OCEC Analyzer Research Articles

A Filter-Based Approach for the Measurement of Mass Absorption Coefficient of OC and EC Components in Soot

ABSTRACT There is a general consensus that soot produced by hydrocarbon combustion consists of two components, elemental carbon associated with the graphitic nanostructure and organic carbon. Despite the relevance of evaluating their radiative properties, particularly for organic carbon, the knowledge of the spectral absorption behavior remains limited. In this work, a dual-beam five wavelengths absorption photometer is used to estimate the optical properties of particulate matter generated by a laminar premixed ethylene-air flame at different residence times along the flame. The wavelength dependence of the light absorption of aerosols collected on filters is analyzed in terms of both the optical band gap and the absorption Ångström exponent, AAE. The aerosols are then analyzed in terms of the organic and elemental carbon content by a thermal-optical OC-EC analyzer. Combining the results of light absorption and OC-EC analysis, the spectral mass absorption coefficient of both the organic carbon and elemental carbon components in soot are obtained.

Secondary sources of PM2.5 based on the vertical distribution of organic carbon, elemental carbon, and water-soluble ions in Bangkok

Ambient PM2.5 pollution can affect human health and the environment in global megacities. Secondary PM2.5 is produced by physical and chemical reactions of primary air pollutants. Sources of secondary PM2.5 in Bangkok have been considered in most on-target investigations for the control and management of air quality. This research aims to identify the vertical distribution of secondary PM2.5 sources in Bangkok, Thailand. Vertical distributions of PM2.5 in haze and non-haze periods were collected at different heights (30, 75, and 110 m above ground level) at the Air Pollutants Monitoring Tower, Kasetsart University (KU tower) between November 2020 and July 2021. The carbon components were analyzed by an OCEC analyzer using the IMPROVE thermal/optical reflectance (TOR) protocol, and the ionic species were determined by ion chromatography. The results showed that the organic carbon (OC) to elemental carbon (EC) ratios of PM2.5 tended to increase with altitude at 30, 75, and 110 m in the range of 2.0 - 7.7, 3.4 - 8.0 and 3.0 - 16.6, respectively. In the haze period (Jan-Feb 2021), the SOC within PM2.5 was the highest at 110 m which was 24.5%. In addition, the key components of SOC, NO3−, NH4+, and SO42− within PM2.5 were found in secondary aerosols in Bangkok. The chemical compositions indicated that secondary PM2.5 is mainly contributed by local vehicle exhaust (30 m) and long-range transported biomass burning (75 and 110 m). This research provides useful information that could be applied for urban secondary PM2.5 control and management.

Implications of Site‐specific Mass Absorption Cross‐section (MAC) to Black Carbon Observations at a High‐altitude Site in the Central Himalaya

Accurate estimation of black carbon (BC) from the widely used optical attenuation technique is important for the reliable assessment of their climatic impact. The optical instruments use Mass Absorption Cross-section (MAC) for converting light attenuation records to BC mass concentrations and Aethalometer is a widely used optical instrument for BC estimation. Several studies have shown large variability in MAC values. It is thus necessary to examine the accuracy and consistency of MAC values obtained using Aethalometer over distinct geographic locations and seasons. In the present study, MAC values are derived using simultaneous observations (2014–2017) from an EC-OC analyzer and an Aethalometer (AE-42) over a high altitude central Himalayan site at Nainital (29.4oN, 79.5oE, 1958 a.m.s.l). The observations reveal that the annual mean value of MAC (5.03 ± 0.03 m2g− 1 at 880nm) is significantly lower than the constant value used by the manufacturer (16.6 m2g− 1 at 880nm). The estimated MAC values also showed significant seasonal variation, spanning over a range from 3.7 to 6.6 m2g− 1. It is found that the seasonal variability of elemental carbon (EC), air mass variation and meteorological parameters play an important role in the changes in MAC values over this region. Multi-wavelength determination of MAC shows the contribution of absorption by species other than EC at shorter wavelengths. MAC does not show a clear diurnal variation, unlike EC and absorption coefficient. The slope of EC vs. corrected equivalent black carbon (eBC) showed a significant improvement during all seasons when compared with uncorrected eBC. This lends credibility to the fact that the use of site-specific MAC leads to more reliable estimates of eBC over the central Himalayan region. It is found that, instead of using the site specific MAC value, had we used the one supplied by the instrument, we would have underestimated the radiative forcing by about 7.8Wm− 2 which amounts to a reduction by 24 %.

