attributed to the increase (16.0%) of sulfate oxidation rate (SOR). Ox (O3+NO2) was positively correlated with SO42−, suggesting the impacts of photochemical oxidation. A good correlation (R2 = 0.557) of SO42− and Fe and Mn was found, indicating the transition-metal ion catalyzed oxidation. Based on positive matrix factorization (PMF) analysis, the contribution of secondary formation to PM2.5 increased during the epidemic period, consisting with the increase of secondary organic carbon (SOC), while other primary sources including traffic, dust, and industry significantly decreased by 9%, 8.5%, and 8%, respectively. This study highlighted the comprehensive and nonlinear response of chemical compositions and formation mechanisms of PM2.5 to anthropogenic emissions control under relatively clean conditions.

Stoichiometric characteristics and economic implications of water-soluble ions in PM2.5 from a resource-dependent city

The stoichiometric characteristics of water-soluble ions (WSIs) in PM2.5, which can be used as an indicator socioeconomic development level, are mostly depending on the sources and formation mechanism of PM2.5. This work presents the stoichiometric characteristics and socioeconomic linkage of WSIs in PM2.5 from a resource-dependent city. The relationship between NO3−/SO42− and car parc indexes the contribution of mobile emission source. The equivalent ratio of WSIs suggested that aerosol particles were weak acidic due to the deficiency of cations in PM2.5, which was consistent with the average annual pH (6.27) of precipitation in Wuhai in 2015. NH4+ neutralizes PM2.5 acidity in clean and polluted days, while Ca2+ and NH4+ in dust storm days. Furthermore, the PCA analysis indicated the multi-sources pollution characteristics from Spring to Fall, which was related the small build-up area (only 62.30 km2) and the close-set of various industrial enterprises in Wuhai. The ratios of NO2/SO2 may not work effectively to identify the importance of mobile versus stationary pollution emission sources when the heavy emission from the secondary industry, especially the proportion of secondary industry higher than 65% and the ratios of NO2/SO2 lower than 0.4. This work contributes to more effective control strategies for PM2.5 in resource-dependent areas.

Acidity and inorganic ion formation in PM2.5 based on continuous online observations in a South China megacity

To investigate the evolutionary characteristics and formation mechanisms of PM2.5 in areas with high environmental capacity, Shenzhen, a representative megacity on the southeast coast of China, was chosen for analysis in this study. Continuous quantitative observations of the mass concentrations of PM2.5, water-soluble inorganic ions (WSIIs) in PM2.5 and relevant reactive gaseous precursors were conducted for 1 year at an urban site in Shenzhen. The differences in the meteorological factors and in the major air pollutants between the polluted and clean periods were compared in detail. Daily air quality index (AQI) values were used to distinguish these two periods. Using the ISORROPIA-II thermodynamic equilibrium model, aerosol pH and liquid water content measurements were obtained for the first time during both the polluted period and the clean period. The aerosol pH values during the polluted period and the clean period were determined to be 7.55 ± 0.58 and 4.23 ± 2.99, respectively. The secondary conversion efficiencies of SO2 and NO2 to sulfate and nitrate, respectively, were found to increase during the polluted period. The polluted period exhibited a combination of both high PM2.5 and high O3 pollution. In the clean period, the ozone concentrations remained at high levels despite a significant drop in PM2.5 levels. The potential sources and transportation modes of air pollution in Shenzhen were also discussed.

Concentration Characteristics of PM2.5 and the Causes of Heavy Air Pollution Events in Beijing During Autumn and Winter

To study the changing of characteristics and formation mechanisms of PM2.5 in Beijing during the last two years, particulate matter concentrations, weather conditions, and air-mass trajectories were analyzed during severe pollution episodes in fall and winter 2016-2017 using routine observations and the TrajStat model. Results showed that 13 heavy pollution events, each lasting at least two days, occurred in Beijing. Of these, approximately 61.5% occurred in winter, characterized by heavier pollution concentrations and longer durations than those occurring in autumn. A low-pressure gradient, high humidity, low surface wind speed, low boundary layer, and particular terrain (i. e., being surrounded by mountains on three sides) all contributed to the high occurrence frequency of severe pollution episodes in autumn and winter. During the pollution episodes, the average ratio of PM2.5 to PM10 reached 0.86. The air-masses during the accumulation stage were mainly transported from the northwest, west, southwest, and southeast of Beijing. The southwestern and southeastern transmission paths accounted for 21.6% of the total pollution load. In addition, the WRF-CAMx model was used to quantitatively analyze the contributions of local and external sources to the concentrations of PM2.5 in Beijing during 16-22 December 2016. Based on this analysis, PM2.5 contributions notably varied with different air-masses; in the case of southern air-masses, external sources dominated the PM2.5 concentrations in Beijing and local contributions decreased rapidly; in contrast, in the case of northwestern air-masses, the opposite pattern occurred. Overall, the contribution of local sources to PM2.5 concentrations in Beijing varied from 16.5% to 69.3% during the monitored pollution episodes.

