Quartz Filter Samples Research Articles

Intercomparison of thermal–optical carbon measurements by Sunset and Desert Research Institute (DRI) analyzers using the IMPROVE_A protocol

Abstract. Thermal–optical analysis (TOA) is a class of methods widely used for determining organic carbon (OC) and elemental carbon (EC) in atmospheric aerosols collected on filters. Results from TOA vary not only with differences in operating protocols for the analysis, but also with details of the instrumentation with which a given protocol is carried out. Three models of TOA carbon analyzers have been used for the IMPROVE_A protocol in the past decade within the Chemical Speciation Network (CSN). This study presents results from intercomparisons of these three analyzer models using two sets of CSN quartz filter samples, all analyzed using the IMPROVE_A protocol with reflectance charring correction. One comparison was between the Sunset model 5L (Sunset) analyzers and the Desert Research Institute (DRI) model 2015 (DRI-2015) analyzers using 4073 CSN samples collected in 2017. The other comparison was between the Sunset and the DRI model 2001 (DRI-2001) analyzers using 303 CSN samples collected in 2007. Both comparisons showed a high degree of inter-model consistency in total carbon (TC) and the major carbon fractions, OC and EC, with a mean bias within 5 % for TC and OC and within 12 % for EC. Relatively larger and diverse inter-model discrepancies (mean biases of 5 %–140 %) were found for thermal subfractions of OC and EC (i.e., OC1–OC4 and EC1–EC3), with better agreement observed for subfractions with higher mass loadings and smaller within-model uncertainties. Optical charring correction proved critical in bringing OC and EC measurements by different TOA analyzer models into agreement. Appreciable inter-model differences in EC between Sunset and DRI-2015 (mean bias ±SD of 21.7 %±12.2 %) remained for ∼5 % of the 2017 CSN samples; examination of these analysis thermograms revealed that the optical measurement (i.e., filter reflectance and transmittance) saturated in the presence of strong absorbing materials on the filter (e.g., EC), leaving an insufficient dynamic range for the detection of carbon pyrolysis and thus no optical charring correction. Differences in instrument parameters and configuration, possibly related to disagreement in OC and EC subfractions, are also discussed. Our results provide a basis for future studies of uncertainties associated with the TOA analyzer model transition in assessing long-term trends of CSN carbon data. Further investigations using these data are warranted, focusing on the demonstrated inter-model differences in OC and EC subfractions. The within- and inter-model uncertainties are useful for model performance evaluation.

No more waste at the elemental analysis of airborne particulate matter on quartz fibre filters

Particulate matter (PM) is the major environmental pollutant. Its elemental composition is routinely monitored. Inductively coupled plasma mass spectroscopy (ICPMS) is commonly applied after a PM sample has been digested by an acid during a microwave treatment. In this case, sample preparation procedure is laborious, sometimes incomplete and produces toxic waste. In this paper we show that direct sample introduction to ICPMS by laser ablation (LA-ICPMS) is of huge advantage. Minimal quantity of a sample is required for the analysis (<1 cm2) and no chemical waste is produced. The study focused on the most universal and widely used quartz fibre filter samples and we show that LA-ICPMS can be successfully applied for the determination of the elemental composition of such samples. Some effort is, however, still needed to develop an autosampler for the LA-ICPMS system and to provide commercial matrix-matched standards for this application to be implemented in environment laboratories worldwide.

Observations of sesquiterpenes and their oxidation products in central Amazonia during the wet and dry seasons

