High-resolution Time-of-flight Aerosol Mass Spectrometer Research Articles

Measurements of particulate methanesulfonic acid above the remote Arctic Ocean using a high resolution aerosol mass spectrometer

Methanesulfonic acid (MSA) is an important product from the oxidation of dimethyl sulfide (DMS), and thus is often used as a tracer for marine biogenic sources and secondary organic aerosol. MSA also contributes to aerosol mass and potentially to the formation of cloud condensation nuclei and new particles. However, measurements of MSA at high temporal resolution in the remote Arctic are scarce, which limits our understanding of its formation, climate change impact and regional transport. Here, we applied a validated quantification method to determine the mass concentration of MSA and non-sea salt sulfate (nss-SO4) in PM2.5 in the marine boundary layer, using a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) during a research cruise to the Arctic and North Atlantic Ocean, between 55 °N and 68 °N (26th May to June 23, 2022). With this method, the concentrations of MSA in the remote Arctic marine boundary layer were determined for the first time. Results show that the average MSA concentration was 0.025 ± 0.03 μg m−3, ranging from <0.01 to 0.32 μg m−3. The lowest MSA level was found towards the northern leg of the cruise (near Sisimut (67 °N)) with air masses from sea ice over the northern polar region, and the highest MSA concentrations were observed over the Atlantic open ocean. The diurnal cycles of gas MSA, particulate MSA and nss-SO4 peaked in the afternoon, about one hour later than that of peak of solar radiation, which suggests that photochemical process is an important mechanism for the conversion of DMS into MSA above the remote ocean. The mass ratio of MSA to nss-SO4 (MSA/nss-SO4) presents a temperature dependence, which indicates that the addition branching pathway favors MSA formation, while thermal decay of intermediate radicals could be a possible pathway for sulfate formation. Finally, we found that the MSA/nss-SO4 ratio is around 0.22-0.25 in the remote northern marine atmosphere.

Comprehensive the seasonal characterization of atmospheric submicron particles at urban sites in the North China Plain

To comprehensively investigate the seasonal variations in submicron particles (PM1 = NR-PM1 + BC) composition, sources and chemical processes, an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), along with a multiangle absorption photometer (MAAP), was deployed to observe at urban sites in the North China Plain from October 1, 2015, to July 31, 2016. The PM1 average mass were 36.4 ± 39.0, 32.9 ± 20.7, 40.4 ± 52.4 and 99.0 ± 88.7 μg m−3 in spring, summer, autumn and winter, respectively. On the whole, the OA accounted for the largest component of PM1 during the four seasons, with the highest contribution in winter, accounting for 49% on average, followed by autumn (47%), spring (40%) and summer (31%). The secondary inorganic aerosol (SIA) mass concentration in summer was the lowest but contributed the most to PM1 in summer (62%), and it was higher than that in spring (46%), autumn (43%) and winter (41%). Positive matrix factorization (PMF) was used to differentiate the high-resolution mass spectra (HRMS) of organic aerosol (OA) into six factors, including two secondary OA (highly oxidized, low-volatility oxygenated organic aerosols (LV-OOA) and less oxidized, semi-volatile oxygenated OA (SV-OOA)) and four primary OA (including cooking-related OA (COA), hydrocarbon-like OA (HOA), biomass burning OA (BBOA) and coal combustion OA (CCOA)). OOA (LV-OOA + SV-OOA) exhibited the highest OA loading in summer (59%), while POA (CCOA + COA + HOA) exhibited the highest OA loading in winter (62%). The OA exhibited similar bimodal diurnal patterns during the four seasons, the nitrate and sulfate seasonal diurnal variations slightly differed, and the peak value occurred at night in winter and in the morning during the other seasons. The trend of the LV-OOA and SV-OOA diurnal variation in spring, autumn and winter appeared small difference, and the summer vary differently compared to other seasons. However, the diurnal mass concentration in winter was much higher than other seasons. The COA diurnal pattern peaked at noon and at night during the four seasons, corresponding to the peak hours of dining activities. The HOA, BBOA and CCOA seasonal diurnal patterns showed low concentrations during the daytime and high concentrations at night. OA on HPD was 6, 7 and 7 times higher than that on CD in spring, autumn and winter. The SIA concentration significantly increased on HPD in spring (69.3 μg m−3, 52%), autumn (80.6 μg m−3, 50%) and winter (82.4 μg m−3, 43%). The organic nitrate average mass concentrations were 0.6 ± 0.5, 0.7 ± 0.2, 0.8 ± 1.2 and 2.5 ± 2.3 μg m−3 in spring, summer, autumn and winter, respectively. The organic nitrate diurnal pattern appeared at night was higher than that during the daytime in spring, autumn and winter. The opposite diurnal pattern emerged in summer. The average mass concentration of polycyclic aromatic hydrocarbons (PAHs) during the entire observation period reached 73.2 ± 154.2 ng m−3, and the seasonal average mass were 30.4 ± 30.6, 10.7 ± 4.0, 40.5 ± 10.3 and 220.3 ± 246.7 ng m−3 in spring, summer, autumn and winter, respectively. The highest diurnal values in spring, summer, autumn and winter were 44.2, 11.7, 71.6 and 366.8 ng m−3, respectively.