Evaluation of the Semi-Continuous OCEC analyzer performance with the EUSAAR2 protocol

This work evaluates the applicability of the reference protocol EUSAAR2 in the Semi-Continuous OCEC analyzer under two environments, an urban background site influenced by traffic emissions and a regional background site. The comparison of the 24-h averaged OC and EC measurements of the Semi-Continuous analyzer with the OC and EC concentrations determined offline in PM2.5 24 h filters yielded very good agreement for both denuded and undenuded samples. In the urban background site, the regression for EC yielded a slope of 0.93 and 1.04 (b = 0.07 and 0.05, R2 = 0.83 and 0.84), for denuded and undenuded samples respectively. The slopes of OC regressions were 0.99 (b = −0.18, R2 = 0.81) for the low volume and 0.93 (b = 0.12, R2 = 0.84) for the high volume samples. In the regional background site, the slopes of the EC regression with the denuded and undenuded samples was 0.91 and 1.02 correspondingly (b = 0 and − 0.03, R2 = 0.77 and 0.89). The regression of OC had slopes close to 1; 1.03 for the high volume and 0.95 for the low volume sampler (b = 0.08 and 0.26, R2 = 0.78 and 0.78). BC measurements obtained by an aethalometer and MAAP were in very good agreement with EC at both sampling sites. BC levels were consistently higher than EC (slope of the regression aethalometer BC vs EC slope a = 1.2, intercept b = 0.19, R2 = 0.79, for the urban background site and a = 1.9, b = −0.04, R2 = 0.94, for the regional site, slope MAAP BC vs EC a = 1.2, b = 0.06, R2 = 0.94, for the urban background site and 1.7, b = −0.03, R2 = 0.96, for the regional site). This confirms the need of using the site-specific mass absorption cross section (MAC) instead of the ones provided by manufacturers for the conversion of absorption units into BC mass concentration. BC data correlated very well with the optical EC obtained from the semi-continuous OCEC analyzer (a = 1.3, b = 0.16, R2 = 0.80 for the urban background site and a = 1.7, b = 0.009, R2 = 0.94 for the regional site, respectively). The comparison of OC concentrations by the Semi-Continuous Sunset analyzer with organic aerosol online measurements by ACSM showed strong correlations. The ratio OA/OC was 1.9 and 2.3 for the urban background and regional sites. The accumulation of refractory material on the filter, because of prolonged periods of sampling, caused a shift of the split point to the inert mode and changes on PC formation and evolution. Extreme dust outbreaks lead to the overestimation of OC due to the evolution of carbonate in the He mode. Generally, the Sunset Semi-Continuous OCEC analyzer with EUSAAR2 provided robust and consistent measurements with offline thermal-optical analysis.

Optical Absorption Properties of Brown Carbon Aerosols in Guangzhou

In this work, we conducted measurements using a seven-wavelength aethalometer, an online OCEC analyzer, and a MARGA to investigate brown carbon (BrC) absorption properties and source origins during the winter of 2014 at Panyu station, Guangzhou. The results showed that the average absorption contributions of BrC decreased with an increase in wavelength, measured as 25.9%, 19.7%, 14.1%, 11.6%, and 7.7% at 370 nm, 470 nm, 520 nm, 590 nm, and 660 nm, respectively. Diurnal variations in BrC absorption and the concentrations of potassium cations (K+) and organic carbon (OC) was high at night and low during the day, which was attributed to biomass burning. This indicated that BrC was emitted from straw burning in rural areas and accumulated in the steady planetary boundary layer at night. Diurnal variations in the ratio of BrC absorption to OC concentrations showed a distinct dip during the afternoon, indicating that aged aerosol and secondary organic aerosol (SOA) had a weaker BrC absorption capacity. There was a good overall correlation between BrC absorption and K+ concentrations. BrC absorption was also moderately related to the concentrations of ammonium cations (NH4+) and nitrate anions (NO3-).

