Technical note: Use of an atmospheric simulation chamber to investigate the effect of different engine conditions on unregulated VOC-IVOC diesel exhaust emissions

Diesel exhaust emissions were introduced into an atmospheric simulation chamber and measured using thermal desorption (TD) comprehensive two-dimensional gas chromatography coupled to a flame ionisation detector (GC × GC-FID). An extensive set of measurements were performed to investigate the effect of different engine conditions (i.e. load, speed, driving scenarios) and emission control devices (with or without diesel oxidative catalyst, DOC) on the composition and abundance of unregulated exhaust gas emissions from a light-duty diesel engine, fuelled with ultra-low sulfur diesel (ULSD). A range of exhaust dilution ratios were investigated (range = 1:60 to 1:1158), simulating the chemical and physical transformations of the exhaust gas from near to downwind of an emission source. In total, 16 individual and 8 groups of compounds (aliphatics and single-ring aromatics) were measured in the exhaust gas ranging from volatile to intermediate volatility (VOC-IVOC), providing both detailed chemical speciation and groupings of compounds based on their structure and functionality. Measured VOC-IVOC emission rates displayed excellent reproducibility from replicate experiments using similar exhaust dilution ratios. However, at the extremes of the investigated exhaust dilution ratios (comparison of 1:60 and 1:1158), measured VOC-IVOC emission rates displayed some disagreement owing to poor reproducibility and highlighted the importance of replicate sample measurements. The investigated DOC was found to remove 43±10% (arithmetic mean±experimental uncertainty) of the total speciated VOC-IVOC ( ∑ SpVOC-IVOC) emissions. The compound class-dependant removal efficiencies for the investigated DOC were 39±12% and 83±3% for the aliphatics and single-ring aromatics, respectively. The DOC aliphatic removal efficiency generally decreased with increasing carbon chain length. The  ∑ SpVOC-IVOC emission rates varied significantly with different engine conditions, ranging from 70 to 9268mgkg−1 (milligrams of mass emitted per kilogram of fuel burnt).  ∑ SpVOC-IVOC emission rates generally decreased with increasing engine load and temperature, and to a lesser degree, engine speed. The exhaust gas composition changed considerably as a result of two influencing factors: engine combustion and DOC hydrocarbon (HC) removal efficiency. Increased engine combustion efficiency resulted in a greater percentage contribution of the C7 to C12 n-alkanes to the  ∑ SpVOC-IVOC emission rate. Conversely, increased DOC HC removal efficiency resulted in a greater percentage contribution of the C7 to C12 branched aliphatics to the  ∑ SpVOC-IVOC emission rate. At low engine temperatures ( < 150°C, below the working temperature of the DOC), the contribution of n-alkanes in the exhaust gas increased with increasing combustion efficiency and may be important in urban environments, as n-alkanes are more efficient at producing secondary organic aerosol (SOA) than their branched counterparts. At very high engine temperatures (maximum applied engine speed and load, engine temperature = 700°C), the n-alkane contribution increased by a factor of 1.6 times greater than that observed in the cold-start experiment (most similar to unburnt fuel) and may suggest liquid-fuel-based estimates of SOA yields may be inconsistent with exhaust SOA yields, particularly at high engine speeds and loads (i.e. high engine temperatures). Emission rates were found to be 65 times greater from a cold-start experiment than at maximum applied engine speed and load. To our knowledge, this is the first study which uses an atmospheric simulation chamber to separate the effects of the DOC and combustion efficiency on the exhaust gas composition

Size and composition measurements of background aerosol and new particle growth in a Finnish forest during QUEST 2 using an Aerodyne Aerosol Mass Spectrometer

