Oliver V. Rattigan

Characterization of Residential Wood Combustion Particles Using the Two-Wavelength Aethalometer

In the United States, residential wood combustion (RWC) is responsible for 7.0% of the national primary PM(2.5) emissions. Exposure to RWC smoke represents a potential human health hazard. Organic components of wood smoke particles absorb light at 370 nm more effectively than 880 nm in two-wavelength aethalometer measurements. This enhanced absorption (Delta-C = BC(370 nm) - BC(880 nm)) can serve as an indicator of RWC particles. In this study, aethalometer Delta-C data along with measurements of molecular markers and potassium in PM(2.5) were used to identify the presence of airborne RWC particles in Rochester, NY. The aethalometer data were corrected for the loading effect. Delta-C was found to strongly correlate with wood smoke markers (levoglucosan and potassium) during the heating season. No statistically significant correlation was found between Delta-C and vehicle exhaust markers. The Delta-C values were substantially higher during winter compared to summer. The winter diurnal pattern showed an evening peak around 21:00 that was particularly enhanced on weekends. A relationship between Delta-C and PM(2.5) was found that permits the estimation of the contribution of RWC particles to the PM mass. RWC contributed 17.3% to the PM(2.5) concentration during the winter. Exponential decay was a good estimator for predicting Delta-C concentrations at different winter precipitation rates and different wind speeds. Delta-C was also sensitive to remote forest fire smoke.

New York State urban and rural measurements of continuous PM2.5 mass by FDMS, TEOM, and BAM.

Abstract Field evaluations and comparisons of continuous fine particulate matter (PM2.5) mass measurement technologies at an urban and a rural site in New York state are performed. The continuous measurement technologies include the filter dynamics measurement system (FDMS) tapered element oscillating microbalance (TEOM) monitor, the stand-alone TEOM monitor (without the FDMS), and the beta attenuation monitor (BAM). These continuous measurement methods are also compared with 24-hr integrated filters collected and analyzed under the Federal Reference Method (FRM) protocol. The measurement sites are New York City (the borough of Queens) and Addison, a rural area of southwestern New York state. New York City data comparisons between the FDMS TEOM, BAM, and FRM are examined for bias and seasonality during a 2-yr period. Data comparisons for the FDMS TEOM and FRM from the Addison location are examined for the same 2-yr period. The BAM and FDMS measurements at Queens are highly correlated with each other and the FRM. The BAM and FDMS are very similar to each other in magnitude, and both are ∼25% higher than the FRM filter measurements at this site. The FDMS at Addison measures ∼9% more mass than the FRM. Mass reconstructions using the speciation trends network filter data are examined to provide insight as to the contribution of volatile species of PM2.5 in the FDMS mass measurement and the fraction that is likely lost in the FRM mass measurement. The reconstructed mass at Queens is systematically lower than the FDMS by ∼10%.

Semicontinuous PM2.5 sulfate and nitrate measurements at an urban and a rural location in New York: PMTACS-NY summer 2001 and 2002 campaigns.

Abstract Several collocated semicontinuous instruments measuring particulate matter with particle sizes ≤2.5 μm (PM2.5) sulfate (SO4 22−) and nitrate (NO3 −) were intercompared during two intensive field campaigns as part of the PM2.5 Technology Assessment and Characterization Study. The summer 2001 urban campaign in Queens, NY, and the summer 2002 rural campaign in upstate New York (Whiteface Mountain) hosted an operation of an Aerosol Mass Spectrometer, Ambient Particulate Sulfate and Nitrate Monitors, a Continuous Ambient Sulfate Monitor, and a Particle-Into-Liquid Sampler with Ion Chromato-graphs (PILS-IC). These instruments provided near realtime particulate SO4 2− and NO3 − mass concentration data, allowing the study of particulate SO4 2−/NO3 − diurnal patterns and detection of short-term events. Typical particulate SO4 2− concentrations were comparable at both sites (ranging from 0 to 20 μg/m3), while ambient urban particulate NO3 − concentrations ranged from 0 to 11 μg/m3 and rural NO3 − concentration was typically less than 1 μg/m3. Results of the intercomparisons of the semicontinu-ous measurements are presented, as are results of the comparisons between the semicontinuous and time-integrated filter-based measurements. The comparisons at both sites, in most cases, indicated similar performance characteristics. In addition, charge balance calculations, based on major soluble ionic components of atmospheric aerosol from the PILS-IC and the filter measurements, indicated slightly acidic aerosol at both locations.