Biogenic volatile organic compounds (BVOCs) from the Amazon forest region represent the largest source of organic carbon emissions to the atmosphere globally. These BVOC emissions dominantly consist of volatile and intermediate-volatility terpenoid compounds that undergo chemical transformations in the atmosphere to form oxygenated condensable gases and secondary organic aerosol (SOA). We collected quartz filter samples with 12 h time resolution and performed hourly in situ measurements with a semi-volatile thermal desorption aerosol gas chromatograph (SV-TAG) at a rural site ("T3") located to the west of the urban center of Manaus, Brazil as part of the Green Ocean Amazon (GoAmazon2014/5) field campaign to measure intermediate-volatility and semi-volatile BVOCs and their oxidation products during the wet and dry seasons. We speciated and quantified 30 sesquiterpenes and 4 diterpenes with mean concentrations in the range 0.01-6.04 ngm-3 (1-670ppqv). We estimate that sesquiterpenes contribute approximately 14 and 12% to the total reactive loss of O3 via reaction with isoprene or terpenes during the wet and dry seasons, respectively. This is reduced from ~ 50-70 % for within-canopy reactive O3 loss attributed to the ozonolysis of highly reactive sesquiterpenes (e.g., β-caryophyllene) that are reacted away before reaching our measurement site. We further identify a suite of their oxidation products in the gas and particle phases and explore their role in biogenic SOA formation in the central Amazon region. Synthesized authentic standards were also used to quantify gas- and particle-phase oxidation products derived from β-caryophyllene. Using tracer-based scaling methods for these products, we roughly estimate that sesquiterpene oxidation contributes at least 0.4-5 % (median 1 %) of total submicron OA mass. However, this is likely a low-end estimate, as evidence for additional unaccounted sesquiterpenes and their oxidation products clearly exists. By comparing our field data to laboratory-based sesquiterpene oxidation experiments we confirm that more than 40 additional observed compounds produced through sesquiterpene oxidation are present in Amazonian SOA, warranting further efforts towards more complete quantification.

A non-destructive optical color space sensing system to quantify elemental and organic carbon in atmospheric particulate matter on Teflon and quartz filters

Optical color space sensing proved to be a valuable method in particle characterization since it provides a non-destructive, fast, and cost-efficient way to estimate organic and elemental carbon (OC, EC) in atmospheric particulate matter. Here we expand and validate the previous work with the measurement of the CIE-Lab optical color space system and development of a multi-parameter reference calibration model to estimate EC/OC collected on Teflon and quartz filters. Analysis of approximately 500 Teflon and quartz filter samples demonstrated that the described method could be a robust way to estimate EC and OC loadings on the filters. The results showed that the correlation coefficients between predicted and measured loadings for the model-estimated EC and OC were 0.951 (CV (RMSE) = 15.1%) and 0.908 (CV (RMSE) = 20.7%) on Teflon filters and 0.948 (CV (RMSE) = 17.4%) and 0.895 (CV (RMSE) = 21.1%) on quartz filters respectively. The model cross-validation also provided good agreement between the predicted EC and OC loadings on Teflon and quartz filters and the NIOSH thermal-optical method. It was also found that the mixing state of the chemical composition and sources of OC could interfere the absorption and scattering of light, which results in a model estimation uncertainty that should be evaluated within the model estimations. The non-destructive and low analytical cost of the method, when applied to Teflon filters that are used for mass measurement are a cost effective means for estimating EC and OC exposures and concentrations in health studies and large-scale monitoring campaigns.

Predicting ambient aerosol thermal–optical reflectance measurements from infrared spectra: elemental carbon

