Fine particles at a background site in Central France: Chemical compositions, seasonal variations and pollution events

Investigation of RH effect on uncommon limonene ozonolysis products and SOA formation in indoor air with real time measurement techniques

Scientific interest in SOA influence on indoor air quality increases since last 20 years. It is well known, that particles of nano-sized diameter pose a threat for human health causing, among others: eye, upper airway irritation, inflammatory response in cells, worsening asthma, hypertension, diabetes, and central nervous dysfunction. Terpenes are reactive VOCs, commonly emitted in indoor air and considered to be SOA precursors by oxidation reactions. The aim of this study was to investigate the relative humidity influence on i) formation of limonene ozonolysis products and ii) SOA formation process - especially the first steps of it. We managed to determine 4 uncommon limonene ozonolysis products (m/z: 43, 83, 99 and 110) appearing in the PTR-TOF-MS mass spectra with the same frequency as well-known formaldehyde, acetone, acetic acid and formic acid. We also detected m/z 75 and m/z 115 formed under dry conditions and m/z 111 and m/z 125 formed under humid conditions. Detected masses formula is proposed with probability >70 % and the probability is derived from the deviation of the exact mass to the measured one and the isotope distribution. SMPS data analysis allowed us to conclude that RH around 40% increases particle mass concentration, regardless initial limonene concentration. Unfortunately, conclusions about RH influence on particle number concentration are inconsistent. Under low initial terpene concentration, RH around 40% decreases particle number concentration. However, for high initial limonene concentration, RH around 40% caused increase in particle number concentration. Obtained results allowed to conclude, that i) RH influences both particle number and particle mass concentration, ii) initial substrate concentration influences SOA formation altering the RH effect, iii) comparison of results and drawing conclusions is difficult due to different experimental protocols in the literature and due to the number of factors influencing SOA formation initiated by terpene oxidation.

Chemical characterization of water-soluble ions in highly time-resolved atmospheric fine particles in Istanbul megacity

The diurnal and seasonal variations of water-soluble ions (WSIs) in fine particles were investigated in an area predominantly affected by traffic emissions in Beşiktaş, Istanbul between 2017 and 2018. PM_2.5 samples were collected at high time resolutions of 2 h during the daytime and 12 h during the nighttime for six sampling campaigns over all seasons. Five inorganic water-soluble ions (SO₄^2-, NH₄⁺, NO₃^-, PO₄^-3, and NO₂^-) were determined using ion chromatography. Source analysis was investigated with principal component analysis (PCA) and bivariate polar plots. In descending order, WSIs concentrations were SO₄^2->NH₄⁺> NO₃^-> PO₄^-3>NO₂^- during the different seasons. The high time-resolved concentrations ranged as follows: sulfate 1.2-1118.1, ammonium 0.3-289.9, phosphate 2.9-107.6, nitrate 4.6-179.7, and nitrite 0.8-9.0 ng/m³, with yearly averages of 226.5, 59.0, 58.4, 37.9, and 3.3 ng/m³, respectively. Except for phosphate, all WSIs had strong seasonal variations with high concentrations during the winter and low concentrations during the summer. Molar ratios revealed that the formation of ammonium sulfate was less likely than ammonium nitrate. Principal component analysis resolved secondary aerosols (43.9%), residential heating (34.6%), shipping emissions (8.7%), and vehicle emissions (6.7%) as the major sources of WSIs, OC, EC, and PM_2.5 in Beşiktaş, Istanbul. Sulfate aerosol originated mainly from two nearby areas, SW and NE, of the sampling site tentatively due to residential heating and shipping emissions, respectively.

Effect of relative humidity on SOA formation from aromatic hydrocarbons: Implications from the evolution of gas- and particle-phase species

Relative humidity (RH) plays a significant role in secondary organic aerosol (SOA) formation, but the mechanisms remain uncertain. Using a 30 m³ indoor smog chamber, the influences of RH on SOA formation from two conventional anthropogenic aromatics (toluene and m-xylene) were investigated from the perspective of both the gas- and particle- phases based on the analysis of multi-generation gas-phase products and the chemical composition of SOA, which clearly distinguishes from many previous works mainly focused on the particle-phase. Compared to experiments with RH of 2.0%, SOA yields increased by 11.1%-133.4% and 4.0%-64.5% with higher RH (30.0%-90.0%) for toluene and m-xylene, respectively. The maximum SOA concentration always appeared at 50.0% RH, which is consistent with the change trend of SOA concentration with RH in the summertime field observation. The most plausible reason is that the highest gas-phase OH concentration was observed at 50.0% RH, when the increases in gas-phase OH formation and OH uptake to aerosols and chamber walls with increasing RH reached a balance. The maximum OH concentration was accompanied by a notable decay of second-generation products and formation of third-generation products at 50.0% RH. With further increasing RH, more second-generation products with insufficient oxidation degree will be partitioned into the aerosol phase, and the aqueous-phase oxidation process will also be promoted due to the enhanced uptake of OH. These processes concurrently caused the O/C and oxidation state of carbon (OSc) to first increase and then slightly decrease. This work revealed the complex influence of RH on SOA formation from aromatic VOCs through affecting the OH concentration, partitioning of advanced gas-phase oxidation products as well as aqueous-phase oxidation processes. Quantitative studies to elucidate the role of RH in the partitioning of oxidation products should be conducted to further clarify the mechanism of the influence of RH on SOA formation.

