Min-Suk Bae

Sampling methods used for the collection of particle-phase organic and elemental carbon during ACE-Asia

Abstract The semi-volatile nature of carbonaceous aerosols complicates their collection, and for this reason special air sampling configurations must be utilized. ACE-Asia provided a unique opportunity to compare different sampling techniques for collecting carbonaceous aerosols. In this paper detailed comparisons between filter-based carbonaceous aerosol sampling methods are made. The majority of organic carbon (OC) present on a backup quartz fiber filter (QFF) in an undenuded-filter sampler resulted from the adsorption of native gaseous OC rather than OC evaporated from collected particles. The level of OC on a backup QFF placed behind a QFF was lower than the level present on a backup QFF placed behind a Teflon membrane filter (TMF) indicating that gas/filter equilibrium may not be achieved in some QFF front and backup filter pairs. Gas adsorption artifacts can result in a 20–100% overestimation of the ambient particle-phase OC concentration. The gas collection efficiency of XAD-coated and carbon-impregnated filter-lined denuders were not always 100%, but, nonetheless, such denuders minimize gas adsorption artifacts. The median fraction of particle-phase OC that is estimated to evaporate from particles collected by denuder-filter samplers ranged from 0 to 0.2; this value depends on the sampler configuration, chemical composition of the OC, and sampling conditions. After properly correcting for sampling artifacts, the measured OC concentration may differ by 10% between undenuded- and denuder-filter samplers. Uncorrected, such differences can be as large as a factor two, illustrating the importance of sampling configurations in which gas adsorption or evaporation artifacts are reduced or can be corrected.

Hourly and Daily Patterns of Particle-Phase Organic and Elemental Carbon Concentrations in the Urban Atmosphere

Abstract Two semicontinuous elemental and organic carbon analyzers along with daily integrated samplers, which were used for laboratory elemental and organic carbon analysis, were operated to measure PM2.5 organic carbon (OC) and elemental carbon (EC) for the entire year of 2002 at the St. Louis Midwest Supersite. The annual-average denuded OC and EC concentrations were 3.88 and 0.7 μg/m3, respectively. A comparison of the 24-hr average denuded and undenuded OC measurements showed a positive bias for the undenuded OC measurement that was best represented by a positive intercept of 0.34 ± 0.1 μg/m3 and a slope of 1.06 ± 0.02, with an R2 of 0.91. The full year of daily EC and OC measurements was used to demonstrate that a one-in-six-day sampling strategy at this site accurately represents the annual average concentrations. Although fine particle OC concentrations did not correlate with day of the week, EC concentrations showed a significant weekly pattern, with the highest concentration during the middle of the workweek and the lowest concentration on Sundays. Hourly EC and OC measurements yielded average diurnal patterns for the EC to OC ratio that peaked during morning rush hour traffic on weekdays but not on weekends.

Estimation of the Monthly Average Ratios of Organic Mass to Organic Carbon for Fine Particulate Matter at an Urban Site

Two independent methods are used to estimate the seasonality of the ratio of fine particulate organic matter (OM) to fine particulate organic carbon (OC) for atmospheric particulate matter collected at the St. Louis—Midwest Supersite. The first method assumes that all of the fine particulate matter mass that cannot be attributed to sulfate ion, nitrate ion, ammonium ion, elemental carbon and metal oxides is organic matter. Using this method, 98 daily samples were used to estimate the annual average fine particulate matter OM/OC ratio to be 1.81 ± 0.07 with a summer average of 1.95 ± 0.17 and a winter average of 1.77 ± 0.13. The second approach to estimating fine particle OM/OC employed OC source apportionment results and estimates of source specific OM/OC, including primary sources and secondary organic aerosol. The OM/OC estimate that was based on 98 daily source apportionment calculations over a two year period yielded an annual average ratio of 1.96 ± 0.03. Methods used in the study yielded a relatively stable annual average estimate of the OM/OC ratio for fine particulate matter in the St. Louis area. The source apportionment results indicate that the similar OM/OC ratio for St. Louis in the summer and winter results from an increased relative contribution of secondary organic aerosol in the summer months that is balanced by the higher woodsmoke in the winter. Although the estimated OM/OC ratios that were determined for St. Louis cannot be directly applied to other locations, the methodologies used to estimate OM/OC can be broadly applied given the necessary data for these calculations.

