Soot Particle Aerosol Mass Spectrometer Research Articles

Chemical properties and single-particle mixing state of soot aerosol in Houston during the TRACER campaign

Abstract. A high-resolution soot particle aerosol mass spectrometer (SP-AMS) was used to selectively measure refractory black carbon (rBC) and its associated coating material using both the ensemble size-resolved mass spectral mode and the event trigger single particle (ETSP) mode in Houston, Texas, in summer 2022. This study was conducted as part of the Department of Energy Atmospheric Radiation Measurement (ARM) program's TRacking Aerosol Convection interactions ExpeRiment (TRACER) field campaign. The study revealed an average (±1σ) rBC concentration of 103 ± 176 ng m−3. Additionally, the coatings on the BC particles were primarily composed of organics (59 %; 219 ± 260 ng m−3) and sulfate (26 %; 94 ± 55 ng m−3). Positive matrix factorization (PMF) analysis of the ensemble mass spectra of BC-containing particles resolved four distinct types of soot aerosol, including an oxidized organic aerosol (OOABC,PMF) factor associated with processed primary organic aerosol, an inorganic sulfate factor (SO4,BC,PMF), an oxidized rBC factor (O-BCPMF), and a mixed mineral dust–biomass burning aerosol factor with significant contribution from potassium (K-BBBC,PMF). Additionally, K-means clustering analysis of the single-particle mass spectra identified eight different clusters, including soot particles enriched in hydrocarbon-like organic aerosol (HOABC,ETSP), sulfate (SO4,BC,ETSP), two types of rBC, OOA (OOABC,ETSP), chloride (ClBC,ETSP), and nitrate (NO3,BC,ETSP). The single-particle measurements demonstrate substantial variation in BC coating thickness with coating-to-rBC mass ratios ranging from 0.1 to 100. The mixing state index (χ), which denotes the degree of homogeneity of the soot aerosol, varied from 4 % to 94 % with a median of 40 %, indicating that the aerosol population lies in between internal and external mixing but has large temporal and source type variability. In addition, a significant fraction of BC-containing particles, a majority enriched with oxidized organics and sulfate, exhibit sufficiently high κ values and diameters conducive to activation as cloud nuclei under atmospherically relevant supersaturation conditions. This finding bears significance in comprehending the aging processes of rBC-containing particles and their activation into cloud droplets. Our analysis highlights the complex nature of soot aerosol and underscores the need to comprehend its variability across different environments for accurate assessment of climate change.

Black carbon instrument responses to laboratory generated particles

Accurate measurement of black carbon (BC) particles is vital for climate models as well as air quality assessments. While the need for BC particle measurement has been recognized, standardization of instruments and procedures for ambient measurement is still underway. In this study, we used laboratory generated soot particles to assess nine instruments targeting BC mass concentration measurement. The measurement matrix included different BC concentrations (ranging from atmospheric levels to combustion emission levels), different particle coatings, two particle sources (gas burner and spark generator) and two dilution methods. The nine instruments included six different models: aethalometers AE33 and MA200, thermo-optical OC-EC analysis, multi-angle absorption photometer MAAP 5012, photoacoustic instrument MSS, and soot particle aerosol mass spectrometer SP-AMS. The main discrepancy we observed was that the SP-AMS results were systematically lower, approximately only half of the BC measured by other instruments. A portion of this is explained by particle losses in the aerodynamic lens of the SP-AMS and the parameters used in the data analysis. Some smaller discrepancies were identified for the other instruments, but overall, the median values from were within 25 % of each other. Instruments’ operation principles and covered concentration ranges need to be carefully considered especially in emission measurements where the aerosols can have high temporal variation as well as high BC concentrations. In general, the results can decrease the uncertainties in climate and air quality studies by providing tools for more accurate and comparable BC measurements and when the existing BC data is interpreted.