Spatio-temporal analysis of urban air pollutants throughout China during 2014-2019

Air pollution control has become the top priority of China's "green development" concept since 2013. The Chinese government has enacted a range of policies and statutes to control contaminant emissions and improve air quality. On the basis of the national air quality ground observation database, the spatial and temporal distribution of air quality index value (AQI), fine particulate matter (PM_2.5), coarse particles (PM₁₀), sulfur dioxide (SO₂), nitrogen dioxide (NO₂), carbon monoxide (CO), and ozone (O₃) were explored in 336 cities throughout China from 2014 to 2019. AQI and most pollutants (except O₃) decreased in concentrations from 2014 to 2019. In 2019, all cities except Henan reached the level 2 of the ambient air quality index, and six cities had a lower ambient air quality index and reached the level 1. Spatially, higher pollutant concentrations were concentrated in large city clusters, whereas the areas with high O₃ concentration were found across the country. Furthermore, central heating was shown to have a negative impact on air quality. The observed AQI value, PM_2.5, PM₁₀, SO₂, NO₂, and CO concentrations were highest in north and northwest China and Henan province in central China. The correlations among pollutants suggest that the main sources of pollutants are fossil fuel combustion, industrial production, and motor vehicle emissions. The influence of meteorological factors on air quality, long-distance transportation, and the transformations of pollutants should be explored in future research.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11869-021-01043-5.

Quantification of the impact of port activities on PM10 levels at the port-city boundary of a mediterranean city

The main objective of this work was to quantify the impact of handling of bulk materials on PM₁₀ levels measured at the port-city border of Alicante (Spain), located on the western Mediterranean coast. To achieve that goal, 355 PM₁₀ samples were collected at the perimeter of the harbor of Alicante from March 2017 to February 2018. A 181 sample subgroup was chemically characterized in order to perform a source apportionment study with the EPA PMF 5.0 model. Eight factors were identified, two of them directly related to the handling of bulk materials (Limestone + gypsum and Clinker), accounting jointly for 35% of the average PM₁₀ concentration. A Road traffic factor was the second highest contributor to PM₁₀ levels (17%) while the Shipping emissions factor accounted for only 6% of the average PM₁₀ mass. Other factors such as Biomass burning+ secondary nitrate and Aged sea salt represented a joint contribution of 25% of the PM₁₀ mass. Results indicate that emission abatement strategies should primarily focus on the reduction of fugitive emissions caused by the handling of bulk materials at the docks. Moreover, scenarios including reductions of more than 50% in bulk handling sources and 10% in other anthropogenic sources would help to reduce anthropogenic exceedances of the daily PM₁₀ limit (50 μg·m^-3) and to approach to WHO daily PM₁₀ standard (20 μg m^-3).

Temporal and Spatial Variation of PM2.5 in Xining, Northeast of the Qinghai–Xizang (Tibet) Plateau

PM2.5 was sampled from January 2017 to May 2018 at an urban, suburban, industrial, and rural sites in Xining. The annual mean of PM2.5 was highest at the urban site and lowest at the rural site, with an average of 51.5 ± 48.9 and 26.4 ± 17.8 μg·m−3, respectively. The average PM2.5 concentration of the industrial and suburban sites was 42.8 ± 27.4 and 37.2 ± 23.7 μg·m−3, respectively. All sites except for the rural had concentrations above the ambient air quality standards of China (GB3095-2012). The highest concentration of PM2.5 at all sites was observed in winter, followed by spring, autumn, and summer. The concentration of major constituents showed statistically significant seasonal and spatial variation. The highest concentrations of organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and water-soluble inorganic ions (WSIIs) were found at the urban site in winter. The average concentration of F− was higher than that in many studies, especially at the industrial site where the annual average concentration of F− was 1.5 ± 1.7 μg·m−3. The range of sulfur oxidation ratio (SOR) was 0.1–0.18 and nitrogen oxidation ratio (NOR) was 0.02–0.1 in Xining. The higher SO42−/NO3− indicates that coal combustion has greater impact than vehicle emissions. The results of the potential source contribution function (PSCF) suggest that air mass from middle- and large-scale transport from the western areas of Xining have contributed to the higher level of PM2.5. On the basis of the positive matrix factorization (PMF) model, it was found that aerosols from salt lakes and dust were the main sources of PM2.5 in Xining, accounting for 26.3% of aerosol total mass. During the sandstorms, the concentration of PM2.5 increased sharply, and the concentrations of Na+, Ca2+ and Mg2+ were 1.13–2.70, 1.68–4.41, and 1.15–5.12 times higher, respectively, than annual average concentration, implying that aerosols were mainly from dust and the largest saltwater lake, Qinghai Lake, and many other salt lakes in the province of Qinghai. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was utilized to study the surface components of PM2.5 and F− was found to be increasingly distributed from the surface to inside the particles. We determined that the extremely high PM2.5 concentration appears to be due to an episode of heavy pollution resulting from the combination of sandstorms and the burning of fireworks.

