Atmospheric Environment (v.40, #S2)

Field test data for 42 liter per minute PM2.5 aerosol sampler used during the PMTACS-NY intensives held at Queens College, Queens, NY by Vincent A. Dutkiewicz; Sumizah Qureshi; Adil R. Khan; Liaquat Husain; James J. Schwab; Kenneth L. Demerjian (182-191).
A 42 l min−1 (lpm) sampler (Hi-flo) was used to collect 6-h samples during the 2001 summer and the 2004 winter PM2.5 Technology Assessment and Characterization Study-New York (PMTACS-NY) intensives held at Queens College in urban Queens, NY. A sum total of 146 samples collected in 2001 and 113 samples collected in 2004. The samples were water-extracted and analyzed for sulfate by ion chromatography. In addition the 2001 samples had 15 metals determined by inductively coupled plasma mass spectroscopy after water extraction (a soluble fraction) and also after a rigorous microwave digestion (total). The Hi-flo sampler allowed trace metal concentrations to be determined on 6-h samples with nearly the same minimum reporting level (mass loading) as 24-h samplers collected with commercial samplers that operate at 16.7 lpm. We present a comparison of the concentrations of SO4 and 15 selected trace metals measured on the filters collected with Hi-flo and co-located commercial PM2.5 samplers. The Hi-flo sampler is demonstrated to accurately reproduce SO4 and certain elements during the urban intensive. The average slopes of the regressions with a co-located commercial sampler differed from 1 by ±3%. Most aerosol species measured in the 6-h samples collected at Queens College during the 2001 intensive had maximum daily concentrations for the 0600–1200 h sample except sulfate which was maximum for the 1200–1800 h sample and Sb which was uniquely maximum between 0000 and 0600 h. Supporting data suggest afternoon maximum for sulfate is due to more efficient mixing down from aloft the air that was transported from distant sources rather than local photochemistry.
Keywords: Supersites; Particulate matter; Sulfate; Trace elements; PM2.5; Urban aerosols; Aerosol sampling;

Multi-year urban and rural semi-continuous PM2.5 sulfate and nitrate measurements in New York state: Evaluation and comparison with filter based measurements by Oliver V. Rattigan; Olga Hogrefe; H.D. Felton; James J. Schwab; Utpal K. Roychowdhury; Liaquat Husain; Vincent A. Dutkiewicz; Kenneth L. Demerjian (192-205).
Measurements of PM2.5 sulfate and nitrate were carried out over a period of 3 years with a 10-min time resolution, using Rupprecht and Patashnick Co., Inc., (R&P) Ambient Particulate Sulfate and Nitrate Monitors, models 8400S and 8400N, respectively. The instruments were deployed at an urban site in the South Bronx, NY, and at Whiteface Mountain, a rural field monitoring location in upstate New York. At both sites collocated 24-h integrated filter measurements are compared to the semi-continuous sulfate and nitrate data. The sites are also equipped with a suite of gas phase (NO x , SO2, and O3) and other particulate-based instrumentation. The semi-continuous data is used to examine the diurnal, seasonal and yearly variability of PM2.5 sulfate and nitrate at both locations.Clear seasonal trends were observed for both sulfate and nitrate with maximum sulfate concentrations in the warmer months and highest nitrate in the winter–spring periods at both locations. PM2.5 nitrate showed a clear diurnal pattern with peak concentrations in the early morning hours at the South Bronx site. Results of the comparisons between the semi-continuous measurements and 24-h filter data are presented. The potential use of the R&P sulfate and nitrate instruments for routine monitoring is evaluated based on these results, and our operational experiences with the instruments.
Keywords: PM2.5 sulfate; PM2.5 nitrate; Semi-continuous data; Diurnal trends; Ambient aerosols;