Source apportionment of soot particles and aqueous-phase processing of black carbon coatings in an urban environment

Abstract. The impacts of soot particles on climate and human health depend on the concentration of black carbon (BC) as well as the thickness and composition of the coating material, i.e., organic and inorganic compounds internally mixed with BC. In this study, the size-resolved chemical composition of BC-containing aerosol was measured using a high-resolution soot particle aerosol mass spectrometer (SP-AMS) during wintertime in Fresno, California, a location influenced by abundant combustion emissions and frequent fog events. Concurrently, particle optical properties were measured to investigate the BC absorption enhancement. Positive matrix factorization (PMF) analysis was performed on the SP-AMS mass spectral measurements to explore the sources of soot particles and the atmospheric processes affecting the properties of BC coatings. The analysis revealed that residential woodburning and traffic are the dominant sources of soot particles. Alongside primary soot particles originating from biomass burning (BBOABC) and vehicles (HOABC) two distinct types of processed BC-containing aerosol were identified: fog-related oxidized organic aerosol (FOOABC) and winter-background OOABC (WOOABC). Both types of OOABC showed evidence of having undergone aqueous processing, albeit with differences. The concentration of FOOABC was substantially elevated during fog events, indicating the formation of aqueous secondary organic aerosol (aqSOA) within fog droplets. On the other hand, WOOABC was present at a relatively consistent concentration throughout the winter and was likely related to the formation of secondary organic aerosol (SOA) in both the gas phase and aerosol liquid water. By comparing the chemical properties and temporal variations in FOOABC and WOOABC, we gain insights into the key aging processes of BC aerosol. It was found that aqueous-phase reactions facilitated by fog droplets had a significant impact on the thickness and chemical composition of BC coatings, thereby affecting the light absorption and hygroscopic properties of soot particles. These findings underscore the important role of chemical reactions occurring within clouds and fogs and influencing the climate forcing of BC aerosol in the atmosphere.

Chemically distinct particle-phase emissions from highly controlled pyrolysis of three wood types

Abstract. Wood pyrolysis is a distinct process that precedes combustion and contributes to biomass and biofuel burning gas-phase and particle-phase emissions. Pyrolysis is defined as the thermochemical degradation of wood, the products of which can be released directly or undergo further reaction during gas-phase combustion. To isolate and study the processes and emissions of pyrolysis, a custom-made reactor was used to uniformly heat small blocks of wood in a nitrogen atmosphere. Pieces of maple, Douglas fir, and oak wood (maximum of 155 cm3) were pyrolyzed in a temperature-controlled chamber set to 400, 500, or 600 ∘C. Real-time particle-phase emissions were measured with a soot particle aerosol mass spectrometer (SP-AMS) and correlated with simultaneous gas-phase emission measurements of CO. Particle and gas emissions increased rapidly after inserting a wood sample, remained high for tens of minutes, and then dropped rapidly leaving behind char. The particulate mass-loading profiles varied with elapsed experiment time, wood type and size, and pyrolysis chamber temperature. The chemical composition of the emitted particles was organic (C, H, O), with negligible black carbon or nitrogen. The emitted particles displayed chemical signatures unique to pyrolysis and were notably different from flaming or smoldering wood combustion. The most abundant fragment ions in the mass spectrum were CO+ and CHO+, which together made up 23 % of the total aerosol mass on average, whereas CO2+ accounted for less than 4 %, in sharp contrast with ambient aerosol where CO2+ is often a dominant contributor. The mass spectra also showed signatures of levoglucosan and other anhydrous sugars. The fractional contribution of m/z 60, traditionally a tracer for anhydrous sugars including levoglucosan, to total loading (f60) was observed to be between 0.002 and 0.039, similar to previous observations from wildfires and controlled wood fires. Atomic ratios of oxygen and hydrogen to carbon, O:C and H:C as calculated from AMS mass spectra, varied between 0.41–0.81 and 1.06–1.57, respectively, with individual conditions lying within a continuum of O:C and H:C for wood's primary constituents: cellulose, hemicellulose, and lignin. This work identifies the mass spectral signatures of particle emissions directly from pyrolysis, including f60 and the CO+/CO2+ ratio, through controlled laboratory experiments in order to help in understanding the importance of pyrolysis emissions in the broader context of wildfires and controlled wood fires.