PM events and changes in the chemical composition of urban aerosols: A case study in the western Mediterranean

More than 400 PM₁ and 400 PM₁₀ daily samples were collected in the urban center of Elche (close to the Spanish Mediterranean coast) from February 2015 to February 2018. Samples were analyzed to determine the concentrations of major and trace components with the aim of evaluating the influence of specific pollution events on the chemical composition of both PM fractions. The concentrations of crustal elements in PM₁₀ significantly increased during Saharan dust outbreaks, particularly titanium, which has been identified as a good tracer of these events in the study area. Sulfate and nitrate levels were also enhanced due to secondary aerosol formation on mineral dust particles. Local pollution episodes had a great impact on submicron nitrate, whose mean concentration was more than four times higher than on non-event days. The chemical mass closure method was used to reconstruct PM₁ and PM₁₀ concentrations. Reasonably good correlations between measured and reconstructed concentrations were obtained, except for PM₁₀ samples collected during Saharan dust events. This was due to the underestimation of the dust contribution during these episodes. Moderate differences in the average chemical composition of PM₁₀ were observed between event and non-event days. Regarding PM₁, only local pollution episodes had a certain impact on its chemical composition.

Chemistry-triggered events of PM2.5 explosive growth during late autumn and winter in Shanghai, China

To better understand the mechanism of PM_2.5 explosive growth (EG), we conducted concurrent measurements of gaseous pollutants, PM_2.5 and its chemical composition (inorganic ions, organic carbon, and element carbon) with a time resolution of 1 h in Shanghai in late autumn and winter from 2014 to 2017. In this study, the EG events, which are defined as the net increase in the mass concentration of PM_2.5 by more than 100 μg m^-3 within hours, are separately discussed for 3, 6, or 9 h. The number of EG events decreased from 19 cases in 2014 to 6 cases in 2017 and the corresponding PM_2.5 concentration on average decreased from 183.6 μg m^-3 to 128.8 μg m^-3. Both regional transport and stagnant weather (windspeed < 2.0 m s^-1) could lead to EG events. The potential source contribution function (PSCF) shows that the major high-pollution region is in East China (including Zhejiang, Jiangsu, Shandong, and Anhui Province) and the North China Plain. The contribution of stagnant conditions to EG episode hours of 55% (198 h, 156.9 μg m^-3) is higher than that of regional transport (45%, 230 h, 163.0 μg m^-3). To study the impact of local emission, chemical characteristics and driving factors of EG were discussed under stagnant conditions. The major components contributing to PM_2.5 are NO₃^- (17.9%), organics (14.1%), SO₄^2- (13.1%), and NH₄⁺ (13.1%). The driving factors of EG events are the secondary aerosol formation of sulfate and nitrate and primary emissions (vehicle emissions, fireworks, and biomass burning), but the secondary transformation contributes more to EG events. The formation of sulfate and nitrate is dominated by gas-phase oxidation and heterogeneous reactions, which are enhanced by a high relative humidity. The current study helps to understand the chemical mechanism of haze and provides a scientific basis for air pollution control in Shanghai.

Comprehensive hippocampal metabolite responses to PM2.5 in young mice

Fine particulate matter (PM_2.5) exposure alters brain development, clinical cognition and behavior in childhood. Previous studies of this subject have mainly been epidemiological investigations or analyses of gene and protein levels; however, gas chromatography-mass spectrometry (GC-MS)-based metabolic profiling, which will help clarify the molecular mechanisms of susceptibility in PM_2.5-induced neurotoxicity, is lacking. In the present study, C57BL/6 mice at different ages (4 weeks, 4 months and 10 months) received oropharyngeal aspiration of PM_2.5 (3 mg/kg) every other day for 4 weeks. The Morris water maze showed that PM_2.5 exposure caused deterioration of spatial learning and memory in young (4 week old) mice. In addition, the levels of several metabolites belonging to different metabolite classes were significantly changed by PM_2.5 exposure in 4-week-old mice. Based on metabolic pathway analysis, we speculated that the decline in spatial learning and memory due to PM_2.5 exposure may be directly or indirectly associated with hippocampal region-specific metabolic alterations involving energy metabolism (citric acid, succinic acid, malic acid, maltose and creatinine); cholesterol metabolism (desmosterol, lanosterol and campesterol); arachidonic acid metabolism (methyl arachidonic acid, nonanoic acid and linoleic acid); inositol phosphate metabolism (myo-inositol, myo-inositol-1-phosphate and methyl-phosphate) and aspartic acid metabolism (aspartic acid, asparagine and homoserine).