Journal of Atmospheric Chemistry最新文献

Particulate matter (PM) can affect climate, air quality, human health, acid deposition and visibility, and contain a significant fraction of organic (OC) and elemental carbon (EC). Southern Africa is an important source region for OC and EC, however, little OC and EC data have been published for this region. This paper presents a multi-year, multi-site (an urban-industrial site in the Vaal Triangle, UI-VT; an industrially influenced site at Amerfoort, iI-AF; and two regional background sites at Skukuza and Louis Trichardt, RR-SK and RR-LT) PM with an aerodynamic diameter?≤?2.5?μm (PM_2.5) OC and EC dataset for South Africa. The median OC (9.3) and EC (3.2?μg.m^?3) concentrations at UI-VT were 1.3 to 2.5 and 2.7 to 4.4 times higher, if compared to the other sites. OC/EC ratios indicated that sources in close proximity to UI-VT were likely the main contributors, while sources that are more distant contributed fractionally more at the other sites. Household combustion for space heating and regional open biomass burning contributed to elevated levels during the cold and dry months at UI-VT. Regional open biomass burning also lead to higher OC and EC concentrations during the dry season at the industrially influenced site (iI-AF) and one of the regional background sites (RR-SK). From the seasonal concentration patterns, it seemed as if household combustion for space heating also contributed at these two sites during the cold months, but this could not be proven, even if only samples with limited influence of open biomass burning were considered. Such biomass burning influences were semi-quantified by considering MODIS fire pixels occurring within the air mass fetch region for each sample. For the remaining regional background site (RR-LT) the results suggesed that only regional open biomass burning contributed to elevated levels of OC and EC in the dry season and that household combustion for space heating did not contribute significantly.

The rapid economic development and significant expansion of urban agglomerations in China have resulted in issues associated with haze and photochemical smog. Central China, a transitional zone connecting the eastern coast and western interior, suffers from increasing atmospheric pollution. This study performed a spatio-temporal analysis of fine particulate matter (PM_2.5) pollution in Changsha, a provincial capital located in central China. Samples of PM_2.5 were collected at five different functional areas from September 2013 to August 2014. The PM_2.5 concentration at the five sampling sites was the highest in winter and the lowest in summer, with an average annual PM_2.5 concentration of 105.2?±?11.0?μg/m³. On average, residential sites had the highest concentrations of PM_2.5 while suburban sites had the lowest. We found that inorganic ionic species were dominant (~48%), organic species occupied approximately 25%, whereas EC (~3.7%) contributed insignificantly to the total PM_2.5 mass. Ion balance calculations show that the PM_2.5 samples at all sites were acidic, with increased acidity in spring and summer compared with autumn and winter. Air quality in Changsha is controlled by four major air masses: (1) Wuhan and the surrounding urban clusters, (2) the Changsha-Zhuzhou-Xiangtan urban agglomeration and the surrounding cities, and (3) southern and (4) eastern directions. The north–south transport channel is the most significant air mass trajectory in Changsha and has a significant impact on PM_2.5 pollution.

Real-time simultaneous measurements of rainwater and PM₁₀ chemistry were carried out at Delhi during the year 2016–17 in order to assess the levels of carbonaceous species and their wet scavenging during monsoon and non-monsoon seasons at Delhi. The PM₁₀ samples were collected Before Rain (BR), During Rain (DR) and After Rain (AR) events, while rainwater samples collected on an event basis. The ambient OC levels were always higher than the levels of EC during both monsoon and non-monsoon seasons in ambient aerosol as well as in rainwater. On an average, during rain (DR) 30% of OC aerosols and 28.2% of EC aerosols removed via wet scavenging process. In after rain (AR), 26.2% OC and 1.8% EC aerosols further decreased in comparison to DR samples due to the presence of OC and EC free air parcel. Overall it observed that the OC concentration significantly lowered from BR to DR and AR. However, EC concentrations in AR were found to be higher than DR samples indicating their build-up after the rains. The Scavenging Ratios (SRs) of OC and rain intensity had a significant positive correlation, whereas the SRs of EC showed a weak correlation with rain intensity. The SRs of EC were significantly higher during non-monsoon as compared to monsoon season. Such characteristics can be explained based on the particles size, source and the hygroscopicity of both types of carbonaceous aerosol.