Characterization of volatile organic compounds and submicron organic aerosol in a traffic environment

Abstract. Urban air consists of a complex mixture of gaseous and particulate species from anthropogenic and biogenic sources that are further processed in the atmosphere. This study investigated the characteristics and sources of volatile organic compounds (VOCs) and submicron organic aerosol (OA) in a traffic environment in Helsinki, Finland, in late summer. The anthropogenic VOCs (aVOCs; aromatic hydrocarbons) and biogenic VOCs (bVOCs; terpenoids) relevant for secondary-organic-aerosol formation were analyzed with an online gas chromatograph mass spectrometer, whereas the composition and size distribution of submicron particles was measured with a soot particle aerosol mass spectrometer. This study showed that aVOC concentrations were significantly higher than bVOC concentrations in the traffic environment. The largest aVOC concentrations were measured for toluene (campaign average of 1630 ng m−3) and p/m xylene (campaign average of 1070 ng m−3), while the dominating bVOC was α-pinene (campaign average of 200 ng m−3). For particle-phase organics, the campaign-average OA concentration was 2.4 µg m−3. The source apportionment analysis extracted six factors for OA. Three OA factors were related to primary OA sources – traffic (24 % of OA, two OA types) and a coffee roastery (7 % of OA) – whereas the largest fraction of OA (69 %) consisted of oxygenated OA (OOA). OOA was divided into less oxidized semi-volatile OA (SV-OOA; 40 % of OA) and two types of low-volatility OA (LV-OOA; 30 %). The focus of this research was also on the oxidation potential of the measured VOCs and the association between VOCs and OA in ambient air. Production rates of the oxidized compounds (OxPR) from the VOC reactions revealed that the main local sources of the oxidation products were O3 oxidation of bVOCs (66 % of total OxPR) and OH radical oxidation of aVOCs and bVOCs (25 % of total OxPR). Overall, aVOCs produced a much smaller portion of the oxidation products (18 %) than bVOCs (82 %). In terms of OA factors, SV-OOA was likely to originate from biogenic sources since it correlated with an oxidation product of monoterpene, nopinone. LV-OOA consisted of highly oxygenated long-range or regionally transported OA that had no correlation with local oxidant concentrations as it had already spent several days in the atmosphere before reaching the measurement site. In general, the main sources were different for VOCs and OA in the traffic environment. Vehicle emissions impacted both VOC and OA concentrations. Due to the specific VOCs attributed to biogenic emissions, the influence of biogenic emissions was more clearly detected in the VOC concentrations than in OA. In contrast, the emissions from the local coffee roastery had a distinctive mass spectrum for OA, but they could not be seen in the VOC measurements due to the measurement limitations for the large VOC compounds. Long-range transport increased the OA concentration and oxidation state considerably, while its effect was observed less clearly in the VOC measurements due to the oxidation of most VOC in the atmosphere during the transport. Overall, this study revealed that in order to properly characterize the impact of different emission sources on air quality, health, and climate, it is of importance to describe both gaseous and particulate emissions and understand how they interact as well as their phase transfers in the atmosphere during the aging process.

Evolution characteristic of atmospheric black carbon particles at a coastal site in the Pearl River Delta, China

The mixing of black carbon (BC) with secondary materials is a major uncertainty source in assessing its radiative forcing. However, current understanding of the formation and evolution of various BC components is limited, particularly in the Pearl River Delta, China. This study measured submicron BC-associated nonrefractory materials and the total submicron nonrefractory materials using a soot particle aerosol mass spectrometer and a high-resolution time-of-flight aerosol mass spectrometer, respectively, at a coastal site in Shenzhen, China. Two distinct atmospheric conditions were also identified to further explore the distinctive evolution of BC-associated components: polluted period (PP) and clean period (CP). Comparing the components of two particles, we found that more-oxidized organic factor (MO-OOA) prefers to form on BC during PP rather CP. The formation of MO-OOA on BC (MO-OOABC) was affected by both enhanced photochemical processes and nocturnal heterogeneous processes. Enhanced photo-reactivity of BC, photochemistry during the daytime, and heterogeneous reaction at nighttime were potential pathways for MO-OOABC formation during PP. The fresh BC surface was favorable for the formation of MO-OOABC. Our study shows the evolution of BC-associated components under different atmospheric conditions, which should be considered in regional climate models to improve the assessment of the climate effects of BC.