Chemical Characterization of Fine Atmospheric Particles of Water-Soluble Ions and Carbonaceous Species in a Tropical Urban Atmosphere over the Eastern Indo-Gangetic Plain

ABSTRACT Ambient fine aerosols and their sources were evaluated in an eastern Indian megacity, Kolkata (KOL), from September 2010 to August 2011. A submicron aerosol sampler (SAS) with two stage stacked filter units (SFU) was devised for simultaneous but discrete collection of water-soluble inorganic ions (WSII) and carbonaceous aerosols (CA; elemental carbon (EC) and organic carbon (OC)). Characteristics of the WSII and CA were identified using ion chromatography and an OC-EC analyzer, respectively, adopting the Interagency Monitoring of PROtected Visual Environments (IMPROVE-A) protocol. The mean annual concentrations of the WSII showed a predominance of cations (anions), consisting of Ca2+, Mg2+, and Na+ (Cl–, NO3–, and SO42–), with secondary aerosols (NH4+, NO3–, and SO42–) and Ca2+ each constituting 25% and 30%, respectively, of the total WSII (TWSII). The highest mean monthly concentration of SO42– and NO3– was observed during the winter month of February and the summer months of March and May, respectively. A pronounced peak in the monthly mean for the non-sea salt-K+ (nss-K+) concentration was noticed during October and April, implying the strong influence of biomass burning emissions during these months. Among the sea salt (SS), anthropogenic (AN), and dust (DT) sources of the TWSII, a predominant contribution from DT in August and from AN in November, April, and May was inferred. The mean annual concentration of OC was three times higher than that of EC, with 43% of it being secondary OC. Whereas the major sources of OC were inferred to be paved dust, coal combustion, and biomass burning, those of EC were industrial and motor-vehicle non-exhaust emissions, coal combustion, and motor vehicle exhaust.

Comparison of Several DPM Field Monitors for Use in Underground Mining Applications

ABSTRACT To improve worker health protection and support engineering applications in underground mines, such as ventilation-on-demand, capabilities are increasingly sought for continuous monitoring of diesel particulate matter (DPM). For near real-time monitoring over periods up to a full workshift, the FLIR Airtec handheld monitor was developed and calibrated to the NIOSH Standard Method 5040 measure of elemental carbon (EC), which is commonly used as an analytical surrogate for DPM. However, needs still exist for autonomous monitoring over longer periods (e.g., weeks to months). To meet those needs, two commercially available instruments are considered here, the Magee Scientific AE33 Aethalometer and the Sunset Laboratory Semi-continuous OC-EC Field Analyzer. Along with a prototyped monitor called the Airwatch, these were tested head-to-head against the Method 5040 EC and the Airtec in a controlled laboratory setting; and against one another in a field study at an underground mine. Key findings include: the OC-EC field analyzer performed well across a wide range of EC concentrations; the AE33 performed well at relatively low concentrations, but modifications or additional data corrections are likely needed at higher concentrations; and the Airwatch showed good potential, though significant improvements will be required if this instrument is to be further developed, including resolution of several mechanical issues and selection of an appropriate filter material and development of robust data corrections. Moreover, the relative advantages and disadvantages associated with each instrument (e.g., in terms of data quality, complexity and maintenance) must be considered in the context of the intended application and sampling environment.

Carbonaceous aerosol in ambient air: Parallel measurements between water cyclone and carbon analyzer

A water cyclone, developed to collect and preserve biological aerosols in a small liquid flow, was interfaced with a total organic carbon analyzer to measure the aerosol organic and inorganic carbon fractions. The total carbon was compared against parallel measurements of elemental carbon (EC) and organic carbon (OC) using a Sunset Real Time ECOC Analyzer between 12–29 January 2009. A National Institute for Occupational Safety and Health (NIOSH) like protocol for the measurements included four temperature steps ending at 840°C for OC under a helium atmosphere followed by two temperature steps ramped to 850°C for EC in a helium–oxygen atmosphere. Carbon data comparison between the water cyclone-TOC and the TOC measured by the analyzer indicated good agreement (r2=0.82, linear regression slope=0.98, p<0.001). Analyses of the relationship between total water organic carbon and OC, investigated using data sets from case studies spanning two different events, suggested it was possible to distinguish between the primary and secondary sources.

