OC Ratios Research Articles

Characterization of primary and aged wood burning and coal combustion organic aerosols in an environmental chamber and its implications for atmospheric aerosols

Abstract. Particulate matter (PM) affects visibility, climate, and public health. Organic matter (OM), a uniquely complex portion of PM, can make up more than half of total atmospheric fine PM mass. We investigated the effect of aging on secondary organic aerosol (SOA) concentration and composition for wood burning (WB) and coal combustion (CC) emissions, two major atmospheric OM sources, using mid-infrared (MIR) spectroscopy and aerosol mass spectrometry (AMS). For this purpose, primary emissions were injected into an environmental chamber and aged using hydroxyl (diurnal aging) and nitrate (nocturnal aging) radicals to reach an atmospherically relevant oxidative age. A time-of-flight AMS instrument was used to measure the high-time-resolution composition of non-refractory fine PM, while fine PM was collected on PTFE filters before and after aging for MIR analysis. AMS and MIR spectroscopy indicate an approximately 3-fold enhancement of organic aerosol (OA) concentration after aging (not wall-loss corrected). The OM:OC ratios also agree closely between the two methods and increase, on average, from 1.6 before aging to 2 during the course of aging. MIR spectroscopy, which is able to differentiate among oxygenated groups, shows a distinct functional group composition for aged WB (high abundance of carboxylic acids) and CC OA (high abundance of non-acid carbonyls) and detects aromatics and polycyclic aromatic hydrocarbons (PAHs) in emissions of both sources. The MIR spectra of fresh WB and CC aerosols are reminiscent of their parent compounds with differences in specific oxygenated functional groups after aging, consistent with expected oxidation pathways for volatile organic compounds (VOCs) of each emission source. The AMS mass spectra also show variations due to source and aging that are consistent with the MIR functional group (FG) analysis. Finally, a comparison of the MIR spectra of aged chamber WB OA with that of ambient samples affected by residential wood burning and wildfires reveals similarities regarding the high abundance of organics, especially acids, and the visible signatures of lignin and levoglucosan. This finding is beneficial for the source identification of atmospheric aerosols and interpretation of their complex MIR spectra.

Analysis of functional groups in atmospheric aerosols by infrared spectroscopy: method development for probabilistic modeling of organic carbon and organic matter concentrations

Abstract. The Fourier transform infrared (FTIR) spectra of fine particulate matter (PM2.5) contain many important absorption bands relevant for characterizing organic matter (OM) and obtaining organic matter to organic carbon (OM∕OC) ratios. However, extracting this information quantitatively – accounting for overlapping absorption bands and relating absorption to molar abundance – and furthermore relating abundances of functional groups to that of carbon atoms poses several challenges. In this work, we define a set of parameters that model these relationships and apply a probabilistic framework to identify values consistent with collocated field measurements of thermal–optical reflectance organic carbon (TOR OC). Parameter values are characterized for various sample types identified by cluster analysis of sample FTIR spectra, which are available for 17 sites in the Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring network (7 sites in 2011 and 10 additional sites in 2013). The cluster analysis appears to separate samples according to predominant influence by dust, residential wood burning, wildfire, urban sources, and biogenic aerosols. Functional groups calibrations of aliphatic CH, alcohol COH, carboxylic acid COOH, carboxylate COO, and amine NH2 combined together reproduce TOR OC concentrations with reasonable agreement (r=0.96 for 2474 samples) and provide OM∕OC values generally consistent with our current best estimate of ambient OC. The mean OM∕OC ratios corresponding to sample types determined from cluster analysis range between 1.4 and 2.0, though ratios for individual samples exhibit a larger range. Trends in OM∕OC for sites aggregated by region or year are compared with another regression approach for estimating OM∕OC ratios from a mass closure equation of the major chemical species contributing to PM fine mass. Differences in OM∕OC estimates are observed according to estimation method and are explained through the sample types determined from spectral profiles of the PM.

