Characterization of carbonaceous particles by single particle aerosol mass spectrometer in the urban area of Chengdu, China.

Carbonaceous particles are an important chemical component of atmospheric fine particles. In this study, a single particle aerosol mass spectrometer was used to continuously measure the carbonaceous particles in Chengdu, one of the megacities most affected by haze in China, from January 22 to March 3, 2021. During the observation period, the average mass concentration of PM2.5 was 62.3 ± 37.2 µg m-3, and the emissions from mobile sources were more prominent. Carbonaceous particles accounted for 68.6% of the total particles and could be classified into 10 categories, with elemental carbon (EC) mixed with sulfate (EC-S) particles making the highest contribution (33.1%). EC particles rich in secondary components and organic carbon (OC) particles rich in secondary component exhibited different diurnal variations, suggesting different sources and mixing mechanisms. From "excellent" to "polluted" days, the contributions of EC-S, EC mixed with sulfate and nitrate (EC-SN) and OC mixed with EC (OC-EC) particles increased by 9.8%, 4.5% and 6.6%, respectively, and thus these particles are key targets for future pollution control. The potential source contribution of the southwest area was stronger than that of other areas, and the potential contribution of regional transport to EC-related particles was stronger than to OC-related particles. Most particles were highly mixed with sulfate or nitrate, and the level of secondary mixing further enhanced as pollution worsened.

[Characteristics of Carbonaceous Species in PM2.5 in Chengdu Under the Background of Emission Reduction].

The Air Pollution Prevention and Control Action Plan and Three-year Plan on Defending the Blue Sky promulgated by the State Council of the People's Republic of China have played an important role in the overall improvement of air quality in China. However, few studies have evaluated the implementation effects of these two policies in Sichuan Basin and the new characteristics of PM2.5 chemical components after the implementation of these policies. The key periods for evaluating the implementation effects of these two pollution reduction policies are 2017 and 2020, respectively. In order to study the atmospheric PM2.5 and carbonaceous species in Chengdu during these two periods, this study sampled the PM2.5 in Chengdu from October 2016 to July 2017 and December 2020, respectively, and the organic carbon (OC) and elemental carbon (EC) were analyzed. The results showed that the annual ρ(PM2.5) from 2016-2017 in Chengdu was (114.0±76.4) µg·m-3. The maximum value of the ρ(PM2.5) appeared in winter[(193.3±98.5) µg·m-3], and the minimum value appeared in spring[(73.8±32.3) µg·m-3]. By contrast, the ρ(PM2.5) in winter decreased significantly in 2020, with a value of (96.0±39.3) µg·m-3. The annual ρ(OC) and ρ(EC) from 2016-2017 were (21.1±16.4) µg·m-3 and (1.9±1.3) µg·m-3, which accounted for 18.5% and 1.7% of the PM2.5 mass, respectively. The seasonal variation characteristic of ρ(OC) was:winter[(40.6±21.5) µg·m-3]>autumn[(17.0±7.0) µg·m-3]>summer[(14.4±3.9) µg·m-3]>spring[(12.6±6.0) µg·m-3], whereas the ρ(EC) in the four seasons were close, ranging from 1.3 to 2.4 µg·m-3. The annual ρ(SOC) was (9.4±9.1) µg·m-3, which accounted for 44.5% of the OC mass. Compared with that in winter 2016, the ρ(OC) decreased by 52.7% in winter 2020, whereas the ρ(EC) increased by 26.1%. With the aggravation of pollution, the change trends of carbon species and their contributions were different. Compared with that in winter 2016, the variation in the contribution of OC with the aggravation of pollution in winter 2020 was more stable, whereas the proportion of SOC increased more obviously. There were obvious differences in the direction of air masses and the potential source area of pollutants in each season. Although there was no significant change in the direction of air masses in winter 2020 compared with those in winter 2016, the pollutant concentrations corresponding to each cluster decreased significantly, and the potential source area of pollutants expanded significantly to the eastern area.

Laurionite Competes with 2D Ruddlesden-Popper Perovskites During the Saturation Recrystallization Process.