Chemical characteristics, sources, and formation mechanisms of PM2.5 before and during the Spring Festival in a coastal city in Southeast China

Severe pollution caused by atmospheric particulate matter (PM) has become a global environmental issue. Samples of atmospheric PM were collected before and during the Chinese Spring Festival in Xiamen, a coastal city in Southeast China, to investigate their chemical characteristics, sources, and formation mechanisms. The results indicated that PM2.5 mass concentrations comprised 53.60% and 56.31% of total suspended particulates before and during the Spring Festival, respectively. Due to the halt of factory production and construction and the reduction of vehicle flow during the Spring Festival, the concentrations of organic carbon, elemental carbon and water soluble ions in PM2.5 decreased by 78.56%, 84.19% and 27.53%, respectively, compared with those before the Spring Festival. However, the concentrations of K+, Mg2+, Al, Sr, and Ba increased by 3121.76%, 571.67%, 183.71%, 180.15%, and 137.58%, respectively, resulting from the display of fireworks and firecrackers during the Spring Festival. Analysis of backward air mass trajectory indicated that the concentrations of PM2.5 and its components were dominated by local pollution sources before and during the Spring Festival. The relationships between meteorological conditions and pollutant concentrations showed that the secondary organic aerosol was generated from the heterogeneous reaction before the Spring Festival, and the secondary inorganic aerosol was formed by the photochemical reaction during the Spring Festival.

광주 지역에서 2015년 10월에 발생한 PM2.5 고농도 사례 특성 분석

A severe haze event occurred in October 2015 in Gwangju, Korea. In this study, the driving chemical species and the formation mechanisms of PM2.5 pollution were investigated to better understand the haze event. Hourly concentrations of PM2.5, organic and elemental carbon, water-soluble ions, and elemental constituents were measured at the air quality intensive monitoring station in Gwangju. The haze event occurred was attributed to a significant contribution (72.3%) of secondary inorganic species concentration to the PM2.5, along with the contribution of organic aerosols that were strongly attributed to traffic emissions over the study site. MODIS images, weather charts, and air mass backward trajectories supported the significant impact of long-range transportation (LTP) of aerosol particles from northeastern China on haze formation over Gwangju in October 2015. The driving factor for the haze formation was stagnant atmospheric flows around the Korean peninsula, and high relative humidity (RH) promoted the haze formation at the site. Under the high RH conditions, SO₄2- and NO₃- were mainly produced through the heterogenous aqueous-phase reactions of SO₂ and NO₂, respectively. Moreover, hourly O₃ concentration during the study period was highly elevated, with hourly peaks ranging from 79 to 95 ppb, suggesting that photochemical reaction was a possible formation process of secondary aerosols. Over the PM2.5 pollution, behavior and formation of secondary ionic species varied with the difference in the impact of LTP. Prior to October 19 when the influence of LTP was low, increasing rate in NO3- was greater than that in NO₂, but both SO₂ and SO₄2- had similar increasing rates. While, after October 20 when the impact of haze by LTP was significant, SO₄2- and NO₃- concentrations increased significantly more than their gaseous precursors, but with greater increasing rate of NO₃-. These results suggest the enhanced secondary transformation of SO₂ and NO₂ during the haze event. Overall, the result from the study suggests that control of anthropogenic combustion sources including vehicle emissions is needed to reduce the high levels of nitrogen oxide and NO₃- and the high PM2.5 pollution occurred over fall season in Gwangju.