The robustness of single-point Tenax extractions of pyrethroids: Effects of the Tenax to organic carbon mass ratio on exposure estimates

Use of Tenax extractable concentrations to estimate biological exposure to hydrophobic organic contaminants is well documented, yet method variation exists between studies, specifically in the ratio of Tenax mass to organic carbon mass in the sediment (Tenax:OC ratio) being extracted. The effects of this variation on exposure estimates are not well understood. As Tenax is theoretically in direct competition with organic carbon for freely dissolved chemical in sediment interstitial water, varying the Tenax:OC ratio could impact single-point Tenax extraction (SPTE) exposure estimates. Therefore, the effects of varying Tenax:OC ratios on SPTE pyrethroid concentrations from field-contaminated and laboratory-spiked sediments were compared to bioaccumulation by Lumbriculus variegatus. The Tenax:OC ratio had minimal effect on SPTE pyrethroid concentrations. The SPTE pyrethroid concentrations obtained using the highest and lowest Tenax:OC ratios ranged from 0.85- to 3.91-fold different, which is unlikely to contribute substantial error to bioaccessibility estimates. Comparisons to Tenax exposure endpoints from previous research reveal the variation in these endpoints is likely due to toxicokinetic and toxicodynamic differences; processes common to exposure estimates provided by any chemical extraction technique. As the pyrethroid concentrations in the experimental sediments caused toxicity to L. variegatus, thus affecting bioaccumulation, the SPTE concentrations overestimated bioaccumulation. However, SPTE concentrations strongly correlated with growth inhibition regardless of the Tenax:OC ratio, providing accurate estimates of the correct exposure endpoint. Tenax masses of 0.500–0.800 g should provide sufficient Tenax to achieve Tenax:OC ratios of at least 5:1, which will provide accurate exposure estimates while retaining the ease of conducting SPTEs.

Relationship between carbonaceous components and aerosol light absorption during winter at an urban site of Gwangju, Korea

To examine the relationship between the chemical composition of light-absorbing organic aerosols and the absorption properties of the aerosols, daily PM2.5 samples were collected during winter at an urban site of Gwangju, Korea, and analyzed for organic carbon and elemental carbon (OC and EC), water-soluble organic carbon (WSOC), humic-like substances (HULIS), and water-soluble inorganic substances. The real-time black carbon (BC) concentration in PM2.5 was also measured using a dual-spot aethalometer. During the study period, average WSOC/OC and HULIS-C/WSOC ratios were 0.53 and 0.52, respectively. K+/EC and K+/OC ratios indicate that biomass burning (BB) emissions are a possible source of the observed carbonaceous aerosols and K+. Moderate-to-strong correlations of HULIS with NO3−, oxalate, SO42−, K+, CO, and ΔBC (=BC@370nm−BC@880nm) suggest that in addition to the primary BB emissions, secondary processing is another important contributor to the formation of HULIS in winter at the site.The average absorption Ångstrӧm exponent (α) of fine aerosols for the wavelengths of 370–950nm and 590–950nm was 1.29 and 1.18, respectively, but the aerosol α value was higher in the near UV wavelength range (370–520nm), with an average of 1.51 (0.76–2.36), indicating that aerosol absorption characteristics during winter were influenced by BB aerosol sources, as well as by traffic emissions. Over the study period, the α370–520nm value during the highest EC, highest OC, and Asian dust events was 1.42±0.10 (1.26–1.59), 1.44±0.15 (1.16–1.68), and 1.90±0.28 (1.54–2.36), respectively. Higher α370–520nm values during the Asian dust event were attributed to the influence of dust particles. In addition, the light absorption coefficients of aerosols at 370nm were strongly correlated with OC (R2=0.76), water-insoluble OC (R2=0.70), and water-soluble HULIS (R2=0.64). These tight correlations suggest that water-insoluble fractions of OC, as well as the water-soluble brown carbon, could be important contributors to aerosol light absorption. This study demonstrates that a newly-developed dual-spot aethalometer could be utilized to characterize light absorption properties of organic aerosols and dust particles.