Quantifying the Chemical Composition and Real-Time Mass Loading of Nanoplastic Particles in the Atmosphere Using Aerosol Mass Spectrometry.

Plastic debris, including nanoplastic particles (NPPs), has emerged as an important global environmental issue due to its detrimental effects on human health, ecosystems, and climate. Atmospheric processes play an important role in the transportation and fate of plastic particles in the environment. In this study, a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was employed to establish the first online approach for identification and quantification of airborne submicrometer polystyrene (PS) NPPs from laboratory-generated and ambient aerosols. The fragmentation ion C8H8+ is identified as the major tracer ion for PS nanoplastic particles, achieving an 1-h detection limit of 4.96 ng/m3. Ambient PS NPPs measured at an urban location in Texas are quantified to be 30 ± 20 ng/m3 by applying the AMS data with a constrained positive matrix factorization (PMF) method using the multilinear engine (ME-2). Careful analysis of ambient data reveals that atmospheric PS NPPs were enhanced as air mass passed through a waste incinerator plant, suggesting that incineration of waste may serve as a source of ambient NPPs. The online quantification of NPPs achieved through this study can significantly improve our understanding of the source, transport, fate, and climate effects of atmospheric NPPs to mitigate this emerging global environmental issue.

Differences in Secondary Organic Aerosol Formation from α-Pinene Photooxidation in a Chamber with Purified Air and Ambient Air as Matrices: Preliminary Results

α-Pinene is a biogenic volatile organic compound (BVOC) that significantly contributes to secondary organic aerosols (SOA) in the atmosphere due to its high emission rate, reactivity, and SOA yield. However, the SOA yield measured in chamber studies from α-pinene photooxidation is limited in a purified air matrix. Assessing SOA formation from α-pinene photooxidation in real urban ambient air based on studies conducted in purified air matrices may be subject to uncertainties. In this study, α-pinene photooxidation and SOA yield were investigated in a smog chamber in the presence of NO and SO2 under purified air and ambient air matrices. With the accumulation of ozone (O3) during the photooxidation, an increasing part of α-pinene was consumed by O3 and finally nearly half of the α-pinene was oxidized by O3, facilitating the production of highly oxidized organic molecules and thereby SOA formation. Although the ambient air we introduced as matrix air was largely clean, with initial organic aerosol mass concentrations of ~1.5 μg m−3, the α-pinene SOA yield in the ambient air matrix was 42.3 ± 5.3%, still higher than that of 32.4 ± 0.4% in the purified air matrix. The chemical characterization of SOA by the high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) revealed that CxHy accounted for 53.7 ± 1.1% of the total signal in the ambient air matrix experiments, higher than 48.1 ± 0.3% in the purified air, while CxHyO and CxHyO&gt;1 together constituted 45.0 ± 0.9% in the ambient air matrix, lower than 50.1 ± 1.0% in the purified air. The O:C ratio in the ambient air matrix experiments was 0.41 ± 0.01, lower than 0.46 ± 0.01 in the purified air. The higher SOA yield of α-pinene in the ambient air matrix compared to that in the purified air matrix was partly due to the presence of initial aerosols in the ambient air, which facilitated the low volatile organic compounds produced from photochemical oxidation to enter the aerosol phase through gas-particle partitioning. The in-situ aerosol acidity calculated by the ISORROPIA-II model in the ambient air matrix experiments was approximately six times higher than that in purified air, and the higher SOA yield in the ambient air matrix experiments might also be attributed to acid-catalyzed SOA formation.

Airmass history, night-time particulate organonitrates, and meteorology impact urban SOA formation rate

