Mass spectrometric measurements of ambient aerosols yield organic spectra that are a mix of nucleated particles, freshly emitted particles from many sources, and particles which have undergone some ...amount of processing (condensation, oxidative reaction, cloud processing, etc.). Further understanding of the important sources and processes for organic aerosols requires deconvolution of the organic fraction of ambient aerosols. A well-known source apportionment technique, Positive Matrix Factorization (PMF), has been applied to Aerodyne aerosol mass spectrometer (Q-AMS and HR-ToF-AMS) datasets acquired in Pittsburgh (2002), Mexico City (2003), Blodgett Forest (2007) and other sites. Sensitivity analysis of the Pittsburgh case is performed with synthetic datasets and characterizes the behaviour of PMF with AMS datasets. PMF is a least-squares fitting method for source apportionment commonly applied to speciated aerosol datasets (Paatero, Chemomet. Intell. Lab. Sys. 1997, 37, 23-35). The structure and precision of the AMS dataset are significantly different from datasets compiled from previous measurements of multiple aerosol components (metals, organic and elemental carbon, ions, etc.), are very large (~300 points per sample, with ~3000-10,000 samples for these campaigns), and fragmentation of molecules during ionization gives each mass spectrum strongly interrelated data. Additionally, because the Aerodyne AMS does not detect elemental carbon or metals (common and important in most PMF analyses), application of this technique to AMS data yields significantly different source profiles than in previous PMF studies. Each site has a hydrocarbon-like organic aerosol (HOA) factor that is likely primary OA and multiple oxygenated organic aerosol (OOA) factors that are likely secondary OA, and biomass burning organic aerosol (BBOA) can be separated in some locations. The OOA factors always include one highly-oxygenated factor (OOA-I) that resembles the spectrum of fulvic acid and less-oxygenated factors that resemble spectra from chamber studies of SOA. Assignment of factor spectra to these categories is aided by comparison to spectra collected by many research groups using the Aerodyne AMS to measure individual compounds, reactions in smog chambers, and primary emission sources. These spectra have been compiled in a publicly-available database (http://cires.colorado.edu/jimenez-group/AMSsd/spectra.html).
Air travel and freight shipping by air are becoming increasingly important and are expected to continue to expand. The resulting increases in the local concentrations of pollutants, including ...particulate matter (PM), volatile organic compounds (VOCs), and nitrogen oxides (NOX), can have negative impacts on regional air quality, human health and can impact climate change. In order to construct valid emission inventories, accurate measurements of aircraft emissions are needed. These measurements must be done both at the engine exit plane (certification) and downwind following the rapid cooling, dilution and initial atmospheric processing of the exhaust plume. We present here results from multiple field experiments which include the Experiment to Characterize Volatile Aerosol and Trace Species Emissions (EXCAVATE) and the four Aircraft Particle Emissions eXperiments (APEX- 1/Atlanta/2/3) which characterized gas and particle emissions from both stationary or in-use aircraft. Emission indices (EIs) for NOx and VOCs and for particle number concentration, refractory PM (black carbon soot) and volatile PM (primarily sulfate and organic) particles are reported. Measurements were made at the engine exit plane and at several downstream locations (10 and 30 meters) for a number of different engine types and engine thrust settings. A significant fraction of organic particle mass is composed of low volatility oil-related compounds and is not combustion related, potentially emitted by vents or heated surfaces within aircraft engines. Advected plumes measurements from in-use aircraft show that the practice of reduced thrust take-offs has a significant effect on total NOx and soot emitted in the vicinity of the airport. The measurements reported here represent a first observation of this effect and new insights have been gained with respect to the chemical processing of gases and particulates important to the urban airshed.
The organic particulate matter measured using the aerosol mass spectrometer has been deconvolved into multiple organic components using positive matrix factorization techniques including ...hydrocarbon-like organic aerosol (HOA) and oxygenated organic aerosol (OOA). The correlation between OOA and Ox (Ox = NO2 + O3) will be explored. The ratio of SOA production to ozone production should depend on the VOC composition since they are both photochemical processes. VOC emissions in the Houston Ship Channel and Galveston Bay area are diverse: urban, marine diesel, petrochemical, industrial. This analysis will challenge the understanding of SOA production in the context of urban emissions. Organic aerosol can be further oxidized in the atmosphere. One product of that oxidation which may represent a particle to gas process is formic acid. The processes contributing to gas phase production will be evaluated and upper limits for the potential heterogenous production will be presented.