Reduction of particle emissions from gasoline vehicles with direct fuel injection systems using a gasoline particulate filter

To analyze the effect of a gasoline particulate filter (GPF) attachment on the emissions of gasoline direct injection (GDI) vehicles, this study compares the emission results of three types of vehicles: conventional GDI vehicles, vehicles with a GPF at the close-couple catalytic converter (CCC), and vehicles with a GPF at the under-floor catalytic converter (UCC). Regulated particulate matter (PM) and particle number (PN) emitted from test vehicles were measured using gravimetric methods and condensation particle counter (CPC) equipment. In addition, this study analyzed nanoparticle size distribution, organic carbon (OC), elemental carbon (EC), and ammonia (NH3) using EEPS, OC-EC analyzer, and HFIR equipment. In cases of regulated particle emissions, both PM and PN satisfy EURO 6c and are reduced when a GPF is attached. Particulate emissions are especially reduced when the GPF is attached at the UCC position. This is believed to be why a soot layer is formed in stable flow. Emissions of nanoparticles and OC/EC are high in US06 mode at high driving speed. This is considered to be the influence of the regeneration of the GPF as the temperature of the exhaust gas rises. The emission of NH3 is also highest in US06 mode, which is related to catalytic conversion efficiency.

Evaluation and Inter-Comparison of Oxygen-Based OC-EC Separation Methods for Radiocarbon Analysis of Ambient Aerosol Particle Samples

Radiocarbon analysis is a widely-used tool for source apportionment of aerosol particles. One of the big challenges of this method, addressed in this work, is to isolate elemental carbon (EC) for 14C analysis. In the first part of the study, we validate a two-step method (2stepCIO) to separate total carbon (TC) into organic carbon (OC) and EC against the EUSAAR_2 thermal-optical method regarding the recovered carbon concentrations. The 2stepCIO method is based on the combustion of OC in pure oxygen at two different temperature steps to isolate EC. It is normally used with a custom-built aerosol combustion system (ACS), but in this project, it was also implemented as a thermal protocol on a Sunset OC-EC analyzer. Results for the recovered EC mass concentration showed poor agreement between the 2stepCIO method on the ACS system and on the Sunset analyzer. This indicates that the EC recovery is sensitive not only to the temperature steps, but also to instrument-specific parameters, such as heating rates. We also found that the EUSAAR_2 protocol itself can underestimate the EC concentration on untreated samples compared to water-extracted samples. This is especially so for highly loaded filters, which are typical for 14C analysis. For untreated samples, the EC concentration on long-term filter samples (two to five days sampling time) was 20–45% lower than the sum of EC found on the corresponding 24-h filter samples. For water-extracted filter samples, there was no significant difference between long-term and the sum of daily filter samples. In the second part of this study, the 14C was measured on EC isolated by the 2stepCIO method and compared to methods from two other laboratories. The different methods agree well within their uncertainty estimates.

Intercomparison of methods to estimate black carbon emissions from cookstoves

Black carbon is the second largest contributor to climate change and also poses risks to human health. Despite the need for black carbon (BC) emissions estimates from residential biomass burning for cooking, quantitative data are still scarce. This scarcity is mainly due to the scattered location of the stoves, as well as relatively costly and complex analytical methods available. Two low cost and easy-to-use optical methods, a cell-phone based system and smoke stain reflectometry, where compared to elemental carbon (EC) concentrations by the Sunset OCEC Analyzer (TOT). The three techniques were challenged with different aerosol types (urban and biomass cookstoves), and different filter substrates (quartz and glass fibre). A good agreement was observed between the two low cost techniques and the reference system for the aerosol types and concentrations assessed, although the relationship was statistically different for each type of aerosol. The quantification of correction factors with respect to the reference method for the specific conditions under study is essential with either of the low-cost techniques. BC measurements from the cell-phone system and the reflectometer were moderately affected by the filter substrate. The easy use of the cell-phone based system may allow engaging cookstove users in the data collection process, increasing the amount and frequency of data collection which may, otherwise, not be feasible in resourced constrained locations. This would help to raise public awareness about environmental and health issues related to cookstoves.