Abstract. Elemental carbon (EC) is an important constituent of atmospheric particulate matter because it absorbs solar radiation influencing climate and visibility and it adversely affects human health. The EC measured by thermal methods such as thermal–optical reflectance (TOR) is operationally defined as the carbon that volatilizes from quartz filter samples at elevated temperatures in the presence of oxygen. Here, methods are presented to accurately predict TOR EC using Fourier transform infrared (FT-IR) absorbance spectra from atmospheric particulate matter collected on polytetrafluoroethylene (PTFE or Teflon) filters. This method is similar to the procedure developed for OC in prior work (Dillner and Takahama, 2015). Transmittance FT-IR analysis is rapid, inexpensive and nondestructive to the PTFE filter samples which are routinely collected for mass and elemental analysis in monitoring networks. FT-IR absorbance spectra are obtained from 794 filter samples from seven Interagency Monitoring of PROtected Visual Environment (IMPROVE) sites collected during 2011. Partial least squares regression is used to calibrate sample FT-IR absorbance spectra to collocated TOR EC measurements. The FT-IR spectra are divided into calibration and test sets. Two calibrations are developed: one developed from uniform distribution of samples across the EC mass range (Uniform EC) and one developed from a uniform distribution of Low EC mass samples (EC &lt; 2.4 μg, Low Uniform EC). A hybrid approach which applies the Low EC calibration to Low EC samples and the Uniform EC calibration to all other samples is used to produce predictions for Low EC samples that have mean error on par with parallel TOR EC samples in the same mass range and an estimate of the minimum detection limit (MDL) that is on par with TOR EC MDL. For all samples, this hybrid approach leads to precise and accurate TOR EC predictions by FT-IR as indicated by high coefficient of determination (R2; 0.96), no bias (0.00 μg m−3, a concentration value based on the nominal IMPROVE sample volume of 32.8 m3), low error (0.03 μg m−3) and reasonable normalized error (21 %). These performance metrics can be achieved with various degrees of spectral pretreatment (e.g., including or excluding substrate contributions to the absorbances) and are comparable in precision and accuracy to collocated TOR measurements. Only the normalized error is higher for the FT-IR EC measurements than for collocated TOR. FT-IR spectra are also divided into calibration and test sets by the ratios OC/EC and ammonium/EC to determine the impact of OC and ammonium on EC prediction. We conclude that FT-IR analysis with partial least squares regression is a robust method for accurately predicting TOR EC in IMPROVE network samples, providing complementary information to TOR OC predictions (Dillner and Takahama, 2015) and the organic functional group composition and organic matter estimated previously from the same set of sample spectra (Ruthenburg et al., 2014).

Composition and Source Apportionment of Organic Aerosol in Beirut, Lebanon, During Winter 2012

Fine organic aerosols were collected at a semi-urban site in Beirut, Lebanon, from 28 January to 12 February 2012 as part of the Emission and Chemistry of Organic Carbon in East Mediterranean-Beirut (ECOCEM-Beirut). A total of 20 quartz filter samples were collected on a 12 h basis using a high-volume sampler and were analyzed using a GC/MS technique. Levoglucosan was the major most abundant single component with an average value of 306 ng.m−3, followed by saturated and unsaturated carboxylic acids and sugars with average values of 234 and 118 ng.m−3, respectively. Reported values for other carboxylic acids, polycyclic aromatic hydrocarbons, and biogenic secondary organic aerosols (BSOA) were 87, 33 and 21 ng.m−3, respectively. Compared to a similar field campaign conducted in summer 2011, levoglucosan concentrations were lower in summer by a factor of 6, due to the use of wood burning for residential heating in winter. Concentrations of saturated and unsaturated carboxylic acids, other carboxylic acids, and BSOA were higher in summer by a factor of 3, 2, and 7, respectively. Higher concentrations observed for BSOA and other dicarboxylic acids during summer are due to higher biogenic emissions and greater photochemical activity in summer. Copyright 2013 American Association for Aerosol Research

Gas-Particle Partitioning of Primary Organic Aerosol Emissions: (2) Diesel Vehicles

Experiments were performed to investigate the gas-particle partitioning of primary organic aerosol (POA) emissions from two medium-duty (MDDV) and three heavy-duty (HDDV) diesel vehicles. Each test was conducted on a chassis dynamometer with the entire exhaust sampled into a constant volume sampler (CVS). The vehicles were operated over a range of driving cycles (transient, high-speed, creep/idle) on different ultralow sulfur diesel fuels with varying aromatic content. Four independent yet complementary approaches were used to investigate POA gas-particle partitioning: artifact correction of quartz filter samples, dilution from the CVS into a portable environmental chamber, heating in a thermodenuder, and thermal desorption/gas chromatography/mass spectrometry (TD-GC-MS) analysis of quartz filter samples. During tests of vehicles not equipped with diesel particulate filters (DPF), POA concentrations inside the CVS were a factor of 10 greater than ambient levels, which created large and systematic partitioning biases in the emissions data. For low-emitting DPF-equipped vehicles, as much as 90% of the POA collected on a quartz filter from the CVS were adsorbed vapors. Although the POA emission factors varied by more than an order of magnitude across the set of test vehicles, the measured gas-particle partitioning of all emissions can be predicted using a single volatility distribution derived from TD-GC-MS analysis of quartz filters. This distribution is designed to be applied directly to quartz filter data that are the basis for existing emissions inventories and chemical transport models that have implemented the volatility basis set approach.