With respect to air quality, the San Antonio metropolitan area, with a population of 1.45 million and the second largest city in Texas, has been designated as non-attainment by the United States Environmental Protection Agency in recent years. Despite the operation of multiple stationary air quality monitoring sites by the Texas Commission on Environmental Quality, the in-situ measurements of submicron aerosol and its precursors in the region is limited. To better understand the formation of secondary organic aerosol (SOA) in the San Antonio urban core, we conducted observations of a range of trace gases, volatile organic compounds, submicron aerosol, and meteorological parameters in May 2017. Data from a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) show that organic aerosol (OA) was the dominant component of non-refractory submicron particulate matter (average±1σ, 55 ± 32 %, 5.86 ± 3.40 μg m−3), followed by sulfate (33 ± 23 %, 3.52 ± 2.47 μg m−3). Aerosol liquid water contents predicted by ISORROPIA-II greatly increase from Continental to Oceanic airmass history scenarios, while inorganic aerosol pH remains very acidic. Positive matrix factorization (PMF) analysis of the OA mass spectra indicates that two classes of oxygenated OA (less and more-oxidized OOA, LO and MO) together constituted the bulk of OA mass during the study period (MO-OOA: 44 ± 39 %, 2.35 ± 2.07 μg m−3; LO-OOA: 42 ± 34 %, 2.22 ± 1.77 μg m−3), while the fraction of hydrocarbon-like OA was limited (13 ± 21 %, 0.71 ± 1.11 μg m−3). Using in-situ meteorological data and location-specific empirical coefficients, a zero-dimensional model that utilized PMF factors as proxies to calculate the net rate of formation of types of SOA has been developed; similar calculations were used to estimate the formation rate of particulate organonitrates (pON). The results from the model reveal the importance of pON formation in LO-OOA formation overnight and the influence of temperature and photochemistry during the day. The relationships between local atmospheric factors and the net rate of formation of MO-OOA are not statistically significant. These results emphasize how HR-ToF-AMS-PMF factors could be incorporated into chemistry modeling to evaluate quantitatively the rates of formation of SOA and reveal diurnal differences in SOA formation pathways in a major urban area in southern United States.

Evaluation of aerosol- and gas-phase tracers for identification of transported biomass burning emissions in an industrially influenced location in Texas, USA

Abstract. As criteria pollutants from anthropogenic emissions have declined in the US in the last 2 decades, biomass burning (BB) emissions are becoming more important for urban air quality. Tracking the transported BB emissions and their impacts is challenging, especially in areas that are also burdened by anthropogenic sources like the Texas Gulf Coast. During the Corpus Christi and San Antonio (CCSA) field campaign in spring 2021, two long-range-transport BB events (BB1 and BB2) were identified. The observed patterns of an absorption Ångström exponent (AAE), a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) BB tracer (f60), equivalent black carbon (eBC), acetonitrile and carbon monoxide (CO) during BB1 and BB2 indicated differences in the mixing of transported BB plumes with local anthropogenic sources. The combined information from HYSPLIT backward-trajectory (BT) and satellite observations revealed that BB1 had mixed influence of transported smoke plumes from fires in central Mexico, the Yucatán Peninsula and the central US, whereas BB2 was influenced by fires in the central US. The estimated transport times of smoke from the Mexican fires and the central US fires to our study site were not too different (48–54 and 24–36 h, respectively), and both events appeared to have undergone similar levels of atmospheric processing, as evident in the elemental ratios of bulk organic aerosol (OA). We observed an aging trend for f44 vs. f60 and f44 vs. f43 as a function of time during BB2 but not during BB1. Positive matrix factorization (PMF) analysis of OA showed that BB1 had a mixture of organics from aged BB emissions with an anthropogenic marine signal, while the oxidized organic compounds from aged BB emissions dominated the aerosols during BB2. The size distribution of aerosol composition revealed distinct characteristics between BB1 and BB2, where BB1 was found to be externally mixed, exhibiting a combination of BB and anthropogenic marine aerosols. On the other hand, BB2 exhibited internal mixing dominated by aged BB aerosol. Our analysis from mobile and stationary measurements highlights that both CO and acetonitrile are likely impacted by local sources even during the BB events and specifically that acetonitrile cannot be used as a unique BB tracer for dilute BB plumes in an industrially influenced location. A suitable volatile organic compound (VOC) tracer would need to be emitted in high concentrations during BB, resistant to degradation during transport, unique to BB and able to be measured in the field. This study effectively demonstrates that AAE and aerosol BB tracers served as precise and effective tracers in these complex emission scenarios. Network deployment of multiwavelength photometers holds promise for enhancing our understanding of BB impacts on air quality and supporting informed decision-making for effective mitigation strategies in locations with mixed sources and influence of dilute BB plumes. To demonstrate the relevance of such an aerosol optical network, we provide evidence of the potential regional impacts of these transported BB events on urban O3 levels using measurements from the surface air quality monitoring network in Texas.