Optical properties of atmospheric particles at Mexico City (UNAM) and Queretaro (JQRO) were measured with a Photoacoustic Extinctiometer (PAX) at 870?nm. The Mexico City Metropolitan Area has around 21 million inhabitants and Queretaro Metropolitan Area has little more than a million. Observations of meteorological parameters (relative humidity, solar radiation, and wind speed) were used to identify the rainy and dry seasons and explain the daily and seasonal behaviors of particles optical properties. The measurements were made from November 1, 2014 to July 31, 2016. At UNAM, the mean values of the scattering coefficient (B_scat) in cold dry, warm dry, and rainy seasons were 35.8, 27.1, and 31.3?Mm^?1, respectively; while at JQRO were 10.9, 11.9, and 15.0?Mm^?1. The average values of the absorption coefficient (B_abs) at UNAM during the cold dry, warm dry, and rainy seasons were 14.5, 12.7, and 12.7?Mm^?1, respectively; whereas at JQRO were 4.9, 4.7, and 3.9?Mm^?1. Both absorption and scattering coefficients showed similar diurnal behaviors, but at UNAM they are three times higher than JQRO. Concentrations of criteria gases (O₃, NO, NO₂ and NO_x) were also measured. At UNAM no difference was observed between the seasonal values for the single scattering albedo (SSA); while in JQRO, the rainy season had the highest seasonal value, being 13% higher than in the dry seasons. The Mass Scattering Cross-Section (MSC) values at UNAM were close to 2 m²/g; on the other hand, at JQRO the MSC values were lower than 1 m²/g. The results suggest a seasonal variability in the aerosol optical properties in both sites, which should be verified with more long-term studies.

Continuous online measurements of fine particulate matter mass (PM_2.5) and its chemical composition were carried out at an urban monitoring site in Wuhan from March 2017 to February 2018. The PM_2.5 mass concentration ranged from 6.3 to 223?μg/m³, with the highest in winter and the lowest in summer. Water soluble ions (WSIs) were the most abundant component in PM_2.5 (28.8?±?22.9?μg/m³), followed by carbonaceous aerosol (11.9?±?10.4?μg/m³) and elements (5.5?±?6.7?μg/m³). It is noteworthy that six episodes of sustained high PM were observed during the study period. Five major contributors of PM_2.5 were identified by positive matrix factorization (PMF) to be the iron and steel industry, fugitive dust, secondary photochemistry, traffic-related emission and biomass burning, contributing 26.3%, 5.5%, 29.5%, 29.2% and 9.6% to PM_2.5, respectively. Furthermore, conditional probability function (CPF), trajectory analysis and potential source contribution function (PSCF) were used to identify the influences of local activities and regional source. Local sources mainly include Wuhan iron and steel group, construction sites and urban trunk roads, etc. Three pollution transport pathways of PM_2.5 in Wuhan were identified to be northwest, east and south pathway, with the relative contribution of 40%, 17% and 43%, respectively. Western Henan, northern Shaanxi and southwestern Shanxi were identified to be the major potential source regions of PM_2.5 in Wuhan.