An evaluation of current PM2.5 conditions in the US by Shao-Hang Chu; Joseph W. Paisie (206-211).
In this study, all available PM2.5 sites in the United States with more than 5 years of Federal Reference Method data are studied. The critical design values (CDV) for each site are calculated. The CDV concept developed by Chu (Chu, S.-H., 2000. CDV estimation and its applications. Presented at the 93rd AWMA Annual Meeting, San Diego, CA) has proven to be useful in PM10 Limited Maintenance Plan applications (US EPA, 2001. PM10-NAAQS Implementation-Guidance Document—Limit Maintenance Plan Option for Moderate PM10 Nonattainment Areas. US EPA, Research Triangle Park.) because of its ability in predicting the likelihood of future violations of the National Ambient Air Quality Standards (NAAQS) based on the existing design values (DV) and their inter-annual variability. Thus, the potential for future violations of PM2.5 standards among these sites can be estimated and compared. The results suggest that given the current PM2.5 NAAQS, most of the high-risk areas of potential future violation of the annual standard are in the East and California. However, only California and a few isolated areas in the West are at risk of violation of the 24-h standard in the near future. The higher risk of violating the PM2.5 annual NAAQS in the East and California is largely due to the existing high level of average design value (ADV) concentrations. On the other hand, the higher risk of violation of the 24-h NAAQS in the West (essentially California) is largely attributable to inter-annual variability, particularly in natural emissions such as wildfires, since these events play a significant role in the quick rise of short-term PM2.5 levels in the West. The more frequent occurrence of wildfires in the West is known to be associated with its much drier climate and frequent droughts. On the other hand, higher SO2 emissions in a more humid East, particularly in the summer, lead to much higher sulfate concentrations and enhanced secondary organic aerosol production (Chu, S.-H., 2004. PM2.5 episodes as observed in the speciation trends network. Atmospheric Environment 38, 5237–5246). Thus, the much higher annual PM2.5 DVs in the East are largely due to the high level of sulfate and organic aerosol concentrations. These results may be used by the regulators to identify seriously polluted areas and prioritize their regional control strategies.
Keywords: Critical design value; Design value; Inter-annual variability; PM2.5; Ambient air quality standards; Probability;

Chemical composition and mass closure of particulate matter at six urban sites in Europe by Markus Sillanpää; Risto Hillamo; Sanna Saarikoski; Anna Frey; Arto Pennanen; Ulla Makkonen; Zoya Spolnik; René Van Grieken; Martin Braniš; Bert Brunekreef; Marie-Cecile Chalbot; Thomas Kuhlbusch; Jordi Sunyer; Veli-Matti Kerminen; Markku Kulmala; Raimo O. Salonen (212-223).
The chemical composition of fine (PM2.5) and coarse (PM2.5−10) particulate matter was investigated in 7-week field campaigns of contrasting air pollution at six urban background sites in Europe. The campaigns were scheduled to include seasons of local public health concern due to high particulate concentrations or findings in previously conducted epidemiological studies. The sampling campaigns were carried out as follows: Duisburg/Germany October–November 2002 (autumn), Prague/Czech Republic November 2002–January 2003 (winter), Amsterdam/Netherlands January–March 2003 (winter), Helsinki/Finland March–May 2003 (spring), Barcelona/Spain March–May 2003 (spring) and Athens/Greece June–July 2003 (summer). Aerosol samples were collected in 3+4-day periods per week (N=14) using two identical virtual impactors (VI). All the filter samples were analysed with the same instruments to obtain particulate mass, inorganic ions, total and watersoluble elements, and elemental and organic carbon content. The campaign means of PM2.5 and PM2.5−10 ranged from 8.3 to 30 and 5.4 to 29 μg m−3, respectively. The “wet and cool” seasons favoured a low coarse-to-fine particulate mass ratio (<1), whereas the ratio was high (>1) during the warmer and drier spring and summer campaigns. According to chemical mass closure, the major components in PM2.5 were carbonaceous compounds (organic matter+elemental carbon), secondary inorganic ions and sea salt, whereas those in PM2.5−10 were soil-derived compounds, carbonaceous compounds, sea salt and nitrate. The major and minor components together accounted for 79–106% and 77–96% of the gravimetrically measured PM2.5 and PM2.5−10 mass, respectively. In conclusion, the measured PM2.5 and PM2.5−10 in the campaigns could be reconstructed to a large extent with the help of harmonized particulate sampling and analysis of the selected chemical constituents. The health significance of the observed differences in chemical composition and emission sources between the size-segregated particulate samples will be investigated in toxicological cell and animal studies.
Keywords: Chemical mass closure; Chemical components; Fine particles; Coarse particles; Urban aerosol;