Characteristics of Seasonal PM1 Chemical Components in the urban area of Ansan

In this study, chemical properties of particulate matter (PM&lt;sub&gt;1&lt;/sub&gt;) present in the urban area of Ansan in 2021 were analyzed using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Intensive observation was conducted during the measurement periods of spring (22 days), summer (29 days), autumn (60 days), and winter (29 days). High concentrations of PM&lt;sub&gt;1&lt;/sub&gt; were observed when a wind speed was low (&lt; 0.81 m/s) and a direction of air flow was the east. PM&lt;sub&gt;1&lt;/sub&gt; concentration was the highest in spring (March), followed by summer (June and August), winter (December), and autumn (September and October). The main components of PM&lt;sub&gt;1&lt;/sub&gt; were organic, followed by nitrate, ammonium, and sulfate. The ratio of organic oxygen to organic carbon (O/C) was high in summer (0.64) and low in winter (0.51); conversely, the ratio of organic hydrogen to organic carbon (H/C) was higher in winter (1.66) than in summer (1.58). As for the oxidation rates of inorganic components, the nitrogen oxidation rate and sulfur oxidation rate were the highest in spring (NOR, 0.12; SOR, 0.64), which directly affected the rise in PM&lt;sub&gt;1&lt;/sub&gt; mass concentration in spring. Highly soluble nitrate was the largest component among the inorganic components of PM&lt;sub&gt;1&lt;/sub&gt;, and the PM&lt;sub&gt;1&lt;/sub&gt; was found to be rich in ammonium in all seasons. PM&lt;sub&gt;1&lt;/sub&gt; mass concentration and chemical composition increased with an increase of relative humidity (RH): the concentration of PM&lt;sub&gt;1&lt;/sub&gt; in wet conditions (RH &gt; 60%) was found to be more than twice of that in dry conditions (RH &lt; 40%). The largest component of PM&lt;sub&gt;1&lt;/sub&gt; in Ansan consisted of organic compounds; however, a high proportion of inorganic components, including nitrate, was also recorded.

Deposition of secondary organic aerosol in human lung model: Effect of photochemically aged aerosol on human respiratory system

Ultrafine particles (UFP) of Secondary Organic Aerosol (SOA) penetrate deep into the human respiratory system and exert fatal effects on human health. However, there is little data on the potential deposited doses of UFP-generated SOA in the human respiratory tract. This study is to estimate the fraction of aerosol deposition using a multiple-path-particle-dosimetry (MPPD) model. For relevancy of real life, the model employed measured concentrations of toluene-derived fresh and aged SOA produced within serially connected smog chamber and PAM-OFR (Potential Aerosol Mass-Oxidation Flow Reactor) under atmospheric environmental conditions (NOx and relative humidity). The number concentrations and chemical composition of fresh and aged aerosols produced within the chambers were measured using Scanning Mobility Particle Sizer (SMPS) and High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS), while the morphology of individual particles was analyzed using Scanning Electron Microscopy (SEM). The number concentration of aged SOA-w/s was more than double compared to that of fresh SOA-w/s (maximum reached after 10 h) with its size less than 100 nm. The O:C ratio for aged SOA-w/s were 0.96 and 1.15 depending on RH (0.96 at 3% RH and 1.15 at 50% RH), and individual spherical particles containing water were present in agglomerates with its size of less than 1 µm. In all inhalable fresh and aged SOA produced in the two chambers, 5–22% of aerosol is deposited in the Head airways, 4–8% in the tracheobronchial, and 8–34% in the alveolar regions. The predominant deposition of the aged aerosol occurred in the alveoli (in the generation 20th lobe), and the deposition faction in the alveoli was 2–3 times higher in the children group than the adults group. This study presented a quantitative exposure assessment of SOA generated under a realistic simulation and suggested the possibility of evaluating long-term exposure to SOA and potential health effects by determining the potential inhalable aerosol doses and the fraction of deposition in the human respiratory system.

Emissions from ships’ activities in the anchorage zone: A potential source of sub-micron aerosols in port areas

Busan Port is among the world’s top ten most air-polluted ports, but the role of the anchorage zone as a significant contributor to pollution has not been studied. To assess the emission characteristics of sub-micron aerosols, a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed in Busan, South Korea from September 10 to October 6, 2020. The concentration of all AMS-identified species and black carbon were highest when the winds came from the anchorage zone (11.9 µg·m−3) and lowest with winds from the open ocean (6.64 µg·m−3). The positive matrix factorization model identified one hydrocarbon-like organic aerosol (HOA) and two oxygenated organic aerosol (OOA) sources. HOAs were highest with winds from Busan Port, while oxidized OOAs were predominant with winds from the anchorage zone (less oxidized) and the open ocean (more oxidized). We calculated the emissions from the anchorage zone using ship activity data and compared them to the total emissions from Busan Port. Our results suggest that emissions from ship activities in the anchorage zone should be considered a significant source of pollution in the Busan Port area, especially given the substantial contributions of gaseous emissions (NOx: 8.78%; volatile organic compounds: 7.52%) and their oxidized moieties as secondary aerosols.