A total of 30 precipitation samples were collected at a remote site of Qinghai Lake in the northeastern Tibetan Plateau, China, from June to August 2010. All samples were analyzed for major cations (NH₄⁺, Na⁺, K⁺, Ca²⁺, and Mg²⁺) and anions (F^?, Cl^?, NO₃^?, and SO₄^2?), electric conductivity (EC), pH, dissolved organic carbon (DOC), and oxygen isotopic composition (δ¹⁸O). The volume-weighted mean (VWM) values of pH and EC in the precipitation samples were 7.2 and 19.0?μs?cm^?1. Ca²⁺ was the dominant cation in precipitation with a VWM of 116.9 μeq L^?1 (1.6–662.9 μeq L^?1), accounting for 45.7% of total ions in precipitation. SO₄^2? was the predominant anion with a VWM of 32.7 μeq L^?1, accounting for 47.1% of the total anions. The average precipitation DOC was 1.4?mg?L^?1, and it shows a roughly negative power function with the precipitation amount. The values of δ¹⁸O in the rainwater in Qinghai Lake varied from ?13.5‰ to ?3.9‰ with an average of ?8.1‰. The enrichment factor analysis indicates that crustal materials from continental dust were the major sources for Ca²⁺ in the precipitation samples. The high concentration of Ca²⁺ in the atmosphere played an important role in neutralizing the acidity of rainwater in Qinghai Lake area. Cluster analysis of air-mass trajectories indicates that the air masses associated with northeast and east had high values of NH₄⁺, SO₄^2?, and NO₃^?, whereas large Ca²⁺ loading was related to the air mass from west.

Lightning is an important source of nitrogen oxides (LNO_x). The actual global production of LNO_x is still largely uncertain. One of the reasons for this uncertainty is the limited available observation data. We measured the concentrations of total reactive nitrogen (NO_y), nitric oxide (NO) and nitrogen dioxides (NO₂) and then obtained NO_x oxidation products (NO_z: NO_z?=?NO_y - NO_x) at a station at the top of Mount Fuji (3776?m?a.s.l.) during the summer of 2017. Increases in NO_y and NO₂ were observed on 22 August 2017. These peaks were unaccompanied by increases in CO, which suggested that the observed air mass did not contain emissions from combustion. The backward trajectories of the above air mass indicated that it moved across areas where lightning occurred. The NO_y concentration was also calculated by using a chemical transport model, which did not take NO_x produced by lightning into account. Therefore, the NO_y concentration due to lightning can be inferred by subtracting the calculated NO_y from the observed NO_y concentrations. The concentration of NO_y at 13:00 on 22 August 2017 originating from lightning was estimated to be 1.11?±?0.02 ppbv, which comprised 97?±?2% of the total NO_y concentration. The fractions of NO₂ and NO_z in the total NO_y were 0.54?±?0.01 and 0.46?±?0.03, respectively. The NO concentration was below the detection limit. We firstly observed increase of concentrations of NO_y originating from lightning by ground-based observation and demonstrated the quantitative estimates of LNO_x using model-based calculation.

In order to investigate particulate matter characteristics in the urban area of Naples, South of Italy, PM₁₀ and PM_2.5 chemical composition and properties were determined; in particular, ionic composition (Na⁺, K⁺, NH₄⁺, Mg²⁺, Ca²⁺, HCOO-, CH₃COO^?, Cl^?, NO₂^?, NO₃^?, SO₄^2?, C₂O₄^2?) and concentration of specific metals (Pb, Cd, Cu and Zn) were evaluated in association with an air masses trajectories study. Information on major ions was used to conduct the ionic balance and to evaluate sea salt and non-sea salt contributions; furthermore, the study on metals concentration allowed to distinguish the contribution of anthropic sources while their chemical behaviour (solubility and leachability) was considered in order to highlight the presence of different chemical forms. In the period of interest (June 2015), daily averages PM concentrations were below the limit of 25?μg/m³ for PM_2.5 and 50?μg/m³for PM₁₀; moreover, for both fractions, the most abundant ionic species was SO₄^2?followed by NO₃^?. Ionic balance indicated that non-sea salt contribution accounted for the great part of Ca²⁺, SO₄^2? and K⁺ while secondary inorganic aerosol accounted for about 5% of total ionic fraction. As expected, the most abundant metal was zinc (about 41?ng/m³ and 44?ng/m³in PM_2.5 and PM_10, respectively), while cadmium, copper and lead were at very low concentrations, in the range of 0.01–0.47?ng/m³; leachability reached values of 40% for copper in both PM fractions, in contrast with zinc that showed the lowest leachability, corresponding to 6% for PM_2.5 fraction. The study on air masses trajectories indicated a change on ionic composition and chemical properties, varying from a condition with air masses coming from Eastern Europe, characterised also by higher concentrations of both PM_2.5 and PM₁₀, a prevalence of secondary aerosol and metals showing minor solubility and leachability, to a condition with air masses coming from North-west region, with characteristics opposed to the previous ones.