Baltimore Supersite: Highly time- and size-resolved concentrations of urban PM2.5 and its constituents for resolution of sources and immune responses by J.M. Ondov; T.J. Buckley; P.K. Hopke; D. Ogulei; M.B. Parlange; W.F. Rogge; K.S. Squibb; M.V. Johnston; A.S. Wexler (224-237).
Protection of public health from the effects of air particulate matter (PM) requires measurements and methods that assess the PM chemical constituents, physical properties, and their sources. Sampling was conducted at three sites in the Baltimore area: a source-oriented (industrial) area in south Baltimore (FMC site), and two receptor area sites (Clifton Park and Ponca Street). FMC measurements were made for the initial 1-month of the project; Clifton measurements lasted for about 2 months, while measurements at Ponca Street lasted for about 9.5 months. Pollutant samples were collected at intervals ranging from 5 min to 1 h using semi-continuous monitors for PM2.5 mass, sulfate, nitrate, elemental and organic carbon, particle number size distributions (10–20,000 nm), CO, NO x , O3, 11 metals, and mass spectra of individual particles, throughout the project. In addition to standard meteorological measurements, a 3D-sonic anemometer and a LIDAR system were operated during selected periods as were a rotating drum impactor with 3- to 6-h resolution and a filter/PUF sampler for 3-h measurements of organic compounds. Standard speciation and FRM mass measurements were also made. This report describes the types of measurements that were made at the various sites of the Baltimore Supersite program as well as presents the summary statistics for some of the PM measurements that have been made. The measurements of aerosol mass, major components, and size distribution data for the three sites are compared. Results show comparable PM concentrations at Ponca Street and Clifton Park. Increased variability was observed at Ponca Street.
Keywords: Baltimore supersite; Particulate matter; Urban PM2.5;

Elemental composition of PM2.5 aerosols in Queens, New York: Solubility and temporal trends by Sumizah Qureshi; Vincent A. Dutkiewicz; Adil R. Khan; Kamal Swami; Karl X. Yang; Liaquat Husain; James J. Schwab; Kenneth L. Demerjian (238-251).
As a part of the PM2.5 Technology Assessment and Characterization Study-New York (PMTACS-NY), concentrations of sulfate and 15 trace elements were determined in daily PM2.5 samples collected from July 2001 to September 2002 at a site in urban Queens, NY. The elements were Mg, Al, Ca, V, Cr, Mn, Fe, Co, Ni, Zn, As, Se, Cd, Sb, and Pb. Over the first 12 months these elemental concentrations were measured in both a water extract and in a total acid digestate so that the solubility of the aerosols bearing the above trace elements could be evaluated. This is important as elements with high solubility can be more readily bio-activated in the lungs and thus may be potentially more harmful to humans. An overview of the elemental composition of PM2.5 aerosols at the Queens, NY site over the 15-month period is presented. This includes a comparison of seasonal changes in aerosol composition and solubility at the sites along with an evaluation of the impacts on aerosol composition of the collapse of the World Trade Center Towers in Manhattan on 9/11/2001 and the smoke from Quebec wildfires in early July 2002.
Keywords: Particulate matter; Sulfate; Trace elements; PM2.5; Urban aerosols; Solubility; World Trade Center collapse; Wildfire smoke;