Role of organic aerosols in CCN activation and closure over a rural background site in Western Ghats, India

The cloud condensation nuclei (CCN) closure study was performed to exemplify the effect of aerosol chemical composition on the CCN activity of aerosols at Mahabaleshwar, a high altitude background site in the Western Ghats, India. For this, collocated aerosol, CCN, Elemental Carbon (EC), Organic Carbon (OC), sub-micron aerosol chemical speciation for the period from 3rd June to 19th June 2015 was used. The chemical composition of non-refractory particulate matter (<1 μm) as measured by Time of Flight – Aerosol Chemical Speciation Monitor (ToF-ACSM) was dominated by organics with average concentration of 3.81 ± 1.6, 0.32 ± 0.06, 0.15 ± 0.02, 0.13 ± 0.03 and 0.95 ± 0.12 μg m−3 for organics, ammonium, chloride, nitrate and sulphate, respectively. The PM1 number concentration as obtained by Wide Range Aerosol Spectrometer (WRAS) varied from 750 to 6480 cm−3. The average mass concentration of elemental carbon (EC) as measured by OC-EC analyzer was 1.16 ± 0.4 μg m−3. The average CCN concentrations obtained from CCN counter (CCNC) at five super-saturations (SS's) was 118 ± 58 cm−3 (0.1% SS), 873 ± 448 cm−3 (0.31% SS), 1308 ± 603 cm−3 (0.52% SS), 1610 ± 838 cm−3 (0.73% SS) and 1826 ± 985 cm−3 (0.94% SS). The CCN concentrations were predicted using Köhler theory on the basis of measured aerosol particle number size distribution, size independent NR-PM1 chemical composition and calculated hygroscopicity. The CCN closure study was evaluated for 3 scenarios, B-I (all soluble inorganics), B-IO (all soluble organics and inorganics) and B-IOOA (all soluble inorganic and soluble oxygenated organic aerosol, OOA). OOA component was derived from the positive matrix factorization (PMF) analysis of organic aerosol mass spectra. Considering the bulk composition as internal mixture, CCN closure study was underestimated by 16–39% for B-I and overestimated by 47–62% for B-IO. The CCN closure result was appreciably improved for B-IOOA where the knowledge of OOA fraction was introduced and uncertainty reduced to within 8–10%.

A field measurement based scaling approach for quantification of major ions, organic carbon, and elemental carbon using a single particle aerosol mass spectrometer

Single Particle Aerosol Mass Spectrometers (SPAMS) have been increasingly deployed for aerosol studies in Asia. To date, SPAMS is most often used to provide unscaled information for both the size and chemical composition of individual particles. The instrument's lack of accuracy is primarily due to only a fraction of particles being detected after collection, and the instrumental sensitivity is un-calibrated for various chemical species in mixed ambient aerosols. During a campaign from January to April 2013 at a coastal site in Hong Kong, the particle number information and ion intensity of major PM2.5 components collected by SPAMS were scaled by comparing with collocated bulk PM2.5 measurements of hourly or higher resolution. The bulk measurements include PM2.5 mass by a SHARP 5030 Monitor, major ions by a Monitor for Aerosols & Gases in ambient Air (MARGA), and organic carbon (OC) and elemental carbon (EC) by a Sunset OCEC analyzer. During the data processing, both transmission efficiency (scaled with the Scanning Mobility Particle Sizer) and hit efficiency conversion were considered, and component ion intensities quantified as peak area (PA) and relative peak area (RPA) were analyzed to track the performance. The comparison between the scaled particle mass assuming a particle density of 1.9 g cm−3 from SPAMS and PM2.5 concentration showed good correlation (R2 = 0.81) with a slope of 0.814 ± 0.004. Regression analysis results suggest an improved scaling performance using RPA compared with PA for most of the major PM2.5 components, including sulfate, nitrate, potassium, ammonium, OC and EC. Thus, we recommend preferentially scaling these species using the RPA. For periods of high K+ concentrations (>1.5 μg m−3), under-estimation of K+ by SPAMS was observed due to exceeding the dynamic range of the acquisition board. When only applying the hit efficiency correction, data for sulfate, nitrate, ammonium, potassium and OC were in reasonably good correlation (R2 = 0.56–0.79) with the bulk measurements, suggesting semi-quantified data by the hit efficiency correction can be utilized when transmission efficiency correction is not available. More inter-comparisons of this type are needed to assess the inter-instrument variability among different SPAMS instruments.