Effect of Engine Operating Conditions on Particle-Phase Organic Compounds in Engine Exhaust of a Heavy-Duty Direct-Injection (D.I.) Diesel Engine

Significant amounts of particle-phase organic compounds are present in the exhaust of diesel vehicles. It is believed that some of these compounds have a greater impact on human health and the environment than other compounds. Therefore, it is of significant importance to speciate particle-phase organic compounds of diesel particulate matter (PM) to clarify the effects of PM on human health and the environment, and to understand the mechanisms of organic compounds formation in PM. A dilution source sampling system was incorporated into the exhaust measurement system of a single-cylinder heavy-duty direct-injection (D.I.) diesel engine. This system was designed specifically to collect fine organic aerosols from diesel exhaust. The detailed system is described in Kweon et al. [27]. Samples were collected on a series of quartz fiber filters and analyzed by gas chromatography/mass spectrometry (GC/MS) techniques to quantify particle-phase organic compounds for various engine-operating conditions. The Cummins N14-series single-cylinder research engine was run under the California Air Resources Board (CARB) 8-mode test cycle. Thirty nine particle-phase organic compounds were quantified with high resolution particularly for light and medium load conditions. At the high load conditions, most of the particle-phase organic compounds were below detection limit of the GC/MS. Results show that detailed organic chemical composition of PM is significantly affected by the change in the engine load and speed. Most of the organic compounds were observed at idling, light, and medium load conditions. The n-alkanes and PAHs comprised between 68 and 83% of the total identified particle-phase organic compounds with the n-alkanes between 39 and 44% and the PAHs between 28.5 and 39.3% for the conditions except the mode 2, in which the concentrations of the particle-phase organic compounds were above detection limits. The hydrocarbon distribution shows that the fractions of carbon numbers in PM varied significantly, particularly those with carbon numbers below 20 and between 25 and 30. Carbon numbers between 25 and 30 comprised a significant portion in the hydrocarbon distributions at light load and idling conditions. However, the fraction of the carbon number of less than 20 increased tremendously at higher loads. Carbon numbers of larger than 30 remained without significant change.

Daily Variation in Particle-Phase Source Tracers in an Urban Atmosphere

One full year of daily 24-hour fine particulate matter samples collected in East St. Louis, IL at the EPA funded St. Louis-Midwest Supersite were analyzed for organic carbon (OC), elemental carbon (EC) and non-polar organic tracers including polycyclic aromatic hydrocarbons (PAH(s)), hopanes, and alkanes. Two different analytical methods were used for analysis, solvent extraction gas chromatography/mass spectrometry (GCMS) and thermal desorption GCMS (TD-GCMS). The TD-GCMS method was equivalent to the solvent extraction GCMS method for key molecular markers. Select PAH(s) and alkanes were found to have extreme events within the annual study which had daily 24-hour concentrations that were 10 to 22 times higher than the annual average daily concentration. The OC and EC maxima were only 3 to 5 times higher than the annual average. To further assess the impact of point sources and to evaluate the compatibility of the two organic speciation methods, the six potential every sixth day annual averages were calculated and compared. The extreme concentration days were large enough, in the case of benzo[a]pyrene, to make every sixth day analysis not representative of the true annual average even with events greater than the 99th percentile of the annual distribution removed. The final analysis calculated day of the week averages for select representative organic tracers and revealed that gasoline motor vehicle tracers and OC do not have a distinct day of the week trend. EC, believed to be largely impacted by diesel exhaust, had a midweek concentration peak. These trends cannot necessarily be extrapolated to other urban areas or other events.

Source identification of water-soluble organic aerosols at a roadway site using a positive matrix factorization analysis.