Influences of meteorology on emission sources and physicochemical properties of particulate matter in Seoul, Korea during the heating period

Chemical properties of particulate matter (PM), organic aerosol (OA) properties, sources and the volatility distribution were investigated during autumn in Seoul, Korea using aerodyne high resolution time of flight aerosol mass spectrometer (HR-ToF-AMS) with a thermodenuder (TD) combined system (TD-AMS). Overall, the average PM1 + black carbon (BC) concentration was 21.49 μg/m3, ranging from 7.85 μg/m3 to 48.36 μg/m3, and the largest proportion of PM1 components was organic (54%), followed by NO3− (17%), SO42− (12%), NH4+ (9%) and BC (6%). During this period, the O/C and H/C ratios were similar to those in other studies (0.45 and 1.70, respectively), but the N/C ratio was slightly higher than that in other studies. Five organic aerosol (OA) sources were identified through positive matrix factorization (PMF) analysis, where four POAs (HOA, COA, SFOA1 and SFOA2) and one SOA (LVOOA) were identified. A distinct feature during this study was that two different combustion-related sources, SFOA1 and SFOA2 were observed. Two different SFOAs showed time-dependent features and different chemical compositions. SFOA2, which was dominant during the higher-temperature period (16.3 °C (5.1–26.6)) showed less O/C (0.41 vs 0.57) and N/C (0.033 vs 0.059) and more volatile feature than the one of SFOA1 during colder period (10.1 °C (−1.8-19.4)). It might be due to different heating activities and more intensive gas to particle parting and oxidizing processing under colder condition. Haze is also influenced by heating activities. When stagnant conditions occur with high heating activities, enhanced emission sources (SFOA1), enhanced gas-to-particle partitioning (nitrate) and the accumulation of primary OA result in severe haze conditions in urban air. This result suggests that controlling emission sources during heating seasons is still required for haze control in urban environments.

Impact of aging on the sources, volatility, and viscosity of organic aerosols in Chinese outflows

Abstract. To investigate the impact of aging on the sources, volatility, and viscosity of organic aerosol (OA) in Chinese outflows, a high-resolution time-of-flight aerosol mass spectrometer (HR-AMS) coupled with a thermodenuder (TD) was deployed in the spring of 2018 in Dongying, which is a regional receptor site of metropolitan emissions in the North China Plain (NCP). The average mass concentration of PM1 is 31.5±22.7 µg m−3, which is mainly composed of nitrate (33 %) and OA (25 %). The source apportionment results show that the OA is mainly contributed by oxygenated OA (OOA) from secondary sources, including background-OOA (33 %) representing a background concentration of OA (2.6 µg m−3) in the NCP area, and transported-OOA (33 %) oxidized from urban emissions. The other two factors include aged hydrocarbon-liked OA (aged-HOA, 28 %) from transported vehicle emissions and biomass burning OA (BBOA, 5 %) from local open burning. The volatility of total OA (average C*=3.2×10-4 µg m−3) in this study is generally lower than that reported in previous field studies, which is mainly due to the high OA oxidation level resulting from aging processes during transport. The volatilities of OA factors follow the order of background-OOA (average C*=2.7×10-5 µg m−3) &lt; transported-OOA (3.7×10-4µgm-3)&lt; aged-HOA (8.1×10-4µgm-3)&lt; BBOA (0.012 µg m−3). Extremely low volatilities in ambient air indicate that oligomers may exist in aged plumes. The viscosity estimation suggests that the majority of ambient OA in this study behaves as semisolid (60 %), liquifies at higher relative humidity (RH) (21 %), and solidifies (19 %) during noon when the RH is low and the oxidation level is high. Finally, the estimated mixing time of molecules in 200 nm OA varies dramatically from minutes at night to years in the afternoon, emphasizing the need to consider its dynamic kinetic limits when modeling OA. In general, the overall results of this study improve our understanding of the impact of aging on OA volatility and viscosity.

Secondary organic aerosol formation in China from urban-lifestyle sources: Vehicle exhaust and cooking emission.

An increasing number of people tend to live in cities, where they suffer from serious air pollution from anthropogenic sources. Vehicle exhaust and cooking emission are closely related to daily life of urban residents, and could be defined as "urban-lifestyle sources". The primary emissions of urban-lifestyle sources tend to form abundant secondary organic aerosols (SOA) through complicated atmospheric chemistry processes. The newly formed SOA is a kind of complex mixture and causes considerable health effects with high uncertainty. Most studies focus on formation pathway, mass growth potential and chemical feature of urban-lifestyle SOA under simple laboratory conditions. Few studies have measured the urban-lifestyle SOA in ambient air, let alone verified laboratory findings under complicated atmospheric conditions. In this work, we established a new method that combined laboratory simulation and field observation, which quantified the urban-lifestyle SOA with high time resolution under the real atmospheric condition. The complex SOA was measured and resolved by a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The multilinear engine model (ME-2) and multilinear correction methods were used to apply laboratory results into ambient SOA apportionment. It was found that the vehicle source dominated the SOA formation during the diurnal photochemical process, and the SOA:POA ratio of vehicle source was about 1.4 times larger than that of cooking source. The vehicle emission may undergo an alcohol/peroxide & carboxylic acid oxidation pathway and form higher oxidized SOA, while the cooking emission may undergo an alcohol/peroxide oxidation pathway and form relatively lower oxidized SOA. The vehicle SOA and cooking SOA contributed 45.6 % and 24.8 % of OA during a local episode in 2021 winter of downtown Beijing. Our findings could not only provide a new way to quantify urban SOA but also demonstrate some laboratory hypotheses, conducing to understand its ambient contributions, chemical features, and environmental effects.