Long-term size-segregated particle (PM10, PM2.5, PM1) characterization study at Melpitz -- influence of air mass inflow, weather conditions and season

Size-segregated high-volume (HV) quartz filter samples were collected daily at the Melpitz rural site in Germany for PM10 (November 1992 until April 2012), and for PM2.5 and PM1 (January 2003 until April 2012, PM1 sampled every sixth day). The samples were analysed for mass concentration (gravimetrically), water-soluble ions (ion-chromatography) and since 2003 for organic carbon (OC) and elemental carbon (EC) (thermography). The long-term measurements first show a decreasing trend for PM10 (1993–2000) followed by a second period (2001–2011) with a mean mass concentration of about 22.4 μgm−3 and an inter-annual variation of about ± 2.9 μgm−3 (13% fluctuation margin). The absolute sulphate and calcium concentration (for the full period), as well as the EC concentration (time after 2003) decrease by about 50, 75 and 30% for PM10, respectively. The nitrate concentration remains constant all the time. For the daily objective weather type classification (OWTC, 1993–2002) the highest PM10 concentration was found for South-East (SE) and the lowest for North-West (NW) wind direction with 44 and 24 μgm−3, respectively. These concentrations decrease for 2003–2011 in comparison to 1993–2002 by about 21% and 26%, respectively. The highest PM10, PM2.5 and PM1 concentrations (2003–2011) were found for SE and the lowest for NW wind direction with about 34 and 17 μgm−3 (PM10), 28 and 19 μgm−3 (PM2.5) and 22 and 11 μgm−3 (PM1), respectively. The relative content of sulphate, OC and EC was the highest for SE wind direction. A differentiation into four categories for winter (Wi) and summer (Su) and air mass inflow from West (W) and East (E) was carried out. The highest PM concentrations were observed for WiE with the highest inter-annual fluctuation. In this category sulphate contents are largest. The lowest concentrations where found for SuW. The means for WiE show the strongest relative decreases, e.g. in PM10 sulphate (1993–2011) and EC (2003–2011) by about 60% and 40%, respectively. Nitrate is an indicator for NOx motor-car emissions. It shows a typical variation with maximum values in the middle of the week, especially for air mass inflow from West. In contrast, chloride mostly originating from sea spray doesn’t show such a concentration pattern. The PM2.5/PM10 as well the PM1/PM10-ratio have the highest median (0.878 and 0.654) during WiE and the lowest (0.718 and 0.578) during SuW, respectively. For the ratio PM2.5/PM10 a slightly increasing trend was found (about 0.71 and 0.83 for 1995 and 2011, respectively). The increase is stronger in summer than in winter.

Gas-particle partitioning of primary organic aerosol emissions: (1) Gasoline vehicle exhaust