Observations in Mexico City during the MILAGRO 2006 campaign and in Houston during the TexAQS 2000 campaign have shown correlations between Ox (Ox = O3 + NO2) and the oxidized component of organic ...aerosol (OOA), which is interpreted as secondary organic aerosol (SOA). Such a correlation is expected given that ozone production and SOA formation are both fundamentally related to the oxidation of VOCs. We quantitatively investigate the observed correlation between OOA and Ox by comparison with the calculated ratio of the production rates of SOA and ozone. P(SOA)/P(Ox) is calculated using measurements of ambient VOCs, predicted concentrations of unmeasured compounds from vehicle exhaust, and known atmospheric oxidation mechanisms
Organic matter usually accounts for a large fraction of the fine particle mass in rural and remote atmospheres. However, little is known about the sources and properties of this material. Here we ...report findings on the characteristics and the major types of organic aerosols (OA) in urban downwind, high elevation, forested, and marine atmospheres based on analyses of more than 20 highly time resolved AMS datasets sampled from various locations in the mid-latitude Northern Hemisphere. Organic aerosol components are extracted from these datasets using a custom multiple component mass spectral analysis technique and the Positive Matrix Factorization (PMF) method. These components are evaluated according to their extracted mass spectra and correlations to aerosol species, such as sulfate, nitrate, and elemental carbon, and gas-phase tracer compounds, such as CO and NOx. We have identified a hydrocarbon-like organic aerosol (HOA) component similar in mass spectra to the hydrocarbon substances observed at urban locations. We have also identified several oxygenated OA (OOA) components that show different fragmentation patterns and oxygen to carbon ratios in their mass spectra. Two OOA components i? a highly oxygenated that has mass spectrum resembling that of fulvic acid (a model compound representative for highly processed/oxidized organics in the environment) and a less oxygenated OOA component, whose spectrum is dominated with ions that are mainly associated with carbonyls and alcohols, are very frequently observed at various rural/remote sites. The oxygenated OOA component is more prevalent at downwind sites influenced by urban transport and the less oxygenated shows correlation to biogenic chamber OA at some locations. Compared to the total OOA concentration, HOA is generally very small and accounts for < 10% of the total OA mass at rural/remote sites. The comparisons between the concentrations of HOA and primary OA (POA) that would be predicted according to inert primary emission tracers (e.g., EC and CO) suggest that dilution of urban POA is the main reason for its low concentration at rural/remote sites. In addition, case studies will be presented to evaluate the implications of intercontinental and regional transport of air pollution for the background organic aerosol composition at a high elevation site (the Whistler Mountain Summit, Canada) of North America. Finally, an attempt will be made to address the relative importance of secondary vs. primary organic aerosol (SOA vs. POA) and biogenic vs. anthropogenic OA.
Mexico City Metropolitan Area (MCMA) is a mega-city environment with significant air pollution. Emissions of primary particles and secondary particle precursors are high and build up in the boundary ...layer during the night with the concentrations peaking during the early morning. Daily photochemistry alters the chemical, physical, and optical properties of these primary particles. The Aerodyne mobile laboratory, outfitted with a suite of gas and particle instruments, investigated the processing of these primary particles at the T0 site as part of the Mexico City Metropolitan Area (MCMA) component of the MILAGRO campaign (March 2006). Aerosol particle mass, chemistry (bulk and surface PAHs), absorption and scattering, and size-distributions (mobility and vacuum aerodynamic) were measured. Simultaneous measurements by the AMS and SMPS instruments on mobility-selected particles yielded the particle mass, volume, density, composition, dynamic shape factor, and fractal dimension. Early morning primary particle emissions were dominated by fractal particles containing significant surface bound PAHs, similar in morphology and composition to diesel-generated particles. During the morning, these particles were observed to grow in mass and become more spherical via gas-to-particle condensation of photochemical products (oxidized organic compounds and ammonium nitrate). Particles with fractal morphologies and surface bound PAH signals were no longer evident after late morning and at down wind locations. Emission ratios, correlations with carbon monoxide, and organic aerosol chemical classifications will be presented. The rapid processing and fate of these primary particles will be discussed with an emphasis on gaining insight into the processing mechanisms.