Biomass burning contributions to urban PM2.5 along the coastal lines of southeastern China

Levoglucosan (LG), water soluble organic carbon (WSOC) and potassium (K+), and the light absorption at 365 nm (Abs365) of the extracted WSOC are measured in PM2.5 samples collected from November 2011 to July 2013 at four coastal urban sites in southeast China (Fuzhou, Putian, Quanzhou and Xiamen). These species are markers of biomass burning and used to determine the contributions of biomass burning to the PM2.5 burden in these locations. LG and WSOC concentrations exhibited a clear seasonal pattern, with a large enhancement in winter and spring and a minimum in summer, and annual means across all sites of 59.2±46.8 ng m−3 and 2.69±1.21 µg C m−3, respectively. The distinctive seasonal patterns of LG and WSOC are more explained by the East Asian monsoon than the upwind varying emission sources according to the HYSPLIT backward trajectories and MODIS fire spots. Observations produced significant correlation (at the p<0.01 level) between LG and non-sea salt K+ (nss-K+) at each site, but the correlations exhibited no clear seasonal trend. The LG/nss-K+ ratios ranged from 0.03±0.01 to 0.24±0.13 which lay within the limits for the crop residues and/or grass combustion smoke. Stronger correlations were found between WSOC or Abs365 and sulphate than between WSOC and LG. This observation is consistent with the fact that biomass burning is a less important contributor to WSOC and/or brown carbon than is secondary organic aerosol formation and oxidation. The average relative contributions of biomass burning to OC and WSOC in PM2.5 were 8.3 and 15.2 %, respectively, estimated by the measured LG to OC and WSOC (LG/OC and LG/WSOC) ratios in comparison to literature-derived LG/OC and LG/WSOC values for biomass burning smoke. Using the reported conversion factor of LG to PM2.5 for crop straw burning smoke, the LG-estimated PM2.5 contributions from biomass burning exhibited minimum values in summer and higher values in winter and spring. Positive Matrix Factorisation was used to analyse PM2.5 sources, and seven major source factors including biomass burning emissions were resolved. The biomass burning sources contributed 3.75–8.08 % to PM2.5 mass as an annual average while exhibiting a seasonal variability similar to and higher than those of LG-estimated contributions. These results demonstrate that the contribution from biomass burning smoke to PM2.5 – while small – is non-negligible, especially in the winter and spring sampling periods, that is, northeastern monsoon season.

Chemical composition of PM2.5 at a high–altitude regional background site over Northeast of Tibet Plateau

Aerosol samples were collected from a site near Qinghai Lake (QHL) on the northeastern margin of the Tibetan Plateau (TP) to investigate PM2.5 mass levels and chemical composition, especially their seasonal patterns and sources. The PM2.5 ranged from 5.7 to 149.7μg m–3, and it was predominately crustal material (-40% on average). The combined mass of eight water–soluble inorganic ions ranged from 1.0 to 41.5μg m–3, with the largest contributions from SO42– NO3-, and Ca2+. Low abundances of organic carbon (OC, range: 1.0 to 8.2μg m–3) and elemental carbon (EC, 0.2 to 2.3μg m–3) were found in QHL. Weak seasonality in the OC/EC ratio (4.5±2.0) indicated simple and stable sources for carbonaceous particles. The water–soluble ions, OC and EC accounted for ~30%, 10% and 2% of the PM2.5, respectively. Water–soluble organic carbon (WSOC, range: 0.5 to 4.3μg m–3) accounted for 47.8% of the OC. Both OC and WSOC were positively correlated with water–soluble K+(r=0.70 and 0.73 respectively), an indicator of biomass burning. Higher WSOC and stronger correlations between WSOC and EC in spring and winter compared with summer and autumn are evidence for primary biomass burning aerosols. The concentrations of mass and major compositions were 2–10 times higher than those for some TP or continental background sites but much lower than urban areas. Compared with particles produced from burning yak dung (a presumptive source material), PM2.5 had higher SO42–/OC ratios. The higher ratios were presumed as a result of fossil fuel combustion. After excluding data for dust storms events, the relative percentages of OM, EC, K+, NH4+, NO3– and mineral dust showed little difference among seasons despite different monsoons dominated in four seasons; implying that the PM2.5 sources were relatively stable. The results from QHL evidently reflect regional cha racteristics of the aerosol.