Characterizing formation mechanisms of secondary aerosols on black carbon in a megacity in South China

Refractory black carbon (rBC) aerosols emitted from incomplete combustion are important climate forcers. Understanding the chemical characteristics and evolution of rBC-related components is particularly crucial to assess rBC environmental impacts. Here, we explored the chemical components of rBC in Shenzhen, China, using a soot-particle aerosol mass spectrometer (SP-AMS). The observations showed that the rBC coating was mainly composed of secondary aerosols with an average mass contribution of 84.7 %. Among them, secondary organic coating occupied ∼57.7 % of the total coating mass. Exploration of the relationship between secondary organic aerosol (SOA) coating and Ox (=NO2 + O3, an indicator of the extent of photochemical processing) showed that SOA coating was generated mainly through photochemical oxidation during the day. Similarly, sulfate coating, with a small mass fraction of 0.9 %, was also dominated by photochemical oxidation. In contrast, nitrate coating responded positively to ambient relative humidity, especially at night, indicating that it was driven by heterogeneous reactions. In addition, the increased ratio of nitrate on rBC to bulk nitrate at night suggested that black carbon surface could facilitate nocturnal nitrate formation.

Chemical properties, sources and size-resolved hygroscopicity of submicron black-carbon-containing aerosols in urban Shanghai

Abstract. Refractory black carbon (rBC) aerosols play an important role in air quality and climate change, yet highly time-resolved and detailed investigations on the physicochemical properties of rBC and its associated coating are still scarce. In this work, we used a laser-only Aerodyne soot particle aerosol mass spectrometer (SP-AMS) to exclusively measure rBC-containing (rBCc) particles, and we compared their properties with those of the total nonrefractory submicron particles (NR-PM1) measured in parallel by a high-resolution AMS (HR-AMS) in Shanghai. Observations showed that, overall, rBC was thickly coated, with an average mass ratio of coating to rBC core (RBC) of ∼5.0 (±1.7). However, the ratio of the mass of the rBC-coating species to the mass of those species in NR-PM1 was only 19.1 (±4.9) %; sulfate tended to condense preferentially on non-rBC particles, so the ratio of the sulfate on rBC to the NR-PM1 sulfate was only 7.4 (±2.2) %, while the majority (72.7±21.0 %) of the primary organic aerosols (POA) were associated with rBC. Positive matrix factorization revealed that organics emitted from cooking did not coat rBC, and a portion of the organics that coated rBC was from biomass burning; such organics were unidentifiable in NR-PM1. Small rBCc particles were predominantly from traffic, while large-sized ones were often mixed with secondary components and typically had a thick coating. Sulfate and secondary organic aerosol (SOA) species were generated mainly through daytime photochemical oxidation (SOA formation, likely associated with in situ chemical conversion of traffic-related POA to SOA), while nocturnal heterogeneous formation was dominant for nitrate; we also estimated an average time of 5–19 h for those secondary species to coat rBC. During a short period that was affected by ship emissions, particles were characterized as having a high vanadium concentration (on average 6.3±3.1 ng m−3) and a mean vanadium/nickel mass ratio of 2.0 (±0.6). Furthermore, the size-resolved hygroscopicity parameter (κrBCc) of rBCc particles was obtained based on their full chemical characterization, and was parameterized as κrBCc(x)=0.29–0.14 × exp⁡(-0.006×x) (where x ranges from 150 to 1000 nm). Under critical supersaturations (SSC) of 0.1 % and 0.2 %, the D50 values were 166 (±16) and 110 (±5) nm, respectively, and 16 (±3) % and 59 (±4) %, respectively, of the rBCc particles by number could be activated into cloud condensation nuclei (CCN). Our findings are valuable for advancing the understanding of BC chemistry as well as the effective control of atmospheric BC pollution.

Characterization of particle sources and comparison of different particle metrics in an urban detached housing area, Finland