Behavior of OH and HO2 in the winter atmosphere in New York City by Xinrong Ren; William H. Brune; Jingqiu Mao; Michael J. Mitchell; Robert L. Lesher; James B. Simpas; Andrew R. Metcalf; James J. Schwab; Chenxia Cai; Yongquan Li; Kenneth L. Demerjian; Henry D. Felton; Garry Boynton; Allen Adams; Jacqueline Perry; Yi He; Xianliang Zhou; Jian Hou (252-263).
Hydroxyl (OH) and hydroperxy (HO2) radicals, collectively known as HO x , were measured during an intensive field study in January and February 2004 in New York City. Much less OH and HO2 levels were observed than in the summer of 2001 at the same site. On average, the maximum daytime mixing ratios were 0.05 pptv (1.4×106  cm−3) for OH and 0.7 pptv for HO2, which were about one fifth of the levels in the summer of 2001. A zero-dimensional chemical model, based on the regional atmospheric chemical mechanism (RACM) and constrained by the measured concentrations of O3, NO, NO2, CO, SO2, speciated volatile organic compounds (VOCs) and meteorological parameters, was used to study the HO x chemistry in this environment. The model generally reproduced the daytime OH well, with a median measured-to-model ratio of 0.98. However, HO2 was significantly under-predicted both at day and at night, with a median measured-to-model ratio of 6.0 during daytime. The discrepancy is pronounced when NO concentrations were high, a result that is consistent with some previous studies in urban environments. Photolysis of HONO was the dominant calculated HO x source during daytime; O3 reactions with alkenes became the main calculated HO x source at night. The main calculated HO x sink was the OH reaction with NO2. The discrepancy between measured and modeled HO2 may be caused by significant HO x production that is missing in the model. An additional HO2 production of up to 3×107  cm−3  s−1 (1.1 pptv s−1), which is three times the calculated HO x production, is needed. This HO2 production can come either from unknown new HO x production or from unknown HO2 recycling that does not go through OH.
Keywords: Hydroxyl radical; Hydroperoxy radical; Observation; Winter; Laser-induced fluorescence; Urban atmosphere;

Atmospheric particulate matter (PM) presence at four urban sites in the city of Milan (Italy) is characterised in terms of particle size distribution (number, surface, volume) for the cold and warm season. Simultaneous monitoring of particle number concentration (from 300 nm up to 20 μm of diameter) has been performed between August 2002 and December 2004 by means of a low-volume particle size laser analyser. The monitoring sites are characterised by a different exposure to traffic emissions, enabling for the assessment of the role of this source on both PM concentration levels and on particle size distributions. Data from an urban background site, not directly exposed to traffic emission, a site in a residential area of the city, and two kerbside sites (one at open air, one in a road tunnel) directly exposed to the traffic emissions are compared. Weekdays’ and weekends’ data from the urban background site are analysed for assessing the effect of the reduced traffic circulation on Sundays.Particle concentration is higher at the traffic exposed sites, (where a large increase in particles concentration is observed), especially in the size range between 0.5 and 5 μm, as a consequence of the primary particulate traffic emissions and of the resuspension of soil dust, whereas below 0.5 μm the particle concentrations are similar to those measured in the ambient air.The comparison of seasonal data points out that in the cold season the total number of particles is about two times greater than in the warm season, both on weekdays and on Sundays. In both seasons, particle size distributions present similar patterns, with 99.5% of the total number of particles characterised by a diameter smaller than 1 μm and with Sundays’ distributions shifted towards lower values compared to weekdays’, especially in the coarse size range. According to all these findings, the traffic emissions of the area mainly affect the presence of supermicron particles, while they play only a limited influence on the finest size fractions, characterised by a large background presence, deriving from secondary formation processes in the atmosphere.
Keywords: Particulate matter; Size distribution; Traffic emissions; Weekend effect;

Ammonia has recently gained importance for its increasing atmospheric concentrations and its role in the formation of aerosols. The anaerobic lagoon and spray method, commonly used for waste storage and disposal in confined animal feeding operations (CAFO), is a significant source of ammonia emissions. An accurate emission model for ammonia from aqueous surfaces can help in the development of emission factors. Data collected from field measurements made at hog waste lagoons in south eastern North Carolina, using the flow through dynamic chamber technique, were used to evaluate the Coupled mass transfer and Chemical reactions model and Equilibrium model developed by Aneja et al. [2001a. Measurement and modeling of ammonia emissions at waste treatment lagoon-Atmospheric Interface. Water, Air and Soil pollution: Focus 1, 177–188]. Sensitivity analysis shows that ammonia flux increases exponentially with lagoon temperature and pH, but a linear increase was observed with an increase in total ammoniacal nitrogen (TAN). Ammonia flux also shows a nonlinear increase with increasing wind speed. Observed ammonia fluxes were generally lower in the cold season than in the warm season when lagoon temperatures are higher. About 41% of the equilibrium model predictions and 43% of the Coupled model predictions are found to be within a factor of two of the observed fluxes. Several model performance statistics were used to evaluate the performance of the two models against the observed flux data. These indicate that the simpler Equilibrium model does as well as the Coupled model. The possible effects of the “artificial” environment within the chamber, which is different from that in the ambient atmospheric conditions above the open lagoon surface, on the measured fluxes are also recognized.
Keywords: Ammonia flux; Coupled model; Equilibrium model; Mass transfer; Two-film transfer model;