A yearlong study of water-soluble organic carbon in Beijing I: Sources and its primary vs. secondary nature

Sources and properties of water-soluble organic carbon (WSOC) were investigated based on fine particulate matter (PM2.5) samples collected in Beijing during a thirteen month campaign. The WSOC to OC ratios averaged 45.9% annually and were substantially higher in summer compared with the other seasons. WSOC exhibited strong correlation with secondary components such as secondary organic aerosol estimated by the elemental carbon (EC)-tracer method and inorganic ions (e.g., sulfate and nitrate), whereas the correlation between WSOC and EC was much weaker, suggesting that WSOC should be dominated by secondary species. Moreover, the trend of the WSOC to EC ratio was found to coincide with that of relative humidity during winter, spring and fall. High WSOC/EC ratio in February indicates high humidity could enhance the formation potential of WSOC in winter. Sources of WSOC were further investigated by a receptor model (Positive Matrix Factorization model). The apportionment results suggested that biomass burning contributed about 40% of WSOC while about 54% of WSOC was associated with oxalate and sulfate, whereas a primary factor was responsible for only 6% of WSOC also demonstrating that primary emissions are not the main source of WSOC.

Emission factors and detailed chemical composition of smoke particles from the 2010 wildfire season

This paper complements the information previously published (Atmospheric Environment 45, 641–649) on gaseous and particulate emissions from wildfires in Portugal for summer 2009, in an attempt at obtaining more extensive, complete and representative databases on emission factors and detailed chemical characterisation of smoke particles. Here, emission factors for carbon oxides (CO2 and CO), total hydrocarbons (THC), fine (PM2.5) and coarse (PM2.5–10) particles obtained for fires occurring in Portugal in summer 2010 are presented. The carbonaceous content (OC and EC), water-soluble ions, elements and organic composition of smoke particles were, respectively, analysed by a thermal-optical transmission technique, ion chromatography, instrumental neutron activation analysis (INAA) and gas chromatography-mass spectrometry (GC–MS). The particle mass concentrations were in the ranges 0.69–25 mg m−3 for PM2.5 and 0.048–3.1 mg m−3 for PM2.5–10. PM2.5 particles represented 91 ± 5.7% of the PM10 mass. The OC/EC ratios in fine and coarse particles ranged from 2.5 to 205 and from 1.7 to 328, respectively. The water-soluble ions represented, on average, 3.9% and 2.8% of PM2.5 and PM2.5–10 mass, respectively. In general, the dominant ions in the water extracts were Na+, NH4+, Cl− and NO3− for the PM2.5 fraction, and K+, Mg2+, Ca2+ and SO42− for the PM2.5–10 fraction. The K+/EC and K+/OC ratios obtained in this study were, on average, 0.22 ± 0.23 and 0.011 ± 0.014 for PM2.5 and 0.83 ± 1.0 and 0.024 ± 0.023 for PM2.5–10 particles, respectively. The K+/levoglucosan ratio was, on average, 2.0 for PM2.5 and 3.1 for PM2.5−10 particles. Levoglucosan was detected at mass fractions of 1.6–8.7 mg g−1 OC in PM2.5 and 2.7–56 mg g−1 OC in PM2.5–10. The dominant elements detected in the smoke samples were Na, Br, Cr, Fe, K, Rb and Zn. The most representative organic constituents in the smoke samples were acids, alcohols, terpenoid-type compounds, sugars and phenols, in both size fractions.

Regional modeling of secondary organic aerosol over China using WRF/Chem

Using a new generation air quality modeling system (WRF/Chem) fully coupled with secondary organic aerosol model (SORGAM), we investigate the spatial and temporal characteristics of secondary organic aerosol (SOA) as well as the relative contributions of anthropogenic and biogenic sources to the formation of SOA in 2006 over China. To improve SOA simulation, a parameterization scheme for the isoprene induced SOA formation was added in WRF/Chem. The simulated SOA concentrations show large temporal and spatial variability, with the highest levels occur in summer and the lowest concentrations occur in winter. The high SOA regions are located near 30°N in central China in summer, with values exceeding 8 μg m −3, while they shift to South China, mainly in Pearl River Delta (PRD) region in winter, with the concentrations at or below 2 μg m −3. Across the whole country, the average ground level SOA concentrations are 0.94, 2.54, 1.41, 0.43, and 1.34 μg m −3 in spring, summer, autumn, winter, and year, respectively. Commonly, the SOA loading is mostly concentrated in the boundary layer (∼70%). Although the SOA concentrations are dominated by biogenic sources in summer, the contributions of anthropogenic sources exceed biogenic sources over most areas in winter. On the national level, the anthropogenic sources contribute 35% of total SOA, with 41%, 26%, 39%, and 59% in spring, summer, autumn and winter, respectively. The estimated annual SOA production reaches 3.05 Tg yr −1 over China, accounting for about 4–25% of global SOA formation. The modeled OC and EC concentrations as well as SOC to OC ratios are compared with the measurements and previous studies. The results suggest that the spatial and temporal characteristic of OC and EC levels is well captured by the model. However, the simulated SOA concentrations in this study might be underestimated by 0–75%. The modeling SOA in this paper are in agreement with other field and modeling studies, also showing the importance of SOA in total organic aerosol in China.