The gas-particle partitioning of the primary organic aerosol (POA) emissions from fifty-one light-duty gasoline vehicles (model years 1987–2012) was investigated at the California Air Resources Board Haagen–Smit Laboratory. Each vehicle was operated over the cold-start unified cycle on a chassis dynamometer and its emissions were sampled using a constant volume sampler. Four independent yet complementary approaches were used to investigate POA gas-particle partitioning: sampling artifact correction of quartz filter data, dilution from the constant volume sampler into a portable environmental chamber, heating in a thermodenuder, and thermal desorption/gas chromatography/mass spectrometry analysis of quartz filter samples. This combination of techniques allowed gas-particle partitioning measurements to be made across a wide range of atmospherically relevant conditions – temperatures of 25–100 °C and organic aerosol concentrations of <1–600 μg m−3. The gas-particle partitioning of the POA emissions varied continuously over this entire range of conditions and essentially none of the POA should be considered non-volatile. Furthermore, for most vehicles, the low levels of dilution used in the constant volume sampler created particle mass concentrations that were greater than a factor of 10 or higher than typical ambient levels. This resulted in large and systematic partitioning biases in the POA emission factors compared to more dilute atmospheric conditions, as the POA emission rates may be over-estimated by nearly a factor of four due to gas-particle partitioning at higher particle mass concentrations. A volatility distribution was derived to quantitatively describe the measured gas-particle partitioning data using absorptive partitioning theory. Although the POA emission factors varied by more than two orders of magnitude across the test fleet, the vehicle-to-vehicle differences in gas-particle partitioning were modest. Therefore, a single volatility distribution can be used to quantitatively describe the gas-particle partitioning of the entire test fleet. This distribution is designed to be applied to quartz filter POA emission factors in order to update emissions inventories for use in chemical transport models.

Characterization of Ultrafine Particulate Matter from Traditional and Improved Biomass Cookstoves

Biomass combustion in cookstoves has a substantial impact on human health, affects CO2 levels in the atmosphere, and black carbon (BC) and organic carbon (OC) affect the earth's radiative balance. Various initiatives propose to replace traditional fires with "improved" (nontraditional) cookstoves to offset negative local and global effects. In this laboratory study, we compared the size, composition, and morphology of ultrafine particulate emissions from a "three-stone" traditional fire to those from two improved stove designs (one "rocket", one "gasifier"). Measurement tools included a scanning mobility particle sizer, PTFE and quartz filter samples, and transmission electron microscopy. In the improved stoves, particulate mass (PM) emissions factors were much lower although median particle size was also lower: 35 and 24 nm for the rocket and gasifier, respectively, vs 61 nm for the three-stone fire. Particles from improved stoves formed clearly defined chain agglomerates and independent spheres with little evidence of volatile matter and had a higher proportion of BC to total PM, although overall BC emissions factors were fairly uniform. The 3-fold increase in quantities of sub-30 nm particles from improved cookstoves warrants further consideration by health scientists, with due consideration to the higher combustion efficiencies of improved cookstoves.

Determination of Volatility Distributions of Primary Organic Aerosol Emissions from Internal Combustion Engines Using Thermal Desorption Gas Chromatography Mass Spectrometry

A new technique for measuring the primary organic aerosol (POA) emissions from internal combustion engines is presented. The method combines thermal-optical OC/EC analysis and thermal desorption gas chromatography mass spectrometry (TD-GC-MS) of quartz filter samples collected using a dilution sampler to quantify the total emissions of low-volatility organics and to distribute them across the volatility basis set. These data can be used in conjunction with partitioning theory to predict the gas-particle partitioning and thus the total amount of POA over the entire range of atmospheric conditions. The approach is evaluated using POA emissions data from two gas-turbine engines and one diesel generator. To evaluate the new method, we directly measured the effects of temperature and concentration on gas-particle partitioning of the emissions from each. Predictions based on the volatility distributions derived from the filter analyses are consistent with the direct partitioning measurements. The new approach represents a major improvement over the traditional assumption of nonvolatile POA emissions, which over predicts actual POA emissions from these sources by a factor of 2–4 at typical ambient concentration and temperature. By using quartz filter samples, this new technique is designed to be applied to routine source test data. Volatility distributions derived using this new approach can also be applied directly to the large catalog of quartz filter data used by existing emission inventories and models. The emissions data derived from this approach are designed for use in the next generation of chemical transport models and emissions inventories that employ the volatility basis set approach to explicitly track the gas-particle partitioning of POA emissions. Copyright 2012 American Association for Aerosol Research

Determination of glyphosate through passive and active sampling methods in a treated field atmosphere