An Intercomparison of Measurement Methods for Carbonaceous Aerosol in the Ambient Air in New York City

Measurement methods for fine carbonaceous aerosol were compared under field sampling conditions in Flushing, New York during the period of January and early February 2004. In-situ 5- to 60-minute average PM 2.5 organic carbon (OC), elemental carbon (EC), and black carbon (BC) concentrations were obtained by the following methods: Sunset Laboratory field OC/EC analyzer, Rupprecht and Patashnick (R&P) series 5400 ambient carbon particulate monitor, Aerodyne aerosol mass spectrometer (AMS) for total organic matter (OM), and a two-wavelength AE-20 Aethalometer. Twenty-four hour averaged PM 2.5 filter measurements for OC and EC were also made with a Speciation Trends Network (STN) sampler. The diurnal variations in OC/EC/BC concentrations peaked during the morning and afternoon rush hours indicating the dominant influence of vehicle emissions. BC/EC slopes are found to range between 0.86 and 1.23 with reasonably high correlations (r > 0.75). Low mixing heights and absence of significant transported carbonaceous aerosol are indicated by the measurements. Strong correlations are observed between BC and thermal EC as measured by the Sunset instrument and between Sunset BC and Aethalometer BC. Reasonable correlations are observed among collocated OC/EC measurements by the various instruments.

Multiple-year black carbon measurements and source apportionment using Delta-C in Rochester, New York

Black carbon (BC), an important component of the atmospheric aerosol, has climatic, environmental, and human health significance. In this study, BC was continuously measured using a two-wavelength aethalometer (370 nm and 880 nm) in Rochester, New York, from January 2007 to December 2010. The monitoring site is adjacent to two major urban highways (I-490 and I-590), where 14% to 21% of the total traffic was heavy-duty diesel vehicles. The annual average BC concentrations were 0.76 μg/m3, 0.67 μg/m3, 0.60 μg/m3, and 0.52 μg/m3 in 2007, 2008, 2009, and 2010, respectively. Positive matrix factorization (PMF) modeling was performed using PM2.5 elements, sulfate, nitrate, ammonia, elemental carbon (EC), and organic carbon (OC) data from the U.S. Environmental Protection Agency (EPA) speciation network and Delta-C (UVBC370nm – BC880nm) data. Delta-C has been previously shown to be a tracer of wood combustion factor. It was used as an input variable in source apportionment models for the first time in this study and was found to play an important role in separating traffic (especially diesel) emissions from wood combustion emissions. The result showed the annual average PM2.5 concentrations apportioned to diesel emissions in 2007, 2008, 2009, and 2010 were 1.34 μg/m3, 1.25 μg/m3, 1.13 μg/m3, and 0.97 μg/m3, respectively. The BC conditional probability function (CPF) plots show a large contribution from the highway diesel traffic to elevated BC concentrations. The measurements and modeling results suggest an impact of the U.S Environmental Protection Agency (EPA) 2007 Heavy-Duty Highway Rule on the decrease of BC and PM2.5 concentrations during the study period. Implications: This study suggests that there was an observable impact of the U.S EPA 2007 Heavy-Duty Highway Rule on the ambient black carbon concentrations in Rochester, New York. Aethalometer Delta-C was used as an input variable in source apportionment models and it allowed the separation of traffic (especially diesel) emissions from wood combustion emissions. Supplemental Materials: Supplemental materials are available for this article. Go to the publishers online edition of the Journal of the Air & Waste Management Association for additional details on the sampling location, the analyses of the aerosol data, and the alternative PMF analysis omitting Delta-C.

Mercury (Hg) emissions from domestic biomass combustion for space heating

Three mercury (Hg) species (gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and fine particulate-bound mercury (PBM(2.5))) were measured in the stack of a small scale wood combustion chamber at 400°C, in the stack of an advanced wood boiler, and in two areas influenced by wood combustion. The low temperature process (lab-scale) emitted mostly GEM (∼99% when burning wood pellets and ∼95% when burning unprocessed wood). The high temperature wood boiler emitted a greater proportion of oxidized Hg (approximately 65%) than the low temperature system. In field measurements, mean PBM(2.5) concentrations at the rural and urban sites in winter were statistically significantly higher than in warmer seasons and were well correlated with Delta-C concentrations, a wood combustion indictor measured by an aethalometer (UV-absorbable carbon minus black carbon). Overall the results suggest that wood combustion may be an important source of oxidized mercury (mostly in the particulate phase) in northern climates in winter.