Particulate matter (PM) is emitted from various anthropogenic sources in urban areas affecting the local air quality. The aim of this study was to characterize the sources influencing air quality in detached house area in the Helsinki metropolitan area in Finland, and secondly, to explore the additional value of new particle physical properties to assess the impact of residential combustion on air quality. Measurements were conducted in an urban detached housing area between January and April 2019. Measured particle physical properties were particle number (PN), particle mass (PM1) and lung deposited surface area (LDSA) concentrations and number size distributions. In addition, particle chemical composition was measured using a soot particle aerosol mass spectrometer (SP-AMS; organic compounds, inorganic ions) and an aethalometer (black carbon (BC)). Concentrations of selected monosaccharide anhydrides and polycyclic aromatic hydrocarbons were analysed from the PM10 filter samples. The sources and characteristics of organic aerosol was investigated by applying positive matrix factorization to the mass spectra measured with the SP-AMS. Based on the variations in the measured particle physical parameters, chemical species and meteorology, the measurement period was divided into three sub periods dominated by urban background, wood burning and long-range transport (LRT) aerosols. Highest pollutant concentrations were measured during the wood burning and LRT periods. Wood burning increased the concentrations of all measured species, but the differences were most significant to levoglucosan, benzo(a)pyrene, BC and PM1 that had 12, 10, 6.4 and 3.6 times larger mean concentrations during the wood burning period compared to the urban background period, respectively. LRT affected significantly levoglucosan, PM1 and BC concentrations, since LRT pollutants partly originated from open biomass fires in Eastern Europe. The impact of local wood burning and LRT was quite small to particle number concentrations, whereas LDSA concentrations and size distributions were affected by traffic, wood combustion emissions and LRT. BC concentration correlated with the LDSA concentration during all periods suggesting a common origin. Particle number concentration was a good indicator of local combustion, especially traffic emissions, while the PM1 mass concentration together with secondary particle material was a good measure for the LRT pollutants. Benzo(a)pyrene was found to be a good indicator of local wood burning, but it was not detected in LRT biomass combustion particles.

Chemical and physical characterization of oil shale combustion emissions in Estonia

In this study, oil shale combustion emission measurements were conducted in a 60 kW th Circulating Fluidized Bed combustion test facility located in a laboratory-type environment. A comprehensive set of instruments including a nitrate-ion-based Chemical Ionization Atmospheric Pressure interface Time-of-Flight Mass Spectrometer, a Soot-Particle Aerosol Mass Spectrometer, and a Potential Aerosol Mass (PAM) chamber was utilized to investigate the chemical composition and concentrations of primary and secondary emissions in oil shale combustion. In addition, the size distribution of particles (2.5–414 nm) as well as concentration and composition of gaseous precursors were characterized. Altogether 12 different experiments were conducted. Primary emissions were studied in seven experiments and aged emissions using PAM chamber in five experiments. Combustion temperatures and solid fuel circulation rates varied between different experiments, and it was found that the burning conditions had a large impact on gaseous and particulate emissions. The majority of the combustion particles were below 10 nm in size during good burning whereas in poor burning conditions the emitted particles were larger and size distributions with 2–3 particle modes were detected. The main submicron particle chemical component was particulate organic matter (POM), followed by sulfate, chloride, nitrate, and ammonium. The secondary particulate matter formed in the PAM chamber was mostly POM and the concentration of POM was many orders of magnitude higher in aged aerosol compared to primary emissions. A significant amount of aromatic volatile organic compounds (VOCs) was measured as well. VOCs have the potential to go through gas-to-particle conversion during the oxidation process, explaining the observed high concentrations of aged POM. During good combustion, when VOC emissions were lower, over 80% of SO 2 was oxidized either to gaseous H 2 SO 4 (37%) or particulate sulfate (46%) in the PAM chamber, which mimic the atmospheric processes taken place in the ambient air after few days of emission. • Oil Shale was combusted in a 60-kW th laboratory facility. • Combustion temperature had a large influence on exhaust emissions. • Poor burning produced larger particles and hence larger mass concentrations. • High amount of secondary particle matter was formed during ageing experiments. • SO 2 , sulfuric acid clusters and particulate sulfate were determined.

Aqueous aging of secondary organic aerosol coating onto black carbon: Insights from simultaneous L-ToF-AMS and SP-AMS measurements at an urban site in southern China