International audienceThe study of the growth of nucleation-mode particles is important, as this prevents their loss through diffusion and allows them to reach sizes where they may become effective cloud condensation nuclei. Hyytiälä, a forested site in southern Finland, frequently experiences particle nucleation events during the spring and autumn, where particles first appear during the morning and continue to grow for several hours afterwards. As part of the QUEST 2 intensive field campaign during March and April 2003, an Aerodyne Aerosol Mass Spectrometer (AMS) was deployed alongside other aerosol instrumentation to study the particulate composition and dynamics of growth events and characterise the background aerosol. Despite the small mass concentrations, the AMS was able to distinguish the grown particles in the <100 nm regime several hours after an event and confirm that the particles were principally organic in composition. The AMS was also able to derive a mass spectral fingerprint for the organic species present, and found that it was consistent between events and independent of the mean particle diameter during non-polluted cases, implying the same species were also condensing onto the accumulation mode. The results were compared with those from offline analyses such as GC-MS and were consistent with the hypothesis that the main components were alkanes from plant waxes and the oxidation products of terpenes

Source apportionment of submicron organic aerosols at an urban site by linear unmixing of aerosol mass spectra

International audienceSubmicron ambient aerosol was characterized in summer 2005 at an urban background site in Zurich, Switzerland, during a three-week measurement campaign. Highly time-resolved samples of non-refractory aerosol components were analyzed with an Aerodyne aerosol mass spectrometer (AMS). Positive matrix factorization (PMF) was used for the first time for AMS data to identify the main components of the total organic aerosol and their sources. The PMF retrieved factors were compared to measured reference mass spectra and were correlated with tracer species of the aerosol and gas phase measurements from collocated instruments. Six factors were found to explain virtually all variance in the data and could be assigned either to sources or to aerosol components such as oxygenated organic aerosol (OOA). Our analysis suggests that at the measurement site only a small (1 originates from freshly emitted fossil fuel combustion. Other primary sources identified to be of similar or even higher importance are charbroiling (10?15%) and wood burning (~10%), along with a minor source interpreted to be influenced by food cooking (6%). The fraction of all identified primary sources is considered as primary organic aerosol (POA). This interpretation is supported by calculated ratios of the modelled POA and measured primary pollutants such as elemental carbon (EC), NOx, and CO, which are in good agreement to literature values. A high fraction (60?69%) of the measured organic aerosol mass is OOA which is interpreted mostly as secondary organic aerosol (SOA). This oxygenated organic aerosol can be separated into a highly aged fraction, OOA I, (40?50%) with low volatility and a mass spectrum similar to fulvic acid, and a more volatile and probably less processed fraction, OOA II (on average 20%). This is the first publication of a multiple component analysis technique to AMS organic spectral data and also the first report of the OOA II component

The characterisation of pollution aerosol in a changing photochemical environment

International audienceMeasurements are presented from a sampling location 50 km downwind of Greater London, UK, to investigate the timescales required for the atmospheric transformations of aerosol in urban emissions plumes in the context of photochemical age based on the benzene to toluene ratio. It is shown that particles at or around 100 nm in diameter exhibit the greatest systematic variability in chemical properties, and thus hygroscopic properties, on a timescale of 1?2 days. The smaller Aitken mode and larger accumulation mode particles exhibit less variability on these timescales, which we propose is as a result of their different residence times in the atmosphere. The larger accumulation particles have been in the atmosphere longer than the 100 nm particles and their chemistry and hygroscopic properties have been integrated over several days and potentially over several source regions. In contrast, the smaller Aitken mode particles show little systematic variability with photochemical age because their atmospheric lifetimes are short, thus chemical changes and hence changes in water affinity have not had time to occur. Increases in the particle diameter of up to 40% are observed at 90% relative humidity in the accumulation mode from the uptake of water as the particles become increasingly soluble in nature

Estudio aplicación del modelo de madurez capacidad de ingeniería. En seguridad de los sistemas (SSE-CMM) por áreas de proyecto y organización