Daily PM2.5 measurements were carried out at a local roadway every sixth day from May 2011 to August 2013 to obtain seasonal quantitative information on the primary and secondary sources of two water-soluble organic carbon (WSOC) fractions. Filter samples were analyzed for OC, elemental carbon (EC), WSOC, hydrophilic and hydrophobic WSOC fractions (WSOC(HPI) and WSOC(HPO)), and ionic species. An XAD solid phase extraction method and a total organic carbon analyzer were used to isolate the two WSOC fractions and determine their amounts, respectively. The WSOC/OC and WSOC(HPI)/WSOC ratios were 0.62±0.13 and 0.47±0.14, respectively. Similar seasonal profiles in EC, OC, and WSOC concentrations were observed, with higher concentrations occurring in the cold season and lower concentrations in the warm season. However, opposite results were obtained in WSOC/OC and WSOC(HPI)/WSOC ratios, with the higher in the warm season and the lower in the cold season. Correlation analyses indicated that two WSOC fractions in winter were likely attributed to secondary formation processes, biomass burning (BB), and traffic emissions, while WSOC(HPI) observed in other seasons were associated with secondary formation processes similar to those of oxalate and secondary inorganic species. A positive matrix factorization (PMF) model was employed to investigate the sources of two WSOC fractions. PMF indicated that concentrations of WSOC fractions were affected by five sources: secondary NO3(-) related, secondary SO4(2-) and oxalate related, traffic emissions, BB emissions, and sea-salt. Throughout the study period, secondary organic aerosols were estimated to be the most dominant contributor of WSOC fractions, with higher contributions occurring in the warm seasons. The contribution of secondary aerosol formation processes (NO3(-) related+SO4(2-) and oxalate related) to WSOC(HPI) and WSOC(HPO) was on an average 56.2% (45.0-73.8%) and 47.7% (39.6-52.1%), respectively. The seasonal average contribution of WSOC(HPI) and WSOC(HPO) attributed to BB was 19.0% (14.3-25.3%) and 14.8% (7.2-19.5%), respectively, with higher fractions occurring in the fall and winter. Traffic sources contributed to WSOC(HPI) and WSOC(HPO) from 4.2 to 21.0% (an average of 11.6%) and from 7.9 to 32.3% (an average of 19.9%), respectively, with higher fractions in the fall and winter compared with the other seasons. During the study period, for an episode associated with high local O3 level (~110 ppbv) and high WSOC(HPI)/WSOC (0.80), secondary formation processes contributed 67.1% to WSOCHPI, and 72.6% to WSOC(HPO), respectively. However, for an episode associated with local and severe regional haze pollutions, contributions of secondary formation processes to WSOC fractions were observed to be low (32.4-43.1%), while traffic and BB emissions contributed 16.8% and 24.3% to WSOC(HPI), respectively, and 18.3% and 18.7% to WSOC(HPO), respectively. The PMF results suggest that the contribution of traffic emissions to concentrations of two WSOC fractions cannot be neglected at the studied roadway site.

Seasonal variations of elemental carbon in urban aerosols as measured by two common thermal-optical carbon methods.

Two commonly employed laboratory-based elemental carbon (EC) and organic carbon (OC) thermal/optical methods for the analysis of ambient particulate matter were used to analyze 709 twenty-four hour integrated PM(2.5) samples along with 76 field blanks from the St. Louis-Midwest Supersite in East St. Louis, Illinois. The two laboratory ECOC methods were the Aerosol Characterization Experiment-Asia (ACE-Asia) method based on National Institute of Occupational Safety and Health (NIOSH 5040) method and the Interagency Monitoring of Protected Visual Environments (IMPROVE) protocol. As in previous intercomparisons between these two methods, there was excellent agreement for total carbon (i.e. sum of EC and OC), but significant differences were observed in the split between the measured EC and OC. The 709 daily PM(2.5) samples spanned a time series of two years that allowed an assessment of seasonal relationships between the EC reported by the two methods. Seasonal average ACE-Asia and IMPROVE EC concentration values were highest in the fall and lowest in the spring. Differences between the seasonal average IMPROVE and ACE-Asia EC concentration values were about 40% greater in summer compared to winter. While IMPROVE EC values were always larger than ACE-Asia EC, the EC difference between these methods exhibited a strong seasonal variation with largest differences occurring in the spring and especially summer with the smallest differences in the fall and winter. Seasonal average EC differences (IMPROVE-ACE-Asia) were anti-correlated with molecular markers for biomass burning and mobile source emissions that had wintertime maximum concentrations. The EC difference between methods did have a moderate positive correlation with indicators of secondary organic aerosol and sulfate suggesting that oxidized organic aerosol associated with atmospheric processing or other secondary components of ambient aerosol could be associated with the seasonal differences between these EC measurements.