Secondary organic aerosol (SOA) in the atmosphere can be formed from the gas phase precursors and evolve in the particle phase. Compared to numerous studies on gas phase oxidation of volatile organic compounds (VOCs), the evolution of OA and corresponding mechanisms in the particle phase are still unclear. In this study, a thermodenuder (TD) was coupled with both a long time-of-flight aerosol mass spectrometer (L-ToF-AMS) and a soot particle aerosol mass spectrometer (SP-AMS) at an urban site in southern China during wintertime of 2018, to explore whether there is significant difference for OA evolution on black carbon (BC) aerosols. The OA measured by L-ToF-AMS and SP-AMS were resolved into different primary and secondary factors, with the OA factors on BC particles showed different volatilities to that on the bulk aerosol. The more-oxidized oxygenated OA (MO-OOA, an agent of aged SOA) exhibited a unique preference on BC particles compared to other OA components. The abundant transition metals detected on BC particles was possibly the catalyser for the transformation from less oxidized OOA (LO-OOA, an agent of fresh SOA) to MO-OOA in aerosol aqueous-phase on BC particles and thus facilitates SOA formation. More studies are needed to further explore the potential role of BC and transition metals as catalysers for OA aging and the co-benefit of BC and transition metals pollution control on SOA reduction in the atmosphere.

Polycyclic aromatic hydrocarbons from cooking emissions

Air pollution studies have often overlooked the contribution from cooking to the particle-bound polycyclic aromatic hydrocarbons (PAHs) in the ambient environment, despite cooking emissions have been identified as an important source of organic aerosol in most urban areas, known as the cooking-like organic aerosol factor (i.e., COA). In this study, a Long-Time-of-Flight (LToF) soot particle aerosol mass spectrometer (SP-AMS) was deployed to evaluate the impact of cooking emissions on outdoor particle-bound PAHs levels during a summer campaign in 2019 in Xi'an China. Combined with the robust receptor model, cooking emission was found to be the major source of ambient PAHs, on average, accounting for 90% of PAHs, 9 times higher than traffic (10%). The ambient cooking PAH profile was well correlated (r2 of 0.87) with that for frying oil fume, suggesting cooking oil was the major source of PAHs instead of the food being cooked. We further evaluated the health risk associated with the cooking PAHs and estimated the cooking PAH levels in some of the major cities in the world where COA factor has been reported. The results show the particle-bound PAHs from cooking can be an important source of ambient PAHs in most Chinese cities. The findings from this study hold important implications for public health and are informing for policymakers.

Influence of regional emission controls on the chemical composition, sources, and size distributions of submicron aerosols: Insights from the 2014 Nanjing Youth Olympic Games

High-intensity emission controls were implemented in Nanjing and in 8 surrounding cities to ensure good air quality during the 2014 summer Youth Olympic Games (YOG). An Aerodyne soot-particle aerosol mass spectrometer (SP-AMS) was deployed at a downwind site of downtown Nanjing to investigate the chemical composition, sources, and size distribution of submicron aerosols (PM1), in response to emission control policies. However, results show that emission controls played a negligible role in reducing PM1 concentration during the YOG period, yet primary precursors such as NOx and SO2 were decreased by 10–20%. Low wind speed, high relative humidity, and high ozone (O3) concentration likely play a significant role in the production and accumulation of the oxygenated organic aerosol (OOA) and the secondary inorganic aerosols (SIA) in summer Nanjing. We propose that long-term regional emission reduction could be a solution for future air pollution mitigation strategies in downwind cities of the YRD region, and that seasonal meteorological characteristics in a specific region should be considered before emission control policies are made.

Primary and Secondary Organic Nitrate in Northwest China: A Case Study

Particle-bound organic nitrate is ubiquitous in the atmosphere, but its primary emission and secondary formation processes are poorly understood and are, therefore, generally ignored in models. In this study, based on the ambient measurements and a series of combustion experiments, we found that the nitrate functionality from organic nitrate (primary + secondary) accounted for 20%–53% of the total NO3 signal measured with a long-time-of-flight (LToF) soot particle aerosol mass spectrometer (SP-AMS) in northwestern China in mid-November 2020. In particular, secondary organic nitrate accounted for 17% and 36% of the measured NO3 during the haze and reference periods, respectively. It was further estimated that secondary organic nitrate, on average, accounted for 46% of the total organic matter (or 18% of PM2.5) during the haze period, representing a significant portion of the secondary organic aerosol, while primary organic nitrate, mostly from biomass burning, was estimated to account for 8%–9% of the total organic matter (3%–5% of PM2.5). Moreover, we showed that photochemical (OH-initiated + elevated NO2) formation of organic nitrate was probably a more important pathway than the nighttime chemistry (NO3 initiated), which is in great contrast to that in European areas where nighttime chemistry was found to be the dominant pathway.

