The chemical composition of ambient organic aerosols was analyzed using complementary mass spectrometric techniques during a field study in central Europe in July 2014 (Fichtelgebirge – Biogenic ...Emission and Aerosol Chemistry, F-BEACh 2014). Among several common biogenic secondary organic aerosol (BSOA) marker compounds, 93 acidic oxygenated hydrocarbons were detected with elevated abundances and were thus attributed to be characteristic for the organic aerosol mass at the site. Monoterpene measurements exhibited median mixing ratios of 1.6 and 0.8 ppbV for in and above canopy levels respectively. Nonetheless, concentrations for early-generation oxidation products were rather low, e.g., pinic acid (c = 4.7 (±2.5) ng m−3). In contrast, high concentrations were found for later-generation photooxidation products such as 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA, c = 13.8 (±9.0) ng m−3) and 3-carboxyheptanedioic acid (c = 10.2 (±6.6) ng m−3), suggesting that aged aerosol masses were present during the campaign period. In agreement, HYSPLIT trajectory calculations indicate that most of the arriving air masses traveled long distances (> 1500 km) over land with high solar radiation. In addition, around 47 % of the detected compounds from filter sample analysis contained sulfur, confirming a rather high anthropogenic impact on biogenic emissions and their oxidation processes. Among the sulfur-containing compounds, several organosulfates, nitrooxy organosulfates, and highly oxidized organosulfates (HOOS) were tentatively identified by high-resolution mass spectrometry. Correlations among HOOS, sulfate, and highly oxidized multifunctional organic compounds (HOMs) support the hypothesis of previous studies that HOOS are formed by reactions of gas-phase HOMs with particulate sulfate. Moreover, periods with high relative humidity indicate that aqueous-phase chemistry might play a major role in HOOS production. However, for dryer periods, coinciding signals for HOOS and gas-phase peroxyradicals (RO2 ) were observed, suggesting RO2 to be involved in HOOS formation.
The aerosol chemical speciation monitor (ACSM) is nowadays widely used to identify and quantify the main components of fine particles in ambient air. As such, its deployment at observatory platforms ...is fully incorporated within the European Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS). Regular intercomparisons are organized at the Aerosol Chemical Monitoring Calibration Center (ACMCC; part of the European Center for Aerosol Calibration, Paris, France) to ensure the consistency of the dataset, as well as instrumental performance and variability. However, in situ quality assurance remains a fundamental aspect of the instrument's stability. Here, we present and discuss the main outputs of long-term quality assurance efforts achieved for ACSM measurements at the research station Melpitz (Germany) since 2012 onwards. In order to validate the ACSM measurements over the years and to characterize seasonal variations, nitrate, sulfate, ammonium, organic, and particle mass concentrations were systematically compared against the collocated measurements of daily offline high-volume PM.sub.1 and PM.sub.2.5 filter samples and particle number size distribution (PNSD) measurements. Mass closure analysis was made by comparing the total particle mass (PM) concentration obtained by adding the mass concentration of equivalent black carbon (eBC) from the multi-angle absorption photometer (MAAP) to the ACSM chemical composition, to that of PM.sub.1 and PM.sub.2.5 during filter weighing, as well as to the derived mass concentration of PNSD. A combination of PM.sub.1 and PM.sub.2.5 filter samples helped identifying the critical importance of the upper size cutoff of the ACSM during such exercises. The ACSM-MAAP-derived mass concentrations systematically deviated from the PM.sub.1 mass when the mass concentration of the latter represented less than 60 % of PM.sub.2.5, which was linked to the transmission efficiency of the aerodynamic lenses of the ACSM. The best correlations are obtained for sulfate (slope =0.96; R.sup.2 =0.77) and total PM (slope =1.02; R.sup.2 =0.90). Although, sulfate did not exhibit a seasonal dependency, total PM mass concentration revealed a small seasonal variability linked to the increase in non-water-soluble fractions. The nitrate suffers from a loss of ammonium nitrate during filter collection, and the contribution of organo-nitrate compounds to the ACSM nitrate signal make it difficult to directly compare the two methods. The contribution of m/z 44 (f.sub.44) to the total organic mass concentration was used to convert the ACSM organic mass (OM) to organic carbon (OC) by using a similar approach as for the aerosol mass spectrometer (AMS). The resulting estimated OC.sub.ACSM was compared with the measured OCPM1 (slope =0.74; R.sup.2 =0.77), indicating that the f.sub.44 signal was relatively free of interferences during this period. The PM.sub.2.5 filter samples use for the ACSM data quality might suffer from a systematic bias due to a size truncation effect as well as to the presence of chemical species that cannot be detected by the ACSM in coarse mode (e.g., sodium nitrate and sodium sulfate). This may lead to a systematic underestimation of the ACSM particle mass concentration and/or a positive artifact that artificially decreases the discrepancies between the two methods. Consequently, ACSM data validation using PM.sub.2.5 filters has to be interpreted with extreme care. The particle mass closure with the PNSD was satisfying (slope =0.77; R.sup.2 =0.90 over the entire period), with a slight overestimation of the mobility particle size spectrometer (MPSS)-derived mass concentration in winter. This seasonal variability was related to a change on the PNSD and a larger contribution of the supermicrometer particles in winter.