Fine particle emission factors from vehicles in a highway tunnel: Effects of fleet composition and season by Andrew P. Grieshop; Eric M. Lipsky; Natalie J. Pekney; Satoshi Takahama; Allen L. Robinson (287-298).
In-use, fuel-based motor vehicle emission factors were determined using measurements made in a highway tunnel in Pittsburgh, Pennsylvania. Concentrations of PM2.5 mass, CO, CO2, and NO x were measured continuously. Filter-based measurements included PM2.5 mass, organic and elemental carbon (OC and EC), inorganic ions and metals. Fuel-based emission factors for each pollutant were calculated using a fuel-carbon balance. The weekday traffic volume and fleet composition varied in a consistent diurnal pattern with the estimated fraction of fuel consumed by heavy-duty diesel vehicle (HDDV) traffic ranging from 11% to 36%. The emission rate of most species showed a significant dependence on sample period. NO x , PM2.5, EC and OC emission factors were significantly larger during the early morning, truck-dominated period. Emissions of particulate metals associated with brake wear (Cu, Sb, Ba and potentially Ga) were emitted at higher rates during the rush-hour period, which is characterized by slower, stop-and-go traffic. Emission rates of crustal elements (Fe, Ca, Mg, Li), Zn and Mn were highest during the early-morning period when there was more heavy-truck traffic. A seasonal shift in average OC/EC ratio for the rush-hour period was observed; fall and summer OC/EC ratios are 1.0±0.6 and 0.26±0.06, respectively. Potential causes for this shift are increased partitioning of semi-volatile organic compounds into the gas phase during the summer months and/or effects of seasonal changes in fuel formulation. Emission factors for HDDV and light-duty vehicles (LDV) classes were estimated using a linear regression of emission factor as a function of fleet composition. The extrapolated emission factors generally agree with previously published measurements, though a substantial range in published values is noted.
Keywords: PM2.5; Organic carbon; Elemental carbon; Trace metals; Emission inventories;

Determination of levoglucosan in biomass combustion aerosol by high-performance anion-exchange chromatography with pulsed amperometric detection by Guenter Engling; Christian M. Carrico; Sonia M. Kreidenweis; Jeffrey L. Collett; Derek E. Day; William C. Malm; Emily Lincoln; Wei Min Hao; Yoshiteru Iinuma; Hartmut Herrmann (299-311).
Atmospheric particulate matter can be strongly affected by smoke from biomass combustion, including wildfires, prescribed burns, and residential wood burning. Molecular source tracer techniques help determine contributions of biomass smoke to particle concentrations if representative source profiles are available. Various wood smoke source profiles have been generated for residential wood burning; however, few emission data are available for the combustion of biomass under open-burning conditions. Anhydrosugars, produced as thermal degradation products of cellulose and hemicellulose, are typically analyzed by gas chromatography-mass spectrometry (GC-MS) after chemical derivatization. A simpler alternative analytical method, based on high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD), was developed here and utilized to measure several isomeric anhydrosugars (levoglucosan, mannosan, and galactosan) in primary smoke aerosol from various types of biomass and from different combustion conditions representative of prescribed and wildfires. Highly varying patterns were observed in the emission profiles of various molecular markers as a function of fuel type and combustion conditions. Emission factors of levoglucosan were a strong function of fuel type, combustion phase, and uphill versus downhill burn direction, varying from 36 to 1368 μg mg−1 organic carbon. Fuel type was the most important determinant, causing variations in emission factors of levoglucosan over an order of magnitude, while combustion phase and burn direction generally affected emission factors by a factor of 2–3. Mannosan and galactosan showed emission trends similar to levoglucosan. Levoglucosan emission factors from selected samples were compared to data obtained by two independent analytical methods, high-performance liquid chromatography (HPLC-MS) and GC-MS, showing rather good agreement. The HPAEC-PAD analytical method offers a simple alternative to GC-MS for future studies of aerosol concentrations of anhydrosugars, enabling more accurate estimates of contributions from biomass combustion to ambient particle concentrations.
Keywords: Levoglucosan; PM2.5; Aerosol; Smoke; Wildfire; IC-PAD; Emission factors;