Photochemical changes in chemical markers of sedimentary organic matter source and age

Several chemical markers of organic matter source and age are shown to be susceptible to light-induced alteration. To test for the photochemical lability of markers previously employed for sediments from the Louisiana coastal zone, we subjected sediments under resuspension conditions to simulated sunlight, and monitored changes in C:N and Br:OC ratios, δ 13C, Δ 14C, and lignin composition. Markers of terrigenous origin (high C:N, lignin) decreased and δ 13C became enriched in sediments containing primarily terrigenous organic matter, while a marker of marine organic matter (Br:OC) decreased in samples containing significant contributions from this source. Preferential loss of 14C from all sediments indicated enhanced photochemical lability of organic matter of relatively recent origin, consistent with the changes in chemical markers. Most, but not all, experimental alterations are consistent with field distributions of these markers. Relatively small experimental changes in the markers in combination with confounding processes in the environment, however, prevent these parallel trends from providing any more than a consistency test for the importance of photochemical reactions in this region.

Oxidation State and Size of Fe Controlled by Organic Matter in Natural Waters

In a well mixed-stream, in which the iron/organic carbon (OC) ratio varied from 0.333 to 0.05 with sampling point and discharge, 40-70% of the Fe load was found to be present as lightly bound Fe(II). In laboratory simulations of streamwater, after 24 h of aeration at pH 6.5, and with an Fe/OC concentration ratio of 0.417, 97% of Fe(II) was converted to Fe(III) (hydr)oxides, while at a ratio of 0.083, 87% of Fe(ll) remained unoxidized. The particle size distribution of Fe contained < 0.2 microm fractions only when OC was present and comparison of Fe and OC size distributions suggested that there was more than one mechanism by which colloidal Fe was produced. At high Fe/ OC ratios, < 0.2 microm fractions may be predominantly Fe(III) (hydr)oxides stabilized by OC, but at low ratios, they must consist of otherwise soluble Fe(ll) attached to < 0.2 microm OC. The recognition in the field of the consequences of processes demonstrated in the laboratory suggests that OC may be a predominant control of both size and oxidation state of Fe in many natural waters.

Marine vs. terrigenous organic matter in Louisiana coastal sediments: The uses of bromine:organic carbon ratios

Recent data on the sources of organic carbon buried in the ocean have emphasized the probable importance of terrigenous organic matter in burial budgets of deltaic depocenters. The many markers used to assess relative importance of marine vs. terrestrial sources each have ambiguities. We use the ratio of bromine to organic carbon (Br:OC) as a source indicator for organic matter in the Mississippi delta. Progressive increases in bromine concentrations from the river to the slope indicate increasing content of marine-derived organic matter. Quantitative estimates of marine vs. terrigenous organic matter using Br:OC ratios in a two-endmember mixing model are consistent with recent estimates using a combination of three other source markers [Gordon, E.S., Goñi, M.A. 2003. Sources and distribution of terrigenous organic matter delivered by the Atchafalaya River to sediments in the northern Gulf of Mexico. Geochim. Cosmochim. Acta, 67:2359–2375]. The Br:OC vs. δ 13C relationship indicates seaward increase in δ 13C without proportionate incorporation of marine organic matter, consistent with recent arguments that isotopically depleted terrestrial detritus derived from C3 plants is separated from C4-derived terrigenous organic matter during transport. Decreasing Br:OC ratios downcore at many sites that have significant amounts of marine organic matter indicate that the marine organic matter is preferentially lost during burial diagenesis. This preferential loss constrains the contribution of organic matter burial in deltaic environments to global removal of Br.