Seasonal Variation of Aerosol Composition and Sources of Water-Soluble Organic Carbon in an Eastern City of China

The mitigation of aerosol pollution is a great challenge in many cities in China, due to the complex sources and formation mechanism of particulate matter (PM) in different seasons. To understand the particular features of pollution in China and formulate different targeted policies, aerosol samples of PM2.5 were collected from January to October of 2018 in Longyou. The temporal profile of the meteorological parameters and the concentrations of water-soluble inorganic ions (WSIs) and organic matter (OM) were characterized. An Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-TOF-AMS) was also applied to further analyze the composition of water-soluble organic carbon (WSOC). The sources of WSOC were resolved by positive matrix factorization (PMF) analysis. The origin of air parcels and potential sources of WSOC were analyzed using a backward trajectory and potential source contribution function (PSCF). Winds from the northeast dominated each sampling period, and the relative humidity did not show a significant difference. The results showed that the proportion of OM in PM2.5 was the highest in summer and decreased in spring, autumn, and winter in turn. Four organic aerosol (OA) factors, including a hydrocarbon-like factor, a coal combustion factor, and two oxygenated OA factors, were identified in the WSOC by means of PMF analysis. The hydrocarbon-like OA (HOA) contributed the majority of the WSOC in summer, while the contribution of the coal-combustion OA (CCOA) increased significantly in winter, suggesting the presence of different sources of WSOC in different seasons. The air parcels from the north of China and Zhejiang province contributed to the CCOA in winter, while those from the marine regions in the south and southeast of China mainly contributed to the HOA during spring and summer. The weighted PSCF (WPSCF) analysis showed that the regions of east Zhejiang province were the main contributors, which means that local and regional emissions were the most probable source areas of WSOC. It implied that not only were the emissions control of both local and regional emissions important but also that the transport of pollutants needed to be sufficiently well accounted for to ensure the successful implementation of air pollution mitigation in Longyou.

Chemical characterization of sub-micron aerosols over the East Sea (Sea of Japan)

Studies of the land-sea-air interactions of aerosol are scarce considering their significant role in global environmental changes. Here, we investigated potential sources of sub-micron aerosols over the East Sea (Sea of Japan), which is strongly influenced by continental and marine aerosols. A high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was used to measure the size-resolved chemical compositions of sub-micron aerosols during the period March 10–15, 2020. Concentrations of all AMS species, black carbon (BC), PM10 (particulate matter <10 μm) and PM2.5 (particulate matter <2.5 μm) were higher when cruising in industrialized coastal areas compared to the offshore region. A positive matrix factorization (PMF) model identified five distinct sources, i.e., hydrocarbon-like organic aerosol, semi-volatile and low-volatile oxygenated aerosols, methanesulfonic acid (MSA), and dimethyl sulfide (DMS; C2H6S) oxidation, which accounted for 5.98 %, 21.6 %, 28.3 %, 34.5 %, and 9.64 % of the total organic mass, respectively. The spatiotemporal variation of MSA, as well as the MSA to sulfate ratio (MSA:SO42−) over the East Sea, was determined for the first time. The mass concentrations of MSA displayed a similar time series distribution pattern to those of DMS. The time series distributions of the MSA:SO42− ratio displayed distinct differences, with higher ratios downwind of the ocean (0.216 ± 0.083 μg·m−3) than land (0.089 ± 0.030 μg·m−3). The growth of ultrafine particles (10–35 nm) was observed during two of the elevated MSA:SO42− ratio events, suggesting a potential role of MSA in new particle formation.

Light absorption potential of water-soluble organic aerosols in the two polluted urban locations in the central Indo-Gangetic Plain