The study was carried out to determine the atmospheric residues of glyphosate (N-phosphonomethylglicine) using both passive and active sampling methods in Malaysia’s tropical weather conditions. The field was treated with Roundup (Monsanto) @ 2L ha-1 using Mistblower (Solo 412). Glyphosate was sampled in 12 h day time pre and post-spray sampling events using three simple and low-cost passive air samplers (cotton gauze, cellulose filter, and PUF) and active sampling using PUF plug and quartz filter cartridges. In pre-spray sampling event, no glyphosate detection was shown in both passive and active sampling. On the other hand, post-spray passive samples data revealed that only cotton gauze among the three passive air samples showed detection in both post-spray events during which the first post-spray (2.49 ng/cm2) showed significantly higher residue measurement than that of second post-spray period (0.84 ng/cm2). In active sampling, however, no glyphosate residue was detected in any of the PUF plug samples but detected only in quartz filter samples, revealing that glyphosate is associated with particles rather than vapour in the air. The highest concentration of glyphosate (42.96µg/m3) was measured in the air at operator’s breathing zoneduring the 25 min spray application period. In the post-spray active sampling periods, glyphosate residue was significantly far below compared to the spray period concentration. Furthermore, in paired comparison between active and passive sampling methods in terms of residue uptake performance, passive sampling showed significantly better performance than the active sampling method in this study. Key words: Glyphosate, active sampling, passive sampling, atmospheric residue.

Comparison of quartz and Teflon filters for simultaneous collection of size-separated ultrafine aerosol particles and gas-phase zero samples

In this research, the two most common filter media, quartz and Teflon, were tested to obtain information about the possible adsorption of gas-phase compounds onto filters during long sample collection of atmospheric aerosols. Particles of nanometer-size for off-line chemical characterization were collected using a recently introduced differential mobility analyzer for size separation. Samples were collected at an urban site (Helsinki, SMEARIII station) during spring 2010. Sampling time was 4 to 10 days for particles 50, 40, or 30 nm in diameter. Sample air flow was 4 L/min. The sampling setup was arranged so that two samples were obtained for each sampling period almost simultaneously: one containing particles and adsorbed gas-phase compounds and one containing adsorbed gas-phase compounds only. Filters were extracted and analyzed for the presence of selected carboxylic acids, polyols, nitrogen-containing compounds, and aldehydes. The results showed that, in quartz filter samples, gas-phase adsorption may be responsible for as much as 100% of some compound masses. Whether quartz or Teflon, simultaneous collection of gas-phase zero samples is essential during the whole sampling period. The dependence of the adsorption of gas-phase compounds on vapor pressure and the effect of adsorption on the deposited aerosol layer are discussed.

A new aerosol collector for quasi on-line analysis of particulate organic matter: the Aerosol Collection Module (ACM) and first applications with a GC/MS-FID

Abstract. In many environments organic matter significantly contributes to the composition of atmospheric aerosol particles influencing its properties. Detailed chemical characterization of ambient aerosols is critical in order to understand the formation process, composition, and properties of aerosols and facilitates source identification and relative contributions from different types of sources to ambient aerosols in the atmosphere. However, current analytical methods are far from full speciation of organic aerosols and often require sampling times of up to one week. Offline methods are also subjected to artifacts during aerosol collection and storage. In the present work a new technique for quasi on-line compound specific measurements of organic aerosol particles was developed. The Aerosol Collection Module (ACM) focuses particles into a beam which is directed to a cooled sampling surface. The sampling takes place in a high vacuum environment where the gas phase from the sample volume is removed. After collection is completed volatile and semi-volatile compounds are evaporated from the collection surface through heating and transferred to a detector. For laboratory characterization the ACM was interfaced with a Gas Chromatograph Mass Spectrometer, Flame Ionization Detector system (GC/MS-FID), abbreviated as ACM GC-MS. The particle collection efficiency, gas phase transfer efficiency, and linearity of the ACM GC-MS were determined using laboratory generated octadecane aerosols. The ACM GC-MS is linear over the investigated mass range of 10 to 100 ng and a recovery rate of 100% was found for octadecane particles. The ACM GC-MS was applied to investigate secondary organic aerosol (SOA) formed from β-pinene oxidation. Nopinone, myrtanal, myrtenol, 1-hydroxynopinone, 3-oxonopinone, 3,7-dihydroxynopinone, and bicyclo[3,1,1]hept-3-ene-2-one were found as products in the SOA. The ACM GC-MS results are compared to quartz filter samples taken in parallel to the ACM GC-MS measurements. First measurements of ambient atmospheric aerosols are presented.