DOI: 10.1002/jssc.201900689
The cover picture shows a schematic presentation of a new method to analyze imidazole compounds in ambientparticles. Aqueous particle extracts are prepared and ...subsequently analyzed by UHPLC‐Orbitrap‐MS. The extracted ion chromatogram shows the successful separation of the 10 model imidazoles with the final optimized method. Imidazoles found in ambient aerosol particles are indicated with their corresponding chemical structures.
Agro-industrial areas are frequently affected by various sources of atmospheric pollutants that have a negative impact on public health and ecosystems. However, air quality in these areas is ...infrequently monitored because of their smaller population compared to large cities, especially in developing countries. The Cauca River valley (CRV) is an agro-industrial region in southwestern Colombia, where a large fraction of the area is devoted to sugarcane and livestock production. The CRV is also affected by road traffic and industrial emissions. This study aims to elucidate the chemical composition of particulate matter fine mode (PM2.5) and to identify the main pollutant sources before source attribution. A sampling campaign was carried out at a representative site in the CRV region, where daily averaged mass concentrations of PM2.5 and the concentrations of water-soluble ions, trace metals, organic and elemental carbon, and various fractions of organic compounds (carbohydrates, n alkanes, and polycyclic aromatic hydrocarbons – PAHs) were measured. The mean PM2.5 was 14.4±4.4 µg m−3, and the most abundant constituent was organic material (52.7 % ± 18.4 %), followed by sulfate (12.7 % ± 2.8 %), and elemental carbon (7.1 % ± 2.5 %), which indicates the presence of secondary aerosol formation and incomplete combustion. Levoglucosan was present in all samples, with a mean concentration of (113.8±147.2 ng m−3), revealing biomass burning as a persistent source. Mass closure using the elemental carbon (EC) tracer method explained 88.4 % on PM2.5, whereas the organic tracer method explained 70.9 % of PM2.5. We attribute this difference to the lack of information of specific organic tracers for some sources, both primary and secondary. Organic material and inorganic ions were the dominant groups of species (79 % of PM2.5). OMprim and OMsec contribute 24.2 % and 28.5 % to PM2.5. Inorganic ions as sulfate, nitrate, and ammonia constitute 19.0 %, EC 7.1 %, dust 3.5%, particle-bounded water (PBW) 5.3 %, and trace element oxides (TEOs), 0.9 % of PM2.5. The aerosol was acidic, with a pH of 2.5±0.4, mainly because of the abundance of organic and sulfur compounds. Diagnostic ratios and tracer concentrations indicate that most PM2.5 was emitted locally and had contributions of both pyrogenic and petrogenic sources, that biomass burning was ubiquitous during the sampling period and was the main source of PAHs, and that the relatively low PM2.5 concentrations and mutagenic potentials are consistent with low-intensity, year-long biomass burning (BB) and sugarcane pre-harvest burning in the CRV.
