Determination of PM1 Sources at a Prague Background Site during the 2012–2013 Period Using PMF Analysis of Combined Aerosol Mass Spectra

Two intensive measurement campaigns using a compact time-of-flight aerosol mass spectrometer were carried out at the suburban site in Prague (Czech Republic) in summer (2012) and winter (2013). The aim was to determine the aerosol sources of the NR-PM1 fraction by PMF analysis of organic (OA) and inorganic aerosol mass spectra. Firstly, an analysis of the OA mass spectra was performed. Hydrocarbon-like OA (HOA), biomass burning OA (BBOA), and two types of oxygenated OA (OOA1) and (OOA2) were identified in summer. In winter, HOA, BBOA, long-range oxygenated OA (LROOA), and local oxygenated OA (LOOA) were determined. The identified HOA and BBOA factors were then used as additional input for the subsequent ME-2 analysis of the combined organic and inorganic spectra. This analysis resulted in six factors in both seasons. All of the previously reported organic factors were reidentified and expanded with the inorganic part of the spectra in both seasons. Two predominantly inorganic factors ammonium sulphate (AMOS) and ammonium nitrate (AMON) were newly identified in both seasons. Despite very similar organic parts of the mass profiles, the daily cycles of HOA and LOOA differed significantly in winter. It appears that the addition of the inorganic part of the mass profile, in some cases, reduces the ability of the model to identify physically meaningful factors.

Substantial organic impurities at the surface of synthetic ammonium sulfate particles

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 (from 200 nm to 500 nm) 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 Spectrometry (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, they likely originate from the commercial AS crystals. For AS particle sizes ranging from 200 nm to 500 nm, the total mass fraction of organic (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 surface with a 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.

Mass spectral characterization of secondary organic aerosol from urban cooking and vehicular sources

In the present work, we conducted experiments of secondary organic aerosol (SOA) formation from urban cooking and vehicular sources to characterize the mass spectral features of primary organic aerosol (POA) and SOA using an high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Our results showed that the cooking styles have a greater impact on aged COA (cooking organic aerosol) mass spectra than oxidation conditions. However, the oxidation conditions affect the aged HOA (hydrocarbon-like OA) spectra more significantly than vehicle operating conditions. In our study, we use mass spectra similarity analysis and positive matrix factorization (PMF) analysis to establish the POA and SOA mass spectra of these two sources. These mass spectra are used as source constraints in a multilinear engine (ME-2) model to apportion the OA (organic aerosol) sources in the atmosphere. Compared with the traditional ambient PMF results, the improved ME-2 model can better quantify the contribution of POA and SOA from cooking and vehicular sources. Our work, for the first time, establishes the vehicle and cooking SOA source profiles, and can be further used in the OA source apportionment in the ambient atmosphere.

Design, characterization, and first field deployment of a novel aircraft-based aerosol mass spectrometer combining the laser ablation and flash vaporization techniques

In this paper, we present the design, development, and characteristics of the novel aerosol mass spectrometer ERICA (ERC Instrument for Chemical composition of Aerosols) and selected results from the first aircraft-borne field deployment. The instrument combines two well-established methods of real-time in-situ measurements of fine particle chemical composition. The first method is the single particle laser ablation technique (here with a frequency-quadrupled Nd:YAG laser at λ = 266 nm). The other method is a combination of flash vaporization and electron impact ionization (like the Aerodyne aerosol mass spectrometer). The aerosol sample can be analyzed with both methods, each using time-of-flight mass spectrometry. By means of the laser ablation, single particles are qualitatively analyzed (including the refractory components) while the flash vaporization and electron impact ionization technique provides quantitative information on the non-refractory components (i.e., particulate sulfate, nitrate, ammonia, organics, and chloride) of small particle ensembles. These techniques are implemented in two consecutive instrument stages within a common sample inlet and a common vacuum chamber. At its front end, the sample air containing the aerosol particles is continuously injected via an aerodynamic lens (ADL). All particles which are not ablated by the Nd:YAG laser in the first instrument stage continue their flight until they reach the second instrument stage and impact on the vaporizer surface (operated at 600 °C). The ERICA is capable of detecting single particles with vacuum aerodynamic diameters (dva) between ~ 180 nm and 3170 nm (d50 cut-off). The chemical characterization of single particles is achieved by recording cations and anions with a bipolar time-of-flight mass spectrometer (B-ToF-MS). For the measurement of non-refractory components, the particle size range extends from approximately 120 nm to 3.5 µm (d50 cut-off; dva), and the cations are detected with a C-ToF-MS (compact time-of-flight mass spectrometer). The compact dimensions of the instrument are such that the ERICA can be deployed on aircraft, ground stations, or mobile laboratories . During its first deployments the instrument operated fully automated during 11 research flights on the Russian high-altitude research aircraft M-55 Geophysica from ground pressure and temperature up to 20 km altitude at 55 hPa and ambient temperatures as low as −86 °C.

A Systematic Re-evaluation of Methods for Quantification of Bulk Particle-phase Organic Nitrates Using Real-time Aerosol Mass Spectrometry

Organic nitrate (RONO2) formation in the atmosphere represents a sink of NOx (NOx = NO + NO2) and termination of the NOx/HOx (HOx = HO2 + OH) ozone formation and radical propagation cycles, can act as a NOx reservoir transporting reactive nitrogen, and contributes to secondary organic aerosol formation. While some fraction of RONO2 is thought to reside in the particle phase, particle-phase organic nitrates (pRONO2) are infrequently measured and thus poorly understood. There is an increasing prevalence of aerosol mass spectrometer (AMS) instruments, which have shown promise for determining quantitative total organic nitrate functional group contribution to aerosols. A simple approach that relies on the relative intensities of NO+ and NO2+ ions in the AMS spectrum, the calibrated NOx+ ratio for NH4NO3, and the inferred ratio for pRONO2 has been proposed as a way to apportion the total nitrate signal to NH4NO3 and pRONO2. This method is increasingly being applied to field and laboratory data. However, the methods applied have been largely inconsistent and poorly characterized, and therefore, a detailed evaluation is timely. Here, we compile an extensive survey of NOx+ ratios measured for various pRONO2 compounds and mixtures from multiple AMS instruments, groups, and laboratory and field measurements. We show that, in the absence of pRONO2 standards, the pRONO2 NOx+ ratio can be estimated using a ratio referenced to the calibrated NH4NO3 ratio, a so-called Ratio-of-Ratios method (RoR = 2.75 ± 0.41). We systematically explore the basis for quantifying pRONO2 (and NH4NO3) with the RoR method using ground and aircraft field measurements conducted over a large range of conditions. The method is compared to another AMS method (positive matrix factorization, PMF) and other pRONO2 and related (e.g., total gas + particle RONO2) measurements, generally showing good agreement/correlation. A broad survey of ground and aircraft AMS measurements shows a pervasive trend of higher fractional contribution of pRONO2 to total nitrate with lower total nitrate concentrations, which generally corresponds to shifts from urban-influenced to rural/remote regions. Compared to ground campaigns, observations from all aircraft campaigns showed substantially lower pRONO2 contributions at mid ranges of total nitrate (0.01–0.1 up to 2–5 μg m−3), suggesting that the balance of effects controlling NH4NO3 and pRONO2 formation and lifetimes — such as higher humidity, lower temperatures, greater dilution, different sources, higher particle acidity, and pRONO2 hydrolysis (possibly accelerated by particle acidity) — favors lower pRONO2 contributions for those environments and altitudes sampled.

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

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.