PM2.5 (particulate matter having aerodynamic diameter ≤2.5 μm) samples were collected during wintertime from two polluted urban sites (Allahabad and Kanpur) in the central Indo-Gangetic Plain (IGP) to comprehend the sources and atmospheric transformations of light-absorbing water-soluble organic aerosol (WSOA). The aqueous extract of each filter was atomized and analyzed in a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Water-soluble organic carbon (WSOC) and WSOA concentrations at Kanpur were ∼1.2 and ∼1.5 times higher than that at Allahabad. The fractions of WSOC and secondary organic carbon (SOC) to total organic carbon (OC) were also significantly higher ∼53% and 38%, respectively at Kanpur compared to Allahabad. This indicates a higher abundance of oxidized WSOA at Kanpur. The absorption coefficient (babs-365) of light-absorbing WSOA measured at 365 nm was 46.5 ± 15.5 Mm−1 and 73.2 ± 21.6 Mm−1 in Allahabad and Kanpur, respectively, indicating the dominance of more light-absorbing fractions in WSOC at Kanpur. The absorption properties such as mass absorption efficiency (MAE365) and imaginary component of refractive index (kabs-365) at 365 nm at Kanpur were also comparatively higher than Allahabad. The absorption forcing efficiency (Abs SFE; indicates warming effect) of WSOA at Kanpur was ∼1.4 times higher than Allahabad. Enhancement in light absorption capacity was observed with the increase in f44/f43 (fraction of m/z 44 (f44) to 43 (f43) in organic mass spectra) and O/C (oxygen to carbon) ratio of WSOA at Kanpur while no such trend was observed for the Allahabad site. Moreover, the correlation between carbon fractions and light absorption properties suggested the influence of low-volatile organic compounds (OC3 + OC4 fraction obtained from thermal/optical carbon analyzer) in increasing the light absorption capacity of WSOA in Kanpur.

Substantial organic impurities at the surface of synthetic ammonium sulfate particles

Abstract. Ammonium sulfate (AS) particles are widely used for studying the physical–chemistry processes of aerosols and for instrument calibrations. Small quantities of organic matter can greatly influence the studied properties, as observed by many laboratory studies. In this work, monodisperse particles (200–500 nm aerodynamic diameter) were generated by nebulizing various AS solutions and organic impurities were quantified relative to sulfate using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The organic content found in AS solutions was also tentatively identified using a liquid chromatography–tandem mass spectrometer (LC–MS). The results from both analytical techniques were consistent and demonstrated that the organic impurities contained oxygen, nitrogen, and/or sulfur, their molecular masses ranged from m/z 69 to 420, and they likely originate from the commercial AS crystals. For AS particle sizes ranging from 200 to 500 nm, the total mass fraction of organic compounds (relative to sulfate) ranged from 3.8 % to 1.5 %, respectively. An inorganic–organic mixture model suggested that the organic impurities were coated on the AS particle with a surface density of 1.1 × 10−3 g m−2. A series of tests were performed to remove the organic content (using pure N2 in the flow, ultrapure water in the solutions, and very high AS quality), showing that at least 40 % of the organic impurities could be removed. In conclusion, it is recommended to use AS seeds with caution, especially when small particles are used, in terms of AS purity and water purity when aqueous solutions are used for atomization.

Effect of NOx and RH on the secondary organic aerosol formation from toluene photooxidation

The secondary organic aerosol (SOA) formation mechanism and physicochemical properties can highly be influenced by relative humidity (RH) and NOx concentration. In this study, we performed a laboratory investigation of the SOA formation from toluene/OH photooxidation system in the presence or absence of NOx in dry and wet conditions. The chemical composition of toluene-derived SOA was measured using Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). It was found that the mass concentration of toluene decreased with increasing RH and NOx concentration. However, the change of SOA chemistry composition (f44, O/C) with increased RH was not consistent in the condition with or without NOx. The light absorption and mass absorption coefficient (MAC) of the toluene-derived SOA only increased with RH in the presence of NOx. In contrast, MAC is invariant with RH in the absence of NOx. HR-ToF-AMS results showed that, in the presence of NOx, the increased nitro-aromatic compounds and N/C ratio concurrently caused the increase of SOA light absorption and O/C in wet conditions, respectively. The relative intensity of CHON and CHOxN family to the total nitrogen-containing organic compounds (NOCs) increased with the increasing RH, and be the major components of NOCs in wet condition. This work revealed a synergy effect of NOx and RH on SOA formation from toluene photooxidation.

Variation Characteristics and Potential Sources of the Mt. Haituo Aerosol Chemical Composition in Different Pollution Processes During Winter in Beijing, China