Imidazoles are widely discussed in recent literature. They have been studied as a secondary product of the reaction of dicarbonyls with nitrogen containing compounds in a number of laboratory ...studies, potentially acting as photosensitizers triggering secondary organic aerosol growth and are forming constituents of light absorbing brown carbon. Despite the knowledge from laboratory studies, no quantitative information about imidazoles in ambient aerosol particles is available. Within the present study, five imidazoles (1-butylimidazole, 1-ethylimidazole, 2-ethylimidazole, imidazol-2-carboxaldehyde, and 4(5)-methylimidazole) were successfully identified and quantified for the first time in ambient aerosol samples from different environments in Europe and China. Their concentrations range between 0.2 and 14 ng/m3. 4(5)-Methylimidazole was found to be the most abundant imidazole. The occurrence of imidazoles seems to be favored at sites with strong biomass burning influence or connected to more polluted air masses. No connection was found between aerosol particle pH and imidazole concentration. Our work corroborates the laboratory studies by showing that imidazoles are present in ambient aerosol samples in measurable amounts. Moreover, it further motivates to explore the potential photosensitizing properties of small alkyl-substituted imidazoles.
Humic‐like substances (HULIS) constitute a significant fraction of aerosol particles in different environments. Studies of the role of HULIS in hygroscopic growth and cloud condensation nuclei (CCN) ...activity of aerosol particles are scarce, and results differ significantly. In this work the hygroscopic growth and CCN activity of water extracts (WE) and HULIS extracted from particulate matter (PM) collected at a polluted urban site (Copenhagen, Denmark), a rural site (Melpitz, Germany) and the remote site Storm Peak Laboratory (Colorado, USA) were investigated. Measurements of inorganic ions, elemental carbon, organic carbon and water soluble organic carbon (WSOC) within the PM confirmed that the sources of aerosol particles most likely differed for the three samples. The hygroscopic properties of the filtered WE were characterized by hygroscopicity parameters for subsaturated conditions (κGF) of 0.25, 0.41 and 0.22, and for supersaturated conditions κCCN were 0.23, 0.29 and 0.22 respectively for the urban, rural and remote WE samples. The measured hygroscopic growth and CCN activity were almost identical for the three HULIS samples and could be well represented by κGF = 0.07 and κCCN = 0.08–0.10 respectively. Small amounts of inorganic ions were present in the HULIS samples so the actual values for pure HULIS are expected to be slightly lower (κGF* = 0.04–0.06 and κCCN* = 0.07–0.08). The HULIS samples are thus less hygroscopic compared to most previous studies. To aid direct comparison of hygroscopic properties of HULIS from different studies, we recommend that the fraction of inorganic species in the HULIS samples always is measured and reported.
Key Points
The CCN activity of HULIS from different environments is similar
The hygroscopic growth of HULIS particles from different environments is similar
HULIS may in general be less hygroscopic than previous studies indicate
Global sulfate production plays a key role in aerosol radiative forcing; more than half of this production occurs in clouds. We found that sulfur dioxide oxidation catalyzed by natural transition ...metal ions is the dominant in-cloud oxidation pathway. The pathway was observed to occur primarily on coarse mineral dust, so the sulfate produced will have a short lifetime and little direct or indirect climatic effect. Taking this into account will lead to large changes in estimates of the magnitude and spatial distribution of aerosol forcing. Therefore, this oxidation pathway-which is currently included in only one of the 12 major global climate models-will have a significant impact on assessments of current and future climate.