Seasonal abundance of organic molecular markers in urban particulate matter from Philadelphia, PA

Organic molecular markers were measured in airborne particulate matter (PM10) from the City of Philadelphia North Broad Street air quality monitoring site to identify the seasonal abundance of key tracer compounds together with their dominant sources. Daily PM10 samples were collected seasonally in 2000 for four 2-week periods (January, April, August, and October). The North Broad Street site is within a heavily populated location in Philadelphia, PA. A suite of 52 individual organic marker compounds was monitored in the PM10 samples. Molecular markers, homologous compound series, and nonpolar and polar organic compounds were detected at ng m −3 ambient concentrations using gas chromatography/ion trap mass spectrometry (GC/IT MS). Organic diacids (C 3–C 9) and monoacids (C 10–C 30) had seasonal mass concentrations ranging from 91.0 (winter) to 261.8 ng m −3 (summer). Total n-alkanes (C 25–C 33) ranged from 25.9 (spring) to 49.5 ng m −3 (fall), total PAHs from 2.1 ng m −3 (summer) to 4.1 ng m −3 (winter), and total hopanes ranged from 4.0 ng m −3 (winter) to 7.4 ng m −3 (fall). The molecular marker ambient mass concentrations were normalized by the annual average mass of PM10 elemental carbon (EC) for the central Philadelphia area. The ambient mass concentrations to EC and OC ratios ranged from 2.6×10 −3 for total PAHs to EC to 115.3×10 −3 for total n-alkanoic acids to EC, 0.5×10 −3 for total PAHs to OC to 23.8×10 −3 for total n-alkanoic acids to OC. Ambient concentrations of individual markers are similar to other reported levels for metropolitan Los Angeles, CA and Atlanta, GA. Seasonal and daily variations of marker compounds are consistent with motor vehicle exhaust, particularly in winter. Summer concentration patterns indicate the importance of secondary organic aerosol to the PM10 ambient mass.

Some electrical circuit properties of the organ of Corti. II. Analysis including reactive elements

The simplified network model of the organ of Corti-hair cell complex that was studied in previous publications (Dallos P. (1983): In: Hearing — Physiological Bases and Biophysics, pp. 32–37, editors: R. Klinke and R. Hartmann; Dallos P. (1983): Hearing Res. 12, 89–119) is extended to include the capacitive reactances of hair cell membranes. With the assumption that the circuit is parametrically excited by resistance changes of the apical hair cell membrane, intracellular responses for outer ( e O ) and inner ( e I ) hair cells and the organ of Corti potential ( OC ) computed for the linear case. In order that frequency-dependent effects be primarily determined by the network properties of the system, the e O e OC and e I e OC ratios are considered. The amplitude and phase dependence of these computed functions is compared to corresponding experimental results from the third turn of the guinea pig's cochlea. The e o e OC function is predicted to be a simple low-pass filter whose cutoff frequency (1250 Hz) is determined by the parallel resistance-capacitance circuit of the cell's baso-lateral membrane. This circuit prediction is in excellent agreement with the data. The e I e OC function is again derived as a low-pass filter. The cutoff frequency is obtained as 472 Hz, which corresponds to an RC membrane time constant of 0.34 ms. Experimental data are widely divergent from this predicted pattern. In order to bring the theoretical and experimental results in agreement, two steps are necessary. First, a differentiation (i.e., multiplication by jω) needs to be included in the input to inner hair cells to account for their velocity dependence [4,10]. Second, an underdamped complex pole, located above the cell's best frequency must be introduced. The velocity dependence and the resonance represented by the underdamped pole-pair indicate that the electrical response pattern of inner hair cells is more complex than that of outer hair cells.

The distribution of bromine in coastal sediments and its use as a source indicator for organic matter

The distribution of bromine associated with sedimentary organic matter (SOM) was examined in the Gulf of Maine and two contiguous estuaries. The bromine to organic carbon (Br:OC) ratio is constant throughout the Gulf of Maine but shows considerable variability in the estuarine regions. These variations seem to reflect the bromine contents of the various primary productivity sources of the SOM. Decreasing Br:OC ratios correlate with decreasing δ 13C values in a suite of estaurine sediments containing varying proportions of marine-derived and terrigenous SOM. High Br:OC ratios appear to represent macroalgal contributions to SOM. While both Br and OC levels are dependent upon sediment texture, their ratio is not. Br:OC ratios in SOM are higher than those of its primary productivity sources, which may result from residual enrichment of brominated organic material during decay rather than uptake of Br − by SOM.