Characterization of carbonaceous aerosols over the urban tropical location and a new approach to evaluate their climatic importance

Increasing emissions from fossil-fuel, biomass burning, land use changes and industrial growth have led to rapid increase in the atmospheric concentrations of carbonaceous species over many cities in India. The present paper deals with the results obtained from year long (2012–13) observations conducted at a tropical urban location, Pune in southwestern India on Organic and Elemental Carbon as well as Black Carbon; using the Sunset OCEC Analyzer and Aethalometer, respectively. The average mass concentrations of OC and EC were in the order of winter > post-monsoon > summer > monsoon. Mean annual OC/EC ratio was found to be 2.4 ± 1.1 during the study period, suggesting the presence of secondary organic carbon (SOC). Estimated SOC was found to form 47% of OC mass concentration. OC and EC were also significantly well correlated (r = 0.95, p < 0.0001) to each other, indicating towards common combustion sources. The primary organic carbon (POC) dominated over SOC and EC in post-monsoon and winter seasons indicating impact of anthropogenic burning activity, enhanced by prevailing meteorological conditions as well as that of long range transport. Mean annual POC + EC/TC ratio was 0.69 indicating that more than 2/3 of TC is formed from combustion sources. Thermally derived EC and optically derived BC correlated very well (r = 0.98, p < 0.0001). A new concept e.g. Effective carbon ratio (ECR) is suggested to better assess the scattering/absorptive nature and probable source identification of carbonaceous aerosols in place of conventional OC/EC ratio.

Characterization of carbonaceous aerosols over Delhi in Ganga basin: seasonal variability and possible sources.

The mass concentration of carbonaceous species, organic carbon (OC), and elemental carbon (EC) using a semicontinuous thermo-optical EC-OC analyzer, and black carbon (BC) using an Aethalometer were measured simultaneously at an urban mega city Delhi in Ganga basin from January 2011 to May 2012. The concentrations of OC, EC, and BC exhibit seasonal variability, and their concentrations were ∼2 times higher during winter (OC 38.1 ± 17.9 μg m(-3), EC 15.8 ± 7.3 μg m(-3), and BC 10.1 ± 5.3 μg m(-3)) compared to those in summer (OC 14.1 ± 4.3 μg m(-3), EC 7.5 ± 1.5 μg m(-3), and BC 4.9 ± 1.5 μg m(-3)). A significant correlation between OC and EC (R = 0.95, n = 232) indicate their common emission sources with relatively lower OC/EC ratio (range 1.0-3.6, mean 2.2 ± 0.5) suggests fossil fuel emission as a major source of carbonaceous aerosols over the station. On average, mass concentration of EC was found to be ∼38 % higher than BC during the study period. The measured absorption coefficient (babs) was significantly correlated with EC, suggesting EC as a major absorbing species in ambient aerosols at Delhi. Furthermore, the estimated mass absorption efficiency (σabs) values are similar during winter (5.0 ± 1.5 m(2) g(-1)) and summer (4.8 ± 2.8 m(2) g(-1)). Significantly high aerosol loading of carbonaceous species emphasize an urgent need to focus on air quality management and proper impact assessment on health perspective in these regions.