A study of gas/particle partitioning of SVOCs in the tropical atmosphere of Southeast Asia

Gas- and particle-phase polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were collected at a tropical site in Southeast Asia over 12-h periods during November and December 2006 to determine their gas/particle distributions by analyzing integrated quartz filter and polyurethane foam samples. Gas/particle partitioning coefficients, K p, were calculated, and their relationship with the subcooled liquid vapor pressure p L o for both PAHs and PCBs was investigated. The regressions of log K p vs. log p L o for most of samples gave high correlations for both PAHs and PCBs and the slopes were statistically shallower than −1, but they were relatively steeper than those obtained in temperate zones of the Northern Hemisphere. By comparison, the particle-bound fraction of low molecular weight (LMW) PAHs was underestimated by both Junge-Pankow adsorption and K OA (octanol–air partition coefficient) absorption models, while the predicted values agree relatively better with those observed ones for high molecular weight (HMW) PAHs. In addition, the adsorption onto the soot phase (elemental carbon) predicted accurately the gas/particle partitioning of PAHs, especially for LMW compounds. On the other hand, the K OA absorption model using the measured organic matter fraction ( f OM) value fitted the PCB data much better than the adsorption model did, indicating the sorption of nonpolar compounds to aerosols might be dominated by absorption into organic matters in this area.

Two-Dimensional NMR Studies of Water-Soluble Organic Matter in Atmospheric Aerosols

The potential and the limitations of combining two-dimensional nuclear magnetic resonance (2D NMR) techniques to deliver new qualitative information on the substructures present in water-soluble organic compounds (WSOC) from fine atmospheric aerosols collected during Winter and Spring/Summer seasons are highlighted in this study. The WSOC fractions were extracted from quartz filter samples and further separated into hydrophobic acids and hydrophilic acids fractions by using a XAD-8/XAD-4 isolation procedure. Despite different spectral resolution, it was found that the aliphatic material of both samples includes mostly long-chain (carbons greater than 3 or 4) and branched mono- and dicarboxylic acids, carbonyl, and ester structural types. The presence of such structural fragments could be associated to secondary organic aerosol formation. It has been further demonstrated that spectral signatures typical of anhydrosugars from cellulose and methoxyphenols from lignin can be identified among the carbohydrate and aromatic moieties of the Winter sample. Their presence highlights the major influence of biomass burning on atmospheric particulate matter collected during colder periods. The data reported here demonstrate the success of 2D NMRtechniquesto investigate aerosol WSOC composition, as well as to evaluate aerosol source fingerprints.

Characterization of Water-Soluble Organic Carbon in Urban Atmospheric Aerosols Using Solid-State 13C NMR Spectroscopy

Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy has been used to investigate the distribution of carbon functional groups in urban Atlanta aerosol fine (PM2.5) particles. Carbonaceous aerosol particles comprise a significant fraction of the ambient particle mass and are environmentally significant as they may influence radiative and cloud-nucleating properties and can also produce adverse health effects upon inhalation. The water-soluble organic carbon (WSOC) fraction was extracted from multiple 24 h integrated high-volume quartz filter samples and further separated into recovered hydrophobic and hydrophilic fractions using an approach similar to that used to extract humic and fulvic acids from aqueous samples. Solid-state 13C NMR results indicate that WSOC in urban atmospheric aerosol particles is mostly aliphatic in nature (approximately 95% by C mass) with major contributions from alkyl and oxygenated alkyls (approximately 80%), carboxylic acid (approximately 10%), and aromatic functional groups (approximately 4%). The aromatic C is associated with the recovered hydrophobic fraction of WSOC. These spectra have been compared to the 13C NMR results obtained from Suwannee River humic acid and a fractionated biomass burning sample. WSOC, and more importantly, its recovered hydrophobic fraction, is found to be only qualitatively similar to aqueous humic material. The biomass burning sample is significantly different from urban Atlanta WSOC and is composed of substantial amounts of sugar derivatives and phenolic compounds, as expected. The NMR results demonstrate the potential of this technique to investigate aerosol WSOC composition and to study its variations with changes in parameters such aerosol sources.