Long-range transport of biomass burning emissions based on organic molecular markers and carbonaceous thermal distribution.

Semi-continuous organic carbon (OC), elemental carbon (EC), and organic molecular markers were analyzed using the thermal optical transmittance method at the Gosan supersite (on Jeju Island, Korea), which has been widely used as a regional background site for East Asia. The Carbonaceous Thermal Distribution (CTD) method, which can provide detailed carbon signature characteristics relative to analytical temperature, was used to improve the carbon fractionation of the analytical method. Ground-based measurements were conducted from October 25 to November 5, 2010. During the sampling period, one high OC concentration event and two characteristic periods were observed. Considering the thermal distribution patterns, the relationship between the EC and black carbon (BC) by optical measurements, the backward trajectories, the aerosol optical thickness, the PM10 concentrations from the 316 PM-network sites that were operated by the Ministry of Environment in Korea, and the organic molecular markers, such as levoglucosan, PAHs, and organic acids, we concluded that the event was influenced by long-range transport from biomass burning emissions. This study discusses the CTD analysis with organic molecular marker concentrations, extracts and interprets additional carbon fractions from a semi-continuous data set, and provides knowledge regarding the origin of carbon sources and their behaviors.

Chemical Characteristics and Formation Pathways of Humic Like Substances (HULIS) in PM 2.5 in an Urban Area

Little information on HUmic-Like Substances (HULIS) in ambient particulate matter has been reported yet in Korea. HULIS makes up a significant fraction of the water-soluble organic mass in the atmospheric aerosols and influence their water uptake properties. In this study 24-hr PM2.5 samples were collected between December 2013 and October 2014 at an urban site in Gwangju and analyzed for organic carbon (OC), elemental carbon (EC), watersoluble OC (WSOC), HULIS, and ionic species, to investigate possible sources and formation processes of HULIS. HULIS was separated using solid phase extraction method and quantified by total organic carbon analyzer. During the study period, HULIS concentration ranged from 0.19 to 5.65 μgC/m with an average of 1.83±1.22 μgC/m, accounting for on average 45% of the WSOC (12~73%), with higher in cold season than in warm season. Strong correlation of WSOC with HULIS (R = 0.91) indicates their similar chemical characteristics. On the basis of the relationships between HULIS and a variety of chemical species (EC, K, NO3-, SO4, and oxalate), it was postulated that HULIS observed during summer and winter were likely attributed to secondary formation and primary emissions from biomass burning (BB) and traffics. Stronger correlation of HULIS with K, which is a BB tracer, in winter (R = 0.81) than in summer (R = 0.66), suggests more significant contribution of BB emissions in winter to the observed HULIS. It is interesting to note that BB emissions may also have an influence on the HULIS in summer, but further study using levoglucosan that is a unique organic marker of BB emissions is required during summer. Higher correlation between HULIS and oxalate, which is mainly formed through cloud processing and/or photochemical oxidation processes, was found in the summer (R = 0.76) than in the winter (R = 0.63), reflecting a high fraction of secondary organic aerosol in the summer.

Characteristics of Carbonaceous Aerosols Measured at Gosan - Based on Analysis of Thermal Distribution by Carbon Analyzer and Organic Compounds by GCMS

Abstract Ground-based measurements were conducted from August 25 to September 8 of 2011 for understandingcharacteristics of carbonaceous aerosols measured at Gosan. Chemical components and their sources werediscussed by analysis of organic compounds with identification of primary and secondary products in particulatematter. Thus, organic carbon (OC) and elemental carbon (EC) based on the carbonaceous thermal distribution(CTD), which provides detailed carbon signature characteristics relative to analytical temperature, was used toimprove the carbon fractionation of the analytical method. In addition, organic compounds by gas chromatographytechnique with the backward trajectories were discussed for characteristics of carbonaceous aerosols. Different air-masses were classified related to the OC thermal signatures and the organic molecular markers such as aromaticacids and PAHs. We concluded that the aging process was influenced by the long-range transport from East Seaarea. Key words : Organic, Organic compounds, OC, EC