Black Carbon and Elemental Carbon from Postharvest Agricultural-Waste Burning Emissions in the Indo-Gangetic Plain

We compare the mass concentrations of black carbon (BC) and elemental carbon (EC) from different emissions in the Indo-Gangetic Plain (IGP), using optical (Aethalometer; 880 nm) and thermooptical technique (EC-OC analyzer; 678 nm), respectively. The fractional contribution of BC mass concentration measured at two different channels (370 and 880 nm), OC/EC ratio, and non-sea-salt K+/EC ratios have been systematically monitored for representing the source characteristics of BC and EC in this study. The mass concentrations of BC varied from 8.5 to 19.6, 2.4 to 18.2, and 2.2 to 9.4 μg m−3during October-November (paddy-residue burning emission), December–March (emission from bio- and fossil-fuel combustion) and April-May (wheat-residue burning emission), respectively. In contrast, the mass concentrations of EC varied from 3.8 to 17.5, 2.3 to 8.9, and 2.0 to 8.8 μg m−3during these emissions, respectively. The BC/EC ratios conspicuously greater than 1.0 have been observed during paddy-residue burning emissions associated with high mass concentrations of EC, OC, and OC/EC ratio. The Ångström exponent (α) derived from Aethalometer data is approximately 1.5 for the postharvest agricultural-waste burning emissions, hitherto unknown for the IGP. The mass absorption efficiency (MAE) of BC and EC centers at ~1–4 m2 g−1and 2-3 m2 g−1during the entire study period in the IGP.

Variations of carbonaceous aerosols from open crop residue burning with transport and its implication to estimate their lifetimes

Studying the correlations of carbonaceous aerosols (element carbon, EC, and organic carbon, OC) from open biomass burning helps to reduce uncertainties in emission inventories and provides necessary constraints for model simulations. In the present study, we measured apparent elemental carbon (ECa) and OC concentrations at the summit of Mount Tai (Mt. Tai) during intensive open crop residue burning (OCRB) episodes using a Sunset OCEC analyzer. In the fine particle mode, OC and ECa showed strong correlations (r > 0.9) with carbon monoxide (CO). Footprint analysis using the FLEXPART_WRF model indicated that OCRB in Central East China had a significant influence on ambient carbonaceous aerosol loadings at the summit of Mt. Tai. During campaign, ΔECa/ΔCO ratios of OCRB plumes were found to be 14.3 ± 1.0 ng m−3 ppbv at Mt. Tai. This ratio was twice larger than those for urban pollution in CEC, demonstrating that significant emissions of soot particles emitted from OCRB. ΔOC/ΔCO ratio of OCRB plumes was found to be 41.9 ± 2.6 ng m−3 ppbv averagely. The transport time of smoke particles was estimated using the FLEXPART_WRF tracer model by releasing particles from the ground layer inside geographical regions where large numbers of hotspots were detected by the MODIS sensor. The relationship between transport time and observed ΔECa/ΔCO and ΔOC/ΔCO ratios was fitted by an e-folding exponential function. Results showed that the loss rate of OC (normalized by CO) with transport was much quicker than that of ECa mass, and the corresponding lifetime of OC mass was estimated to be 28.0–44.2 h (1.2–1.8 days), much shorter than that 98.4–136.9 h (4.1–5.7 days) of ECa. Lifetime of ECa estimated for the OCRB events in CEC in the study was comparably lower than the values normally calculated by the transport models. Short lifetime of OC highlighted its vulnerability to cloud scavenging in the presence of water-soluble organic species from biomass combustion.

Reduction of black carbon aerosols in Tokyo: Comparison of real-time observations with emission estimates

Abstract Black carbon (BC) aerosols alter the radiation budget both directly (by absorbing solar visible radiation) and indirectly (by acting as cloud condensation nuclei) and cause adverse health effects. The absorbing efficiency and direct radiative effect of BC strongly depend on its mass concentration (MBC) and type of emission source. In the present study, we report measurements of MBC at the Research Center for Advanced Science and Technology (RCAST), located at the center of the urban boundary of Tokyo, using an EC-OC analyzer from 2003 to 2005 and a filter-based Continuous Soot Monitoring System (COSMOS) during 2007–2010. The results indicate that MBC have decreased significantly from 2.6 μg m−3 to 0.5 μg m−3 (∼80% reduction) between 2003 and 2010. Vehicular emissions are the dominant source of BC in Tokyo, and the observed reduction in MBC is mainly attributed to the stringent regulations of particulate matter exhaust from vehicles imposed by the Japanese government. In addition, this observation is also supported from emission estimates using diurnal-weekly variations of MBC in Tokyo and explains the observed reduction to within about 20%. This is the first clear evidence of a significant reduction in BC emissions in Tokyo and shows that measures taken to reduce BC emissions from traffic sources have a strong effect on air quality in a mega-city and also reduce the climate impact of traffic emissions. We highlight the importance of long-term and reliable measurements in detecting BC trends and for the validation and regulation of emission control measures in mega-cities.