Sub-micron marine aerosol particles (PM
1
) were collected over the period 22 June–21 July 2011 during the RV MARIA S. MERIAN cruise MSM 18/3, which travelled from the Cape Verdean island of São ...Vicente to Gabon, in the process crossing the tropical Atlantic Ocean with its equatorial upwelling regime. According to air mass origin and the chemical composition of the sampled aerosol particles, three main regimes could be established. Aerosol particles in the first part of the cruise were mainly of marine origin (
Region I
). In the second part of the cruise, marine influences mixed with increasing influence from biomass burning (
Region II
). In the final part of the cruise, which approached the African mainland, the biomass burning influence became dominant (
Region III
). Generally, aerosol particles were dominated by sulfate (c
average
= 2.0 μg m
−3
) and ammonium ions (c
average
= 0.7 μg m
−3
), which were well-correlated and increased slightly over the duration of the cruise. High concentrations of water-insoluble organic carbon (WISOC; c
average
= 0.4 μg m
−3
) were found, most likely as a result of the high oceanic productivity in this region. Water-soluble organic carbon (WSOC) concentrations increased from 0.26 μg m
−3
in
Region I
to 2.3 μg m
−3
in
Region III
, most likely as a result of biomass burning influences. The major organic aerosol constituents were oxalic acid, methanesulfonic acid (MSA), and aliphatic amines. MSA concentrations were quite constant during the cruise (c
average
= 42 ng m
−3
). Aliphatic amines were most abundant in
Region I
, with concentrations of ~ 20 ng m
−3
. Oxalic acid showed the opposite trend, with average concentrations of 12 ng m
−3
in
Region I
and 158 ng m
−3
in
Region III
. The α-dicarbonyl compounds glyoxal and methylglyoxal were detected in the aerosol particles in the low ng m
−3
range and were closely correlated with oxalic acid. MSA and aliphatic amines arise from biogenic marine sources, whereas oxalic acid and the α-dicarbonyl compounds were attributed to biomass burning. Concentrations of n-alkanes increased from 0.8 to 4.7 ng m
−3
over the duration of the cruise. PAHs and hopanes were abundant only in
Region III
(c
average
of PAHs = 0.13 ng m
−3
; c
average
of hopanes = 0.19 ng m
−3
). Levoglucosan was identified in several samples obtained in
Region III
, with c
average
= 1.9 ng m
−3
, which points to (aged) biomass burning influences. The organic compounds quantified in this study could explain 8.3 % of WSOC in
Regions I
, where aliphatic amines and MSA dominated, 3.7 % of WSOC in
Region II
and 2.5 % of WSOC in
Region III
, where oxalic acid dominated.
Aliphatic amines are important constituents of the marine environment. However, their biogenic origins, formation processes and roles in atmospheric chemistry are still not well understood. Here we ...present measurements of monomethylamine (MMA), dimethylamine (DMA) and diethylamine (DEA) from two intensive sampling campaigns at the Cape Verde Atmospheric Observatory (CVAO), a remote marine station in the tropical Atlantic Ocean. The amines were measured in the sea surface microlayer (SML), in bulk seawater, in the gas and the submicron particulate aerosol phase. Additionally, a 24-month record of amine concentrations in aerosol particles, together with other particle constituents and biological and meteorological parameters, is presented. In the SML, mean amine concentrations were in the range 20–50 nmol L−1. The correlation of the amines to chlorophyll-a (R2 = 0.52) and the abundance of the diatom pigment fucoxanthin may indicate that amines were formed via algal production. Amine concentrations in the gas and particulate aerosol phases were dominated by DMA, with average concentrations of 4.5 ng m−3 and 5.6 ng m−3, respectively. Average MMA concentrations were 0.8 ng m−3 in the gas phase and 0.2 ng m−3 in the particle phase. DEA was present in the particle phase with an average concentration of 3.9 ng m−3, but was not detected in the gas phase. Sea to air fluxes for MMA and DMA were calculated from the seawater and gaseous amine concentrations; these varied from −8.7 E−14 to +4.0 E−13 mol m−2 s−1 and from −1.9 E−12 to +2.17 E−12 mol m−2 s−1, respectively. While the flux for MMA was mainly positive, suggesting an oceanic source for this analyte, the flux for DMA could be both positive and negative, indicating that 2-way transport may be occurring. Principal component analysis of the 24-month dataset of amines in aerosol particles revealed that the particulate amines were not directly linked to the identified sources. It seems that the transfer of amines was being determined by gas to particle conversion rather than via primary processes. The correlation of both seawater- and gas phase-amines with biological indicators suggests that they were partly linked and that the amine abundance in the atmosphere (gas phase) reflected biological processes in seawater. In contrast, particulate amine concentrations did not show such a direct response and might have other significant sources and environmental drivers.
Display omitted
•Aliphatic amines are present in the tropical remote Atlantic Ocean and Atmosphere.•Amines in the seawater and gas phase are connected to biological activity.•Ocean can be a sink or a source of amines.•Sources of amines in the submicron particle phase are probably not of primary nature.
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