Sources of black carbon at residential and traffic environments obtained by two source apportionment methods

Abstract. This study investigated the sources of black carbon (BC) at two contrasting urban environments in Helsinki, Finland: residential area and street canyon. The measurement campaign in the residential area was conducted in winter–spring 2019, whereas in the street canyon the measurements were carried out in autumn 2015. The sources of BC were explored by using positive matrix factorization (PMF) for the organic and refractory black carbon (rBC) mass spectra collected with a soot particle aerosol mass spectrometer (SP-AMS). Based on the PMF analysis, two sites had different local BC sources; the largest fraction of BC originated from biomass burning at the residential site (38 %) and from the vehicular emissions in the street canyon (57 %). Also, the mass size distribution of BC diverged at the sites as BC from traffic was found at the particle size of ∼100–150 nm whereas BC from biomass combustion was detected at ∼300 nm. At both sites, a large fraction of BC was associated with urban background or long-range-transported BC indicated by the high oxidation state of organics related to those PMF factors. The results from the PMF analysis were compared with the source apportionment from the Aethalometer model calculated with two pairs of absorption Ångström values. It was found that several PMF factors can be attributed to wood combustion and fossil fuel fraction of BC provided by the Aethalometer model. In general, the Aethalometer model showed less variation between the sources within a day than PMF, indicating that it was less responsive to the fast changes in the BC sources at the site, or it could not distinguish between as many sources as PMF due to the similar optical properties of the BC sources. The results of this study increase understanding of the limitations and validity of the BC source apportionment methods in different environments. Moreover, this study advances the current knowledge of BC sources and especially the contribution of residential combustion in urban areas.

Technical note: A new approach to discriminate different black carbon sources by utilising fullerene and metals in positive matrix factorisation analysis of high-resolution soot particle aerosol mass spectrometer data

Abstract. Atmospheric aerosol particles are known to have detrimental effects on human health and climate. Black carbon is an important constituent of atmospheric aerosol particulate matter (PM), emitted from incomplete combustion. Source apportionment of BC is very important, to evaluate the influence of different sources. The high-resolution soot particle aerosol mass spectrometer (HR-SP-AMS) instrument uses a laser vaporiser, which allows the real-time detection and characterisation of refractory black carbon (rBC) and its internally mixed particles such as metals, coating species, and rBC subcomponents in the form of HOA + fullerene. In this case study, the soot data were collected by using HR-SP-AMS during Guy Fawkes Night on 5 November 2014. Positive matrix factorisation was applied to positively discriminate between different wood-burning and bonfire sources for the first time, which no existing black carbon source apportionment technique is currently able to do. Along with this, the use of the fullerene signals in differentiating between soot sources and the use of metals as a tracer for fireworks has also been investigated, which did not significantly contribute to the rBC concentrations. The addition of fullerene signals and successful positive matrix factorisation (PMF) application to HR-SP-AMS data apportioned rBC into more than two sources. These bonfire sources are HOA + fullerene, biomass burning organic aerosol, more oxidised oxygenated organic aerosol (MO-OOA), and non-bonfire sources such as hydrocarbon-like OA and domestic burning. The result of correlation analysis between HR-SP-AMS data and previously published Aethalometer, MAAP, and CIMS data provides an effective way of gaining insights into the relationships between the variables and provide a quantitative estimate of the source contributions to the BC budget during this period. This research study is an important demonstration of using HR-SP-AMS for the purpose of BC source apportionment.

Chemical Characteristics and Sources of Water-Soluble Organic Nitrogen Species in PM2.5 in Nanjing, China