A recent paper reported GCxGC-TOFMS analysis used for the first time in southern Africa to tentatively characterise and semi-quantify ~1000 organic compounds in aerosols at Welgegund – a regional background atmospheric monitoring station. Ambient polar organic aerosols characterised are further explored in terms of temporal variations, as well as the influence of meteorology and sources. No distinct seasonal pattern was observed for the total number of polar organic compounds tentatively characterised and their corresponding semi-quantified concentrations (sum of the normalised response factors, ∑NRFs). However, the total number of polar organic compounds and ∑NRFs between late spring and early autumn seemed relatively lower compared to the period from mid-autumn to mid-winter, while there was a period during late winter and early spring with significantly lower total number of polar organic compounds and ∑NRFs. Relatively lower total number of polar organic compounds and corresponding ∑NRFs were associated with fresher plumes from a source region relatively close to Welgegund. Meteorological parameters indicated that wet removal during late spring to early autumn also contributed to lower total numbers of polar organics and associated ∑NRFs. Increased anticyclonic recirculation and more pronounced inversion layers contributed to higher total numbers of polar organic species and ∑NRFs from mid-autumn to mid-winter, while the influence of regional biomass burning during this period was also evident. The period with significantly lower total number of polar organic compounds and ∑NRFs was attributed to fresh open biomass burning plumes occurring within proximity of Welgegund, consisting mainly of volatile organic compounds and non-polar hydrocarbons. Multiple linear regression substantiated that the temporal variations in polar organic compounds were related to a combination of the factors investigated in this study.

This study presents a yearlong data set of 28 medium-chain functionalised carboxylic acids (C5 to C10) in atmospheric aerosol particles (PM₁₀) from a German rural measurement station, which is analysed to obtain seasonal trends and evidences for possible sources of these rarely studied compounds. The analysed carboxylic acids were divided into four main groups: (I) functionalised aliphatic monocarboxylic acids, (II) functionalised aromatic monocarboxylic acids, (III) non-functionalised and functionalised aliphatic dicarboxylic acids, and (IV) aromatic dicarboxylic acids. A concentration maximum in summer was observed for aliphatic carboxylic acids, indicating mainly photochemical formation processes. For example, the highest mean summer concentrations were observed for 4-oxopentanoic acid (4.1?ng?m^?3) in group I and for adipic acid (10.3?ng?m^?3) in group III. In contrast, a concentration maximum in winter occurred for aromatic carboxylic acids, hinting at anthropogenic sources like residential heating. The highest mean winter concentrations were observed for 4-hydroxybenzoic acid (2.4?ng?m^?3) in group II and for phthalic acid (5.8?ng?m^?3) in group IV. For the annual mean concentrations, highest values were found for adipic acid and 4-oxopimelic acids with 7.8?ng?m^?3 and 6.1?ng?m^?3, respectively. The concentrations of oxodicarboxylic acids exceeded those of their corresponding unsubstituted form. Accordingly, straight-chain dicarboxylic acids might act as precursor compounds for their respective oxygenated forms. Similarly, unsubstituted monocarboxylic acids are possible precursors for functionalised aliphatic monocarboxylic acids. The present study contributes to the speciation of organic content on a molecular level of atmospheric particles, as well as giving hints for possible sources for these carboxylic acids.