The room-temperature saturation recrystallization (RTSR) method has been extensively used to prepare all-inorganic lead halide perovskite (e.g., CsPbBr3) nanocrystals. Here, we revealed that the composition of the products prepared by the seemingly simple RTSR method could be extremely complex under different experimental parameters. The pH value of the solution and the protonation tendency of the amines influenced by the amounts and types of introduced amines, oleic acid, and water from the environment determined the composition of the final products. PbBr2, 2D Ruddlesden-Popper perovskites (RPPs) formed by perovskite layers separated by intercalating cations, and laurionite Pb(OH)Br would form under acidic, mildly acidic, and alkaline conditions, respectively. Based on the understanding of the formation mechanism, Pb(OH)Br microparticles with well-defined morphologies were prepared, which could be transformed into highly luminescent CH3NH3PbBr3 with the morphology unchanged. The protonated amine behaves as an intercalating layer during the formation of 2D RPPs. Phenylethylamine (PEA) was proven to be an appropriate amine to prepare pure RPP microplates because of its weaker alkalinity compared to aliphatic amines. The prepared (PEA)2PbBr4 RPP microplates showed strong deep-blue light emission with a PL peak at 415 nm, which could be fine-tuned by changing amines. This study proved the complex reaction pathways of the seemingly simple RTSR method and extended the RTSR method into the fabrication of 2D RPPs and laurionite with promising applications in optoelectronic devices.

Ultrastable Laurionite Spontaneously Encapsulates Reduced-dimensional Lead Halide Perovskites.

Reduced dimensional lead halide perovskites (RDPs) have attracted great research interest in diverse optical and optoelectronic fields. However, their poor stability is one of the most challenging obstacles prohibiting them from practical applications. Here, we reveal that ultrastable laurionite-type Pb(OH)Br can spontaneously encapsulate the RDPs in their formation solution without introducing any additional chemicals, forming RDP@Pb(OH)Br core-shell microparticles. Interestingly, the number of the perovskite layers within the RDPs can be conveniently and precisely controlled by varying the amount of CsBr introduced into the reaction solution. A single RDP@Pb(OH)Br core-shell microparticle composed of RDP nanocrystals with different numbers of perovskite layers can be also prepared, showing different colors under different light excitations. More interestingly, barcoded RDP@Pb(OH)Br microparticles with different parts emitting different lights can also be prepared. The morphology of the emitting microstructures can be conveniently manipulated. The RDP@Pb(OH)Br microparticles demonstrate outstanding environmental, chemical, thermal, and optical stability, as well as strong resistance to anion exchange processes. This study not only deepens our understanding of the reaction processes in the extensively used saturation recrystallization method but also points out that it is highly possible to dramatically improve the performance of the optoelectronic devices through manipulating the spontaneous formation process of Pb(OH)Br.

Characteristics, evolution, and regional differences of biomass burning particles in the Sichuan Basin, China.

The Sichuan Basin has experienced serious air pollution from fine particulate matter (PM2.5) in the past few years with biomass burning has been identified as a major source of PM2.5 in this region. We used single particle aerosol mass spectrometer to investigate the characteristics of biomass burning particles in three interacting cities representing different types of urban environment in the Sichuan Basin. A total of 739,794, 279,610, and 380,636 biomass burning particles were detected at Ya'an, Guang'an, and Chengdu, which represented 42%, 69%, and 61%, respectively, of the total number of particles. We analyzed the chemical composition, transportation, and evolution of biomass burning particles. The contribution of K-elemental carbon and K-secondary inorganic particles was highest in Ya'an (36%) and Guang'an (47%), respectively, reflecting the important role of fresh biomass burning particles and long-distance transport in these two cities. Air masses originating from different directions corresponded to different levels of PM2.5 and the contributions of polluted clusters increased significantly on polluted days. Fresh and secondary inorganic biomass burning particles increased pollution at Ya'an and Guang'an, respectively, but dominated different stages of pollution in Chengdu. K-nitrate particles were formed by photochemical reactions, whereas K-sulfate particles were formed by both photochemical and liquid-phase reactions. Investigation of the degree of particle aging showed that there were more fresh particles at Ya'an and more aged particles at Guang'an. These results are useful in helping our understanding of the characteristics of biomass burning particles and evaluating their role in PM2.5 pollution in the Sichuan Basin.

Template-Confined Site-Specific Electrodeposition of Nanoparticle Cluster-in-Bowl Arrays as Surface Enhanced Raman Spectroscopy Substrates.