Water-soluble organic nitrogen (WSON) is an important component of PM2.5 which may affect air quality, climate and human health. Herein, one-year field samples of atmospheric PM2.5 (June 2017–May 2018) were collected in northern Nanjing. Chemical characterization of PM2.5 major components as well as WSON were conducted, and WSON composition and sources were further investigated via measurements by a Aerodyne soot particle aerosol mass spectrometer (SP-AMS) as well as positive matrix factorization (PMF). Inorganic ions, mainly consisting of ammonium, sulfate, and nitrate, were found to dominate PM2.5 mass (58.7%), followed by organic matter (OM) (22.6%), and elemental carbon (EC) (2.1%). Water-soluble OM dominated OM (65.1%), and its temporal variation was closely correlated with that of secondary organic matter, while time series of water-insoluble OM concentrations correlated tightly with that of primary organic matter. Average WSON concentration was 2.15 μg/m3, which was highest in winter and lowest in summer. Correlation analysis of WSON with PM2.5 components also indicated that WSON was mainly from secondary sources. SP-AMS revealed that WSON mass spectrum was composed of CxHyNp+ (91.2%) and CxHyOzNp+ (8.8%), indicating dominance of amines and other oxygenated ON compounds. PMF analysis resolved two primary sources (traffic, biomass burning) and two secondary sources (less-oxidized and more-oxidized factors) of WSOM and WSON, and the secondary source dominated both WSOM and WSON. Contribution of the more-oxidized ON factor was very high in winter, and the less-oxidized factor was significant in summer, indicating a likely important role of aqueous-phase processing in winter as well as photochemical oxidation in summer to WSON.

Elemental analysis of oxygenated organic coating on black carbon particles using a soot-particle aerosol mass spectrometer

Abstract. Chemical characterization of organic coatings is important to advance our understanding of the physio-chemical properties and environmental fate of black carbon (BC) particles. The soot-particle aerosol mass spectrometer (SP-AMS) has been utilized for this purpose in recent field studies. The laser vaporization (LV) scheme of the SP-AMS can heat BC cores gradually until they are completely vaporized, during which organic coatings can be vaporized at temperatures lower than that of the thermal vaporizer (TV) used in a standard high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) that employs flash vaporization. This work investigates the effects of vaporization schemes on fragmentation and elemental analysis of known oxygenated organic species using three SP-AMS instruments. We show that LV can reduce fragmentation of organic molecules. Substantial enhancement of C2H3O+/CO2+ and C2H4O2+ signals was observed for most of the tested species when the LV scheme was used, suggesting that the observational frameworks based on the use of HR-ToF-AMS field data may not be directly applicable for evaluating the chemical evolution of oxygenated organic aerosol (OOA) components coated on ambient BC particles. The uncertainties of H:C and O:C determined using the improved-ambient (I-A) method for both LV and TV approaches were similar, and scaling factors of 1.10 for H:C and 0.89 for O:C were determined to facilitate more direct comparisons between observations from the two vaporization schemes. Furthermore, the I-A method was updated based on the multilinear regression model for the LV scheme measurements. The updated parameters can reduce the relative errors of O:C from −26.3 % to 5.8 %, whereas the relative errors of H:C remain roughly the same. Applying the scaling factors and the updated parameters for the I-A method to ambient data, we found that even though the time series of OOA components determined using the LV and TV schemes are strongly correlated at the same location, OOA coatings were likely less oxygenated compared to those externally mixed with BC.

Soot Particle Agglomeration Inlet (SPAI) for Enabling Online Chemical Composition Measurement of Nanoparticles with the Aerosol Mass Spectrometer

Nanoparticles are a topic of interest because of their effects on human health and the climate, but the current options for evaluating their chemical composition—one of the key properties that determine the mechanisms of these effects—remain very limited and often require long collection times. For example, the Soot Particle Aerosol Mass Spectrometer (SP-AMS) is an instrument that measures the chemical properties of particles in real time, but sampling loss fixes its lower particle size limit at 50 nm, thus excluding nanoparticles. Hence, we developed the Soot Particle Agglomeration Inlet (SPAI), an addition to the SP-AMS that enables it to detect and analyze nanoparticles by attaching them to the surfaces of artificially generated soot particles. We characterized and optimized the soot generation and the soot–nanoparticle agglomeration via laboratory testing and then assessed the SPAI’s performance using silver nanoparticles as the test aerosol. The SPAI increased the SP-AMS’s capability to detect the silver nanoparticles by 35 times, demonstrating its potential in resolving issues related to analyzing the chemical composition of nanoparticles, either as an enhancement of the SP-AMS or as an addition to other sample pretreatment systems.

Particle detection using the dual-vaporizer configuration of the soot particle Aerosol Mass Spectrometer (SP-AMS)

The Aerodyne Soot Particle Aerosol Mass Spectrometer (SP-AMS) can operate with one or both of two particle vaporizers: (1) the standard resistively heated tungsten vaporizer (TV) for detection of n...