Quantification of aerosol chemical composition using continuous single particle measurements

Abstract. Mass concentrations of sulphate, nitrate, ammonium, organic carbon (OC), elemental carbon (EC) were determined from real time single particle data in the size range 0.1–3.0 μm measured by an Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) at urban and rural sites in Canada. To quantify chemical species within individual particles measured by an ATOFMS, ion peak intensity of m/z −97 for sulphate, −62 for nitrate, +18 for ammonium, +43 for OC, and +36 for EC were scaled using the number and size distribution data by an Aerodynamic Particle Sizer (APS) and a Fast Mobility Particle Sizer (FMPS). Hourly quantified chemical species from ATOFMS single-particle analysis were compared with collocated fine particulate matter (aerodynamic diameter &lt; 2.5 μm, PM2.5) chemical composition measurements by an Aerosol Mass Spectrometer (AMS) at a rural site, a Gas-Particle Ion Chromatograph (GPIC) at an urban site, and a Sunset Lab field OCEC analyzer at both sites. The highest correlation was found for nitrate, with correlation coefficients (Pearson r) of 0.89 (ATOFMS vs. GPIC) and 0.85 (ATOFMS vs. AMS). ATOFMS mass calibration factors, determined for the urban site, were used to calculate mass concentrations of the major PM2.5 chemical components at the rural site near the US border in southern Ontario. Mass reconstruction using the ATOFMS mass calibration factors agreed very well with the PM2.5 mass concentrations measured by a Tapered Element Oscillating Microbalance (TEOM, r = 0.86) at the urban site and a light scattering monitor (DustTrak, r = 0.87) at the rural site. In the urban area nitrate was the largest contributor to PM2.5 mass in the winter, while organics and sulphate contributed ~64 % of the summer PM2.5 in the rural area, suggesting a strong influence of regional/trans-boundary pollution. The mass concentrations of five major species in ten size-resolved particle-types and aerosol acidity of each particle-type were determined for the rural site. On a mass basis sulphate and OC rich particle-types (OC-S and OC-S-N) accounted for up to 59 % of the particles characterized and aerosols were weakly acidic in the rural area. This is the first study to estimate hourly quantitative data of sulphate, nitrate, ammonium, OC and EC in ambient particles from scaled ATOFMS single particle analysis; these were closely comparable with collocated high time resolution data of sulphate, nitrate and ammonium detected by AMS and GPIC.

Inter-comparison of thermal and optical methods for determination of atmospheric black carbon and attenuation coefficient from an urban location in northern India

The simultaneous measurements of black carbon (BC, based on Aethalometer) and elemental carbon (EC, using thermo-optical EC–OC analyzer) in airborne particles collected from an urban location (Kanpur) in northern India are reported here. The strategy for site-selection is most relevant in order to assess the relative dominance of emissions from coal-fired industries, fossil–fuel combustion and biomass burning on the seasonal variability of EC (BC) concentrations. An inter-comparison of the analytical data ( n = 32) suggests that BC mass concentration is ∼ 20% higher than that of EC. However, attenuation coefficient ( b ATN) measured by the two analytical instruments shows good agreement (slope = 0.97, n = 27), establishing the validity of b ATN derived from thermo-optical EC–OC analyzer. Furthermore, slope (20.7 m 2 g − 1 ) of a linear-fit to the data ( n = 48, R 2 = 0.86) for surface EC concentration (EC s ≤ 8 μg C cm − 2 ) and optical-attenuation (ATN ≤ 180) measured at 678 nm on thermo-optical analyzer provides an independent and novel way of determining the “site-specific” attenuation cross-section ( σ ATN).