Field validation of a semi-continuous method for aerosol black carbon (aethalometer) and temporal patterns of summertime hourly black carbon measurements in southwestern PA

Two methods for measuring aerosol elemental carbon (EC) are compared. Three-hour integrated carbon samples were collected on quartz filters during the summer of 1990 in Uniontown, PA, primarily during episodes of elevated particulate pollution levels. These samples were analyzed for EC and organic carbon (OC) using a thermo/optical reflectance (TOR) method. Aerosol black carbon (BC) was measured using an Aethalometer, a semi-continuous optical absorption method. The optical attenuation factor for ambient BC was supplied by the instrument manufacturer. Three-hour average concentrations were calculated from the semi-continuous BC measurements to temporally match the EC/OC integrated quartz filter samples. BC and EC concentrations are highly correlated over the study period ( R 2=0.925). The regression equation is BC (μg m -3)=0.95 (±0.04) EC−0.2 (±0.4). The means of 3 h average measurements for EC and BC are 2.3 and 2.0 μg m -3, respectively, average concentrations of EC and BC ranged from 0.6 to 9.4 and 0.5 to 9.0 μg m -3 respectively. TOR OC and EC concentrations were not highly correlated ( R 2=0.22). The mean OC/EC ratio was 1.85. The 10-week Aethalometer hourly dataset was analyzed for daily and weekly temporal patterns. A strong diurnal BC pattern was observed, with peaks occurring between 7 a.m. and 9 a.m. local time. This is consistent with the increase in emissions from ground level combustion sources in the morning, coupled with poor dispersion before daytime vertical mixing is established. There was also some indication of a day-of-week effect on BC concentrations, attributed to activity of local ground level anthropogenic sources. Comparison of BC concentrations with co-located measurements of coefficient of haze in a separate field study in Philadelphia, PA, during the summer of 1992 showed good correlation between the two measurements ( R 2=0.82).

The measurement of H 2SO 4 and other sulfate species at Tuxedo, New York with a thermal analysis flame photometric detector and simultaneously collected quartz filter samples

A study of major atmospheric particulate sulfate species was conducted during 30 July 1980–1983 September 1980 in Sterling Forest, a rural area in Tuxedo, NY, not affected by major local sources of pollution. In situ measurements of total sulfate, sulfuric acid and ammonium sulfate ammonium bisulfate were made using Thermal Analysis-Flame Photometric Detection (TA-FPD). These measurements were compared to the total sulfate and strong acid (H +) concentration measured in simultaneously collected 12 h, treated quartz filter samples. The concentration of NH 4HSO 4 was inferred from the difference between the total strong acid concentration and the sulfuric acid measurements, so that total sulfate and acid concentrations could be balanced. A major sulfate pollution episode occurred during the period of 27–29 August. The concentration of H + showed an excess above that necessary to account for the TA-FPD H 2SO 4 measurement, indicating the presence of NH 4 HSO 4. The maximum 12 h average concentrations of H 2SO 4, NH 4HSO 4 and (NH 4) 2SO 4 were 5.18, 11.42 and 10.08 μg m −3 as SO 4 2− respectively, and were measured from 9:15 to 21:15 on 28 August. The study demonstrated the usefulness of concurrent measurements of airborne particulate sulfate by filter extraction and TA-FPD to identify acidic sulfate species.