Nanoparticle clusters have important applications in plasmonics and optical sensing fields. Various methods have been used to construct nanoparticle clusters, represented by assembling preprepared nanoparticles using DNA. However, preparation of nanoparticle clusters using a one-step method is still challenging. Herein, by using prepatterned microscale bowls as individual reaction containers, clusters of Au nanoparticles with a homogeneous structure are electrodeposited at the bottom of each bowl. The structure of the nanoparticle clusters can be simply manipulated by varying electrodeposition parameters. After coating these Au nanoparticle cluster-in-bowl arrays with a thin layer of Ag film, they can be used as surface enhanced Raman spectroscopy (SERS) substrates with an SERS enhancement factor of ∼108. Importantly, the concave bowl structures can facilitate delivery of the analytes into the crevices between the bowls and the nanoparticle clusters where SERS "hot spots" (or sensitive sites) are located. The crevices with a gradually changed gap distance between the concave bowl structure and the nanoparticle clusters are excellent traps for catching and SERS sensing of biospecies with varied sizes (e.g., viruses and proteins). We demonstrated sensitive SERS detection of viruses and proteins using the nanoparticle-cluster-in-bowl SERS substrates. This technique has the ability to control the resulting structure at specific locations with electrodeposited materials, which enables new opportunities for assembling complex surface patterns with diverse applications in optical and plasmonic fields.

Chemical characterization of submicron aerosol particles during wintertime in a northwest city of China using an Aerodyne aerosol mass spectrometry.

An Aerodyne quadrupole aerosol mass spectrometry (Q-AMS) was utilized to measure the size-resolved chemical composition of non-refractory submicron particles (NR-PM1) from October 27 to December 3, 2014 at an urban site in Lanzhou, northwest China. The average NR-PM1 mass concentration was 37.3 µg m-3 (ranging from 2.9 to 128.2 µg m-3) under an AMS collection efficiency of unity and was composed of organics (48.4%), sulfate (17.8%), nitrate (14.6%), ammonium (13.7%), and chloride (5.7%). Positive matrix factorization (PMF) with the multi-linear engine (ME-2) solver identified six organic aerosol (OA) factors, including hydrocarbon-like OA (HOA), coal combustion OA (CCOA), cooking-related OA (COA), biomass burning OA (BBOA) and two oxygenated OA (OOA1 and OOA2), which accounted for 8.5%, 20.2%, 18.6%, 12.4%, 17.8% and 22.5% of the total organics mass on average, respectively. Primary emissions were the major sources of fine particulate matter (PM) and played an important role in causing high chemically resolved PM pollution during wintertime in Lanzhou. Back trajectory analysis indicated that the long-range regional transport air mass from the westerly was the key factor that led to severe submicron aerosol pollution during wintertime in Lanzhou.

[Changing characteristics of the main air pollutants of the Dongling Mountain in Beijing].

Concentrations of SO2, NO(x), O3 and PM2.5 were observed from August 2009 to June 2011 in Beijing forest ecology observation site which locates at the Dongling Mountain of Beijing. Monthly, seasonal variation and statistical diurnal variation characteristics of air pollutants were analyzed. Besides, the influence of transportation to air pollutants was also discussed combined with the back trajectories of air mass. The average concentrations of NO, NO2, NO(x), O3, SO2 and PM2.5 were (2.0 +/- 1.6), (13.2 +/- 7.2), (15.3 +/- 8.2), (61.0 +/- 19.6), (3.6 +/- 3.6) and (35.6 +/- 32.0) microg x m(-3), respectively. The concentration of pollutants in Beijing forest ecology observation site was lower than that in rural observation site in Beijing. The highest value of NO(x) appeared in autumn while the lowest appeared in summer, and concentrations of NO(x) in autumn and summer were (17.0 +/- 8.0) microg x m(-3) and (13.8 +/- 4.1) microg x m(-3), respectively. Concentrations of O3 in spring and summer were higher than those in autumn and winter. The highest concentration of O3 appeared in June. The concentration of SO2 in winter was the highest, and this concentration was 2.7 times to the lowest concentration in summer. The highest concentration of PM2.5 appeared in summer and was 56.4 microg x m(-3). There were obvious diurnal variation of NO(x), O3 and SO2. There are two peaks of NO(x) have been observed, however there are only one peak of O3 and SO2 has been observed. There was no obvious diurnal variation of PM2.5 to other pollutants.