In order to investigate the chemical composition and source apportionment of aerosols during winter in the Beijing-Tianjin-Heibei region, the particular matter (PM) and aerosol chemical composition at Mt. Haituo were observed by using a GRIMM 180, a single-particle soot photometer (SP2), and a high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS) from December 28, 2020 to February 3, 2021. Combining these observations with meteorological data and the HYSPLIT model, we calculated the potential source contribution factor (PSCF) and concentration weighted trajectory (CWT) and analyzed the temporal evolution and potential sources apportionment of PM and aerosol chemical composition under different pollution processes. The results showed that the dust storm process mainly affected PM10 and PM2.5 in Mt. Haituo during the winter and had a small impact on PM1; by contrast, haze pollution mainly affected PM1. Chemical components of aerosol accounted for 85.0% and 73.4% of PM1 on clean and haze days, respectively, but only 47.4% of PM1 in dust storm processes. NO3- was the chemical component with the largest mass concentration in haze, accounting for 25.2% of PM1; black carbon (BC) had the largest mass concentration on clean and dust storm days, accounting for 24.1% and 12.8% of PM1, respectively. The median diameters of BC were 209.7, 207.5, and 204.7 nm on clean, dust storm, and haze days, respectively. Dp/Dc was 2.15 in haze pollution, which was 1.38 and 1.39 times that on dust storm and clean days, respectively. Diurnal variations in PM and aerosol chemical components were different during the different processes. PM10 and PM2.5had high mass concentrations at night and low mass concentrations during the daytime on clean and dust storm days and had a unimodal distribution with a peak at 14:00 in haze. Diurnal variations in chemical composition had a unimodal distribution on clean days and a bimodal distribution on dust storm and haze days. The chemical compositions of the BC coating layer were different under different processes. The coating layers of BC were mainly NH4NO3, (NH4)2SO4, and organic matter on the clean, dust storm, and haze days, respectively. The distribution of potential sources of PM1 and its chemical components were different under different processes. The high-value area of the potential sources was mainly concentrated in the Beijing-Baoding-Shijiazhuang-Yangquan area in the southwestern portion of the site during dust storms and was mainly concentrated in Yanqing, Huailai, and Changping in the areas around the site during haze.

On the fossil and non-fossil fuel sources of carbonaceous aerosol with radiocarbon and AMS-PMF methods during winter hazy days in a rural area of North China plain

Regional transport is a key source of carbonaceous aerosol in many Chinese megacities including Beijing. The sources of carbonaceous aerosol in urban areas have been studied extensively but are poorly known in upwind rural areas. This work aims to quantify the contributions of fossil and non-fossil fuel emissions to carbonaceous aerosols at a rural site in North China Plain in winter 2016. We integrated online high resolution-time of flight-aerosol mass spectrometer (HR-TOF-AMS) observations and radiocarbon (14C) measurements of fine particles with Positive Matrix Factorization (PMF) analysis as well as Extended Gelencsér (EG) method. We found that fine particle concentration is much higher at the rural site than in Beijing during the campaign (Dec 7, 2016 to Jan 8, 2017). PMF analysis of the AMS data showed that coal-combustion related organic aerosol (CCOA + Oxidized CCOA) and more oxidized oxygenated organic aerosol (MO-OOA) contributed 48% and 30% of organic matter to non-refractory PM1 (NR-PM1) mass. About 2/3 of the OC and EC were from fossil-fuel combustion. The EG method, combining AMS-PMF and 14C data, showed that primary and secondary OC from fossil fuel contribute 35% and 22% to total carbon (TC), coal combustion emission dominates the fossil fuel sources, and biomass burning accounted for 21% of carbonaceous aerosol. In summary, our results confirm that fossil fuel combustion was the dominant source of carbonaceous aerosol during heavy pollution events in the rural areas. Significant emissions of solid fuel carbonaceous aerosols at rural areas can affect air quality in downwind cities such as Beijing and Tianjin, highlighting the benefits of energy transition from solid fuels to cleaner energy in rural areas.

Size-resolved Compositional Analysis and Source Apportionment of Submicron Aerosol during Lockdown Period Using HR-ToF-AMS

The size-resolved compositional analysis of non-refractory submicron aerosol (NR-PM1) was conducted using the Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) instrument over Pune, India during the COVID-19 lockdown period. The aerosol composition data shows the predominant presence of organics (Org) in the mass fraction followed by sulfate, ammonium, nitrate, and chloride during the pre-lockdown and lockdown periods. The size-resolved analysis showed the unimodal size distribution of organic and inorganic constituents with peaks at 550 nm, implying the dominant presence of mixed and aged aerosol species. The stoichiometric neutralization analysis showed the almost neutralized nature of submicron aerosol with an average aerosol neutralization ratio (ANR) of 0.8. The back trajectories, cluster analysis, and potential source contribution function (PSCF) showed the industrial belt located in the western part of the study location to be the potential source regions of NR-PM1. Positive matrix factorization (PMF) analyses have been applied to investigate the source apportionments of organic aerosols (OA). Four distinct OA factors, i.e., hydrocarbon-like OA (HOA), biomass burning OA (BBOA), low-volatile oxygenated OA (LVOOA), and semi-volatile oxygenated OA (SVOOA) were identified during the study period. Among these factors, HOA contributes nearly a quarter to the OA mass, and OOA accounted for nearly 60% of the total OA mass. The high-resolution positive matrix factorization (HR-PMF) analysis and the elemental ratios of H/C, O/C, and OM/OC showed distinct characteristics during different periods. The density of organic aerosol has been estimated using the elemental ratios and found to be 1.14, 1.28, and 1.35 respectively during the different lockdown periods, similar to 1.30 g/cm3 as mentioned in the literature. This study provides new insights into the chemical composition and source apportionment of the organic fraction of submicron aerosols for the first time over Pune using HR-ToF-AMS and HR-PMF.