Characteristics of the secondary water-soluble ions in a typical autumn haze in Beijing

Four haze episodes (EPs) were observed in October 2014 in Beijing, China. For better understanding of the characteristics and the formation mechanisms of PM2.5 (particulate matter with an aerodynamic diameter ≤ 2.5 μm), especially secondary water-soluble inorganic species in these haze events, hourly concentrations of PM2.5, sulfate, nitrate, and ammonium (SNA) were measured in this study. Concentrations of gaseous pollutants and meteorological parameters were also measured. The average concentration of PM2.5 was 106.6 ± 83.5 μg m−3, which accounted for around 53% of PM10 (particulate matter with an aerodynamic diameter ≤ 10 μm) mass. Nitrogen dioxide (NO2) concentration was much higher than that of sulfur dioxide (SO2) since October is a non-heating month. SNA is the most abundant secondary water-soluble inorganic species and contributed to 33% of PM2.5 mass concentration. Sulfur oxidation ratio (SOR) was much higher than nitrogen oxidation ratio (NOR). NOR and SOR increased with elevated PM2.5 levels and heterogeneous processes seemed to be the most plausible explanation of this increase. Relative humidity (RH), which is of great influence on aerosol liquid water content (ALWC), played a considerable role in the formation of secondary inorganic aerosols, accelerated the secondary transformation of gaseous precursors, and further aggravated haze pollution. The positive feedback loop associated with high aerosol levels and low planetary boundary layer (PBL) height led to the evolution and exacerbation of heavy haze pollution. Fire maps and 48-h air mass backward trajectories supported the significant impact of biomass burning activities and regional transport on haze formation over Beijing in October 2014.

Participating patterns of trace elements in PM2.5 formation during iron ore sintering process

Patterns of trace elements participating in PM2.5 (aerosol dynamic diameter ≤2.5 μm) formation during iron ore sintering process were investigated. For elucidating this property, PM2.5 collected from before and after the flue-gas-temperature-rising point (stage-1 and stage-2) was examined. The results show that trace elements including Pb, K, Na, Cl and S presented an enriched tendency in PM2.5 from stage-2, while characterised lower contents in PM2.5 from stage-1. Owing to the tiny size of PM2.5, trace elements participated in the formation of Fe-rich and Fe–Al–Si-rich particles in heterogeneous manner. Moreover, S participated in the formation of CaSO4 particles from stage-1 and stage-2 in the form of homogeneous pattern, while Pb, K, Na and Cl participated homogeneously in the form of hybrid PbCl2–KCl, KCl and NaCl particles only from stage-2. The finding results clearly showed the relationship between the formation mechanisms of PM2.5 and the contribution of trace elements, which can serve as the guideline to control PM2.5 in sintering plants.

Satellite observational study on correlations among aerosol optical depth, NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and SO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; over China

Secondary aerosol contributes significantly to particulate air pollution in China which has become an increasely serious threat to the public health and the economic development. Nitrogen dioxide (NO2) and sulfur dioxide (SO2) are two of the most important precursors to secondary inorganic aerosol. To study the relations between atmospheric aerosol and NO2 and SO2 is helpful to reveal the source and the formation mechanism of PM2.5 (particulate matter with an aerodynamic diameter less than 2.5 μ m) in China.

Synthesizing scientific progress: outcomes from U.S. EPA's carbonaceous aerosols and source apportionment STAR grants.

In response to recommendations by the National Research Council in the late 1990 s and early 2000s for critical research into understanding sources and formation mechanisms of PM2.5, EPA created multiple funding opportunities through the Science to Achieve Results (STAR) program: "Measurement, Modeling, and Analysis Methods for Airborne Carbonaceous Fine Particulate Matter" (2003) and "Source Apportionment of Particulate Matter" (2004). The carbonaceous fine PM solicitation resulted in 16 different projects focusing on the measurement methods, source identification, and exploration of the chemical and physical processes important for PM2.5 carbon in the atmosphere. The source apportionment funding opportunity led to 11 projects improving tools and characterization of source-receptor relationships of PM2.5. Many funding mechanisms include a final synopsis of funded research and published manuscripts. Here, this evaluation is extended to include citations of research published as part of these solicitations. These solicitations resulted in 275 publications that included more than 850 unique authors in 37 different journals with a weighted average 2011 impact factor of 4.21. At the time of this assessment, these publications have been cited by 13,612 peer review journal articles with 31 (11%) of the manuscripts being cited over 100 times.