<p>Secondary organic aerosol (SOA) particles have been found to be efficient ice-nucleating particles under the cold conditions of (tropical) upper-tropospheric cirrus clouds. Whether they also are efficient at initiating freezing under slightly warmer conditions as found in mixed-phase clouds remains undetermined. Here, we study the ice-nucleating ability of photochemically produced SOA particles with the combination of the Manchester Aerosol Chamber and Manchester Ice Cloud Chamber. Three SOA systems were tested resembling biogenic and anthropogenic particles as well as particles of different phase state. These are namely <i>α</i>-pinene, heptadecane, and 1,3,5-trimethylbenzene. After the aerosol particles were formed, they were transferred into the cloud chamber, where subsequent quasi-adiabatic cloud activation experiments were performed. Additionally, the ice-forming abilities of ammonium sulfate and kaolinite were investigated as a reference to test the experimental setup. <br/><br/> Clouds were formed in the temperature range of &minus;20 to &minus;28.6 °C. Only the reference experiment using dust particles showed evidence of ice nucleation. No ice particles were observed in any other experiment. Thus, we conclude that SOA particles produced under the conditions of the reported experiments are not efficient ice-nucleating particles starting at liquid saturation under mixed-phase cloud conditions.</p

Hygroscopicity of the submicrometer aerosol at the high-alpine site Jungfraujoch, 3580 m a.s.l., Switzerland

Data from measurements of hygroscopic growth of submicrometer aerosol with a hygroscopicity tandem differential mobility analyzer (HTDMA) during four campaigns at the high alpine research station Jungfraujoch, Switzerland, are presented. The campaigns took place during the years 2000, 2002, 2004 and 2005, each lasting approximately one month. Hygroscopic growth factors (&lt;i&gt;GF&lt;/i&gt;, i.e. the relative change in particle diameter from dry diameter, &lt;i&gt;D&lt;/i&gt;&lt;sub&gt;0&lt;/sub&gt;, to diameter measured at higher relative humidity, RH) are presented for three distinct air mass types, namely for: 1) free tropospheric winter conditions, 2) planetary boundary layer influenced air masses (during a summer period) and 3) Saharan dust events (SDE). The &lt;i&gt;GF&lt;/i&gt; values at 85% RH (&lt;i&gt;D&lt;/i&gt;&lt;sub&gt;0&lt;/sub&gt;=100 nm) were 1.40&amp;plusmn;0.11 and 1.29&amp;plusmn;0.08 for the first two situations while for SDE a bimodal &lt;i&gt;GF&lt;/i&gt; distribution was often found. No phase changes were observed when the RH was varied between 10–90%, and the continuous water uptake could be well described with a single-parameter empirical model. The frequency distributions of the average hygroscopic growth factors and the width of the retrieved growth factor distributions (indicating whether the aerosol is internally or externally mixed) are presented, which can be used for modeling purposes. &lt;br&gt;&lt;br&gt; Measurements of size resolved chemical composition were performed with an aerosol mass spectrometer in parallel to the &lt;i&gt;GF&lt;/i&gt; measurements. This made it possible to estimate the apparent ensemble mean &lt;i&gt;GF&lt;/i&gt; of the organics (&lt;i&gt;GF&lt;/i&gt;&lt;sub&gt;org&lt;/sub&gt;) using inverse ZSR (Zdanovskii-Stokes-Robinson) modeling. &lt;i&gt;GF&lt;/i&gt;&lt;sub&gt;org&lt;/sub&gt; was found to be ~1.20 at &lt;i&gt;a&lt;/i&gt;&lt;sub&gt;w&lt;/sub&gt;=0.85, which is at the upper end of previous laboratory and field data though still in agreement with the highly aged and oxidized nature of the Jungfraujoch aerosol

