9 research outputs found
Feasibility of coupling a thermal/optical carbon analyzer to a quadrupole mass spectrometer for enhanced PM2.5 speciation
A thermal/optical carbon analyzer (TOA), normally used for quantification of organic carbon (OC) and elemental carbon (EC) in PM2.5 (fine particulate matter) speciation networks, was adapted to direct thermally evolved gases to an electron impact quadrupole mass spectrometer (QMS), creating a TOA-QMS. This approach produces spectra similar to those obtained by the Aerodyne aerosol mass spectrometer (AMS), but the ratios of the mass to charge (m/z) signals differ and must be remeasured using laboratory-generated standards. Linear relationships are found between TOA-QMS signals and ammonium (NH4+), nitrate (NO3-), and sulfate (SO42-) standards. For ambient samples, however, positive deviations are found for SO42-, compensated by negative deviations for NO3-, at higher concentrations. This indicates the utility of mixed-compound standards for calibration or separate calibration curves for low and high ion concentrations. The sum of the QMS signals across all m/z after removal of the NH4+, NO3-, and SO42- signals was highly correlated with the carbon content of oxalic acid (C2H2O4) standards. For ambient samples, the OC derived from the TOA-QMS method was the same as the OC derived from the standard IMPROVE_A TOA method. This method has the potential to reduce complexity and costs for speciation networks, especially for highly polluted urban areas such as those in Asia and Africa.Implications: Ammonium, nitrate, and sulfate can be quantified by the same thermal evolution analysis applied to organic and elemental carbon. This holds the potential to replace multiple parallel filter samples and separate laboratory analyses with a single filter and a single analysis to account for a large portion of the PM2.5 mass concentration
Field intercomparison of the gas/particle partitioning of oxygenated organics during the Southern Oxidant and Aerosol Study (SOAS) in 2013
Mercury, PM 2.5 and gaseous co-pollutants in the Ohio River Valley region: Preliminary results from the Athens supersite
Abstract This paper presents preliminary results from an ongoing air quality project at a rural super site in Athens, Ohio . This is due in part to a series of unusual weather events featuring transport predominantly from the north, northeast, and southeast. The effects of the remnants of hurricanes Frances and Ivan on air quality data are also apparent during this month. This paper also presents results of PM 2.5 , gaseous co-pollutant, and meteorological measurements. Results are compiled into daily and monthly averages to display diurnal and seasonal patterns. Low background concentrations with frequent pollution episodes make this rural site an excellent location to capture transport events into and out of the Ohio River Valley.
A Chemical Ionization High-Resolution Time-of-Flight Mass Spectrometer Coupled to a Micro Orifice Volatilization Impactor (MOVI-HRToF-CIMS) for Analysis of Gas and Particle-Phase Organic Species
Comprehensive characterization of atmospheric organic carbon at a forested site
Atmospheric organic compounds are central to key chemical processes that influence air quality, ecological health, and climate. However, longstanding difficulties in predicting important quantities such as organic aerosol formation and oxidant lifetimes indicate that our understanding of atmospheric organic chemistry is fundamentally incomplete, probably due in part to the presence of organic species that are unmeasured using standard analytical techniques. Here we present measurements of a wide range of atmospheric organic compoundsāincluding previously unmeasured speciesātaken concurrently at a single site (a ponderosa pine forest during summertime) by five state-of-the-art mass spectrometric instruments. The combined data set provides a comprehensive characterization of atmospheric organic carbon, covering a wide range in chemical properties (volatility, oxidation state, and molecular size), and exhibiting no obvious measurement gaps. This enables the first construction of a measurement-based local organic budget, highlighting the high emission, deposition, and oxidation fluxes in this environment. Moreover, previously unmeasured species, including semivolatile and intermediate-volatility organic species (S/IVOCs), account for one-third of the total organic carbon, and (within error) provide closure on both OH reactivity and potential secondary organic aerosol formation
Impact of Thermal Decomposition on Thermal Desorption Instruments: Advantage of Thermogram Analysis for Quantifying Volatility Distributions of Organic Species
We
present results from a high-resolution chemical ionization time-of-flight
mass spectrometer (HRToF-CIMS), operated with two different thermal
desorption inlets, designed to characterize the gas and aerosol composition.
Data from two field campaigns at forested sites are shown. Particle
volatility distributions are estimated using three different methods:
thermograms, elemental formulas, and measured partitioning. Thermogram-based
results are consistent with those from an aerosol mass spectrometer
(AMS) with a thermal denuder, implying that thermal desorption is
reproducible across very different experimental setups. Estimated
volatilities from the detected elemental formulas are much higher
than from thermograms since many of the detected species are thermal
decomposition products rather than actual SOA molecules. We show that
up to 65% of citric acid decomposes substantially in the FIGAEROāCIMS,
with ā¼20% of its mass detected as gas-phase CO<sub>2</sub>,
CO, and H<sub>2</sub>O. Once thermal decomposition effects on the
detected formulas are taken into account, formula-derived volatilities
can be reconciled with the thermogram method. The volatility distribution
estimated from partitioning measurements is very narrow, likely due
to signal-to-noise limits in the measurements. Our findings indicate
that many commonly used thermal desorption methods might lead to inaccurate
results when estimating volatilities from observed ion formulas found
in SOA. The volatility distributions from the thermogram method are
likely the closest to the real distributions