Case studies of the SO2 + H2O2 reaction in clouds

The in-cloud reaction between SO2 and H2O2has been investigated using data from field campaigns of July 1995 and July–August 1997 at Whiteface Mountain, New York. Cloud water samples were collected at the mountains summit (1.5 km, above mean sea level (amsl)), and aerosols in clear air at a site (Lodge) located at 0.6 km amsl and in cloud interstitial air at the summit. Cloud water and aerosol samples were analyzed for SO42− and selected trace elements. Gaseous SO2 and H2O2 were measured at both sampling sites. Criteria based on total sulfur and O3 concentrations were developed to decide when the two sites were coupled (i.e., air masses at the two sites had the same composition for the chemical species studied). Four case studies are presented that exhibit varying concentration levels and different meteorological conditions. In two cases the sites were coupled, and in two others they were decoupled. The clouds showed high pollutant concentrations with a mean pH of 3.5. A tracer technique was used to quantitatively determine the SO42− produced from in situ SO2 oxidation. In general, good agreement between the SO2 consumed and SO42− produced was observed. Similarly, H2O2 concentrations in precloud air showed stoichiometric mass balance with the sum of H2O2 observed in cloud interstitial air, in cloud water, and equimolar amounts needed to produce SO4in2− as determined by the tracer technique. Data from all 24 clouds showed that (1) ∼28% of the cloud water SO42− was due to in situ oxidation; (2) ∼75% of the SO2 in the precloud air was oxidized in situ at Whiteface Mountain; (3) the mean SO2 concentration in air masses associated with cloudy periods is approximately 1.4 ppb, significantly higher than the summer average of 0.5 ppb; (4) the mean H2O2 concentration in cloud-free periods during summer is 1.1 ppb sufficient to oxidize SO2 present; (5) the frequent presence of H2O2 in cloud water indicated that the reaction had not often reached completion.

Effect of the shutdown of a large coal-fired power plant on ambient mercury species

In the spring of 2008, a 260MWe coal-fired power plant (CFPP) located in Rochester, New York was closed over a 4month period. Using a 2-years data record, the impacts of the shutdown of the CFPP on nearby ambient concentrations of three Hg species were quantified. The arithmetic average ambient concentrations of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate mercury (PBM) during December 2007-November 2009 were 1.6ngm(-3), 5.1pgm(-3), and 8.9pgm(-3), respectively. The median concentrations of GEM, GOM, and PBM significantly decreased by 12%, 73%, and 50% after the CFPP closed (Mann-Whitney test, p<0.001). Positive Matrix Factorization (EPA PMF v4.1) identified six factors including O3-rich, traffic, gas phase oxidation, wood combustion, nucleation, and CFPP. When the CFPP was closed, median concentrations of GEM, GOM, and PBM apportioned to the CFPP factor significantly decreased by 25%, 74%, and 67%, respectively, compared to those measured when the CFPP was still in operation (Mann-Whitney test, p<0.001). Conditional probability function (CPF) analysis showed the greatest reduction in all three Hg species was associated with northwesterly winds pointing toward the CFPP. These changes were clearly attributable to the closure of the CFPP.

Field and Laboratory Evaluation of the Thermo Electron 5020 Sulfate Particulate Analyzer

The Thermo Electron Model 5020 Sulfate Particulate Analyzer is a recently commercialized instrument that provides continuous measurements of the sulfate component of ambient particulate matter. The technique uses a stainless steel rod placed inside a quartz oven to reduce the particle sulfate to sulfur dioxide; followed by pulsed fluorescence detection of the sulfur dioxide. Field and laboratory evaluations of a pre-production version of the analyzer are described as well as laboratory evaluations of the pre-production version and two production units. Laboratory tests concentrated on challenging the instruments with ammonium sulfate aerosol, but tests with sodium, potassium, and calcium sulfate are reported as well. The instrument performed very well in field and laboratory settings, reporting values that were highly correlated with continuous mass measurements in the lab, and 24-hour filters in the field. Conversion/detection efficiencies for ammonium sulfate in the laboratory, and for ambient sulfate aerosol at our rural site in Addison, New York, were both very close to 80%. Laboratory conversion efficiencies for calcium, sodium, and potassium sulfate salts ranged from 4% to 63%. These lower efficiencies for mineral-type sulfates will be an important consideration in areas with significant concentrations of sea salt or mineral dust sulfate, and less important for the high sulfate Eastern US which is dominated by ammonium sulfate.

Sulfur dioxide oxidation in clouds at Whiteface Mountain as a function of drop size

In situ oxidation of SO2 has been determined in clouds as a function of droplet size using a trace element technique during July 1998 at Whiteface Mountain, New York. The pH of the cloud water ranged from 2.8 to 4.7 with a mean of 3.4, and therefore SO2 oxidation was dominated by hydrogen peroxide. Size-fractioned cloud samples were collected from six different events at the mountains summit (1.5 km above mean sea level) using a size-fractionating California Institute of Technology Active Strand Cloudwater Collector. Bulk samples were collected using both passive and active collectors. During each event, below-cloud and interstitial aerosols were collected every 2 hours. Cloud water and aerosol samples were analyzed for major ions and selected trace elements. Continuous measurements of gas phase species SO2, H2O2, and O3 were carried out at the summit and below-cloud sites. Concentrations of cloud water SO42−, NO3−, H2O2, and trace elements, as well as pH, were largely independent of droplet size. The component of cloud water SO42− produced from in situ oxidation (SO2−4in) was also largely independent of droplet size. The results are in agreement with calculated relative production rates in the small and large drop sizes based on known laboratory reaction rates.