Relating hygroscopicity and composition of organic aerosol particulate matter

A hygroscopicity tandem differential mobility analyzer (HTDMA) was used to measure the water uptake (hygroscopicity) of secondary organic aerosol (SOA) formed during the chemical and photochemical oxidation of several organic precursors in a smog chamber. Electron ionization mass spectra of the non-refractory submicron aerosol were simultaneously determined with an aerosol mass spectrometer (AMS), and correlations between the two different signals were investigated. SOA hygroscopicity was found to strongly correlate with the relative abundance of the ion signal m/z 44 expressed as a fraction of total organic signal (f44). m/z 44 is due mostly to the ion fragment CO2+ for all types of SOA systems studied, and has been previously shown to strongly correlate with organic O/C for ambient and chamber OA. The analysis was also performed on ambient OA from two field experiments at the remote site Jungfraujoch, and the megacity Mexico City, where similar results were found. A simple empirical linear relation between the hygroscopicity of OA at subsaturated RH, as given by the hygroscopic growth factor (GF) or "ϰorg" parameter, and f44 was determined and is given by ϰorg = 2.2 × f44 − 0.13. This approximation can be further verified and refined as the database for AMS and HTDMA measurements is constantly being expanded around the world. The use of this approximation could introduce an important simplification in the parameterization of hygroscopicity of OA in atmospheric models, since f44 is correlated with the photochemical age of an air mass

Relating hygroscopicity and composition of organic aerosol particulate matter

A hygroscopicity tandem differential mobility analyzer (HTDMA) was used to measure the water uptake (hygroscopicity) of secondary organic aerosol (SOA) formed during the chemical and photochemical oxidation of several organic precursors in a smog chamber. Electron ionization mass spectra of the non-refractory submicron aerosol were simultaneously determined with an aerosol mass spectrometer (AMS), and correlations between the two different signals were investigated. SOA hygroscopicity was found to strongly correlate with the relative abundance of the ion signal m/z 44 expressed as a fraction of total organic signal (f44). m/z 44 is due mostly to the ion fragment CO2+ for all types of SOA systems studied, and has been previously shown to strongly correlate with organic O/C for ambient and chamber OA. The analysis was also performed on ambient OA from two field experiments at the remote site Jungfraujoch, and the megacity Mexico City, where similar results were found. A simple empirical linear relation between the hygroscopicity of OA at subsaturated RH, as given by the hygroscopic growth factor (GF) or "κorg" parameter, and f44 was determined and is given by κorg=2.2×f44−0.13. This approximation can be further verified and refined as the database for AMS and HTDMA measurements is constantly being expanded around the world. The use of this approximation could introduce an important simplification in the parameterization of hygroscopicity of OA in atmospheric models, since f44 is correlated with the photochemical age of an air mass

A method for extracting calibrated volatility information from the FIGAERO-HR-ToF-CIMS and its experimental application

The Filter Inlet for Gases and AEROsols (FIGAERO) is an inlet specifically designed to be coupled with the Aerodyne High-Resolution Time-of-Flight Chemical Ionization Mass Spectrometer (HR-ToF-CIMS). The FIGAERO-HR-ToF-CIMS provides simultaneous molecular information relating to both the gas- and particle-phase samples and has been used to extract vapour pressures (VPs) of the compounds desorbing from the filter whilst giving quantitative concentrations in the particle phase. However, such extraction of vapour pressures of the measured particle-phase components requires use of appropriate, well-defined, reference compounds. Vapour pressures for the homologous series of polyethylene glycols (PEG) ((H-(O-CH2CH2)n-OH) for n = 3 to n = 8), covering a range of vapour pressures (VP) (10-1 to 10-7 Pa) that are atmospherically relevant, have been shown to be reproduced well by a range of different techniques, including Knudsen Effusion Mass Spectrometry (KEMS). This is the first homologous series of compounds for which a number of vapour pressure measurement techniques have been found to be in agreement, indicating the utility as a calibration standard, providing an ideal set of benchmark compounds for accurate characterization of the FIGAERO for extracting vapour pressure of measured compounds in chambers and the real atmosphere. To demonstrate this, single-component and mixture vapour pressure measurements are made using two FIGAERO-HR-ToF-CIMS instruments based on a new calibration determined from the PEG series. VP values extracted from both instruments agree well with those measured by KEMS and reported values from literature, validating this approach for extracting VP data from the FIGAERO. This method is then applied to chamber measurements, and the vapour pressures of known products are estimated