The concentrations and sources of PM2.5 in metropolitan New York City by Youjun Qin; Eugene Kim; Philip K. Hopke (312-332).
The concentration time series of chemical species measured in PM2.5 samples from four speciation trend network (STN) sites in the New York City metropolitan area and a upwind background site were explored. PM2.5 concentrations and chemical compositions measured in metropolitan area of New York City are uniform. About 69–82% of PM2.5 mass derives from transport. The most important constituents of the PM2.5 were SO 4 2 - , NH4 and NO 3 - and account 54–67% of PM2.5 mass. More than 93% of SO 4 2 - and about 54–65% of NO 3 - are likely to have been transported into the NYC area based on the concentrations observed at the background site. Backward air parcel trajectories indicate that coal-fired power plants in the border area among West Virginia, Ohio and Pennsylvania are related to typical high PM2.5 events having peak secondary pollutant concentrations in New York City. Positive matrix factorization (PMF) was applied to identify the PM2.5 sources and estimate the source contributions. Sources common to all five sites included secondary sulfate, secondary nitrate, soil and aged sea salt. Oil combustion was identified at four of the sites. At the Elizabeth site, the oil combustion source appears to show an influence from ship emissions. Motor vehicles were apportioned into two sources (gasoline and diesel) at three site and three sources at the Elizabeth site, probably because of its proximity to a major interstate highway. At the Queens College site, only a combined motor vehicle factor could be resolved. The source profiles, source contributions and seasonal or weekday variations derived by PMF are compared to source inventories for the area. It appears that there were more vehicle exhausts and less dust and wood smoke than are indicated by the source inventories.
Keywords: PM2.5; Composition; Positive matrix factorization; PMF; Source apportionment; Emission inventory;

New York City (NYC) is presently in violation of the nation's PM2.5 annual mass standard, and will have to take actions to control the sources contributing to these violations. This paper seeks to differentiate the impact of long-range transported aerosols on the air quality of downtown NYC, so that the roles of local sources can more clearly be evaluated. Past source apportionment studies have considered single sites individually in their source apportionment analyses to identify and determine sources affecting that site, often finding secondary sulfates to be an important contributor, but not being able to quantify the portion that is transported vs. local. In this study, a rural site located in Sterling Forest, NY, which is near to the NYC area, but unaffected by local NYC sources, is instead used as a reference to separate the portion of the aerosol that is transported to our Manhattan, NYC site before conducting the source apportionment analysis. Sterling Forest is confirmed as a background site via elemental comparisons with NYC during regional transport episodes of Asian and Sahara sandstorm dusts, as well as by comparisons with a second background site in Chester, NJ. Two different approaches that incorporate Sterling Forest background data into the NYC source apportionment analysis are then applied to quantify local vs. transported aerosols. Six source categories are identified for NYC: regional transported sulfate, trans-continental desert dust, traffic, residual oil, “local” dust and World Trade Center fires pollution. Of these, the transported sulfates and trans-continental desert dust accounted for nearly half of the total PM2.5 mass in Manhattan during 2001, with more than half coming from these transported sources during the summer months. More than 90% of the Manhattan elemental carbon was found to be of local origins. Conversely, roughly 90% of the NYC sulfate mass was identified as transported into the city. Our results indicate that transported pollution has a major role in NYC's fine PM pollution. Reliably meeting the ambient PM2.5 air quality standards in New York will require that upwind sources, outside of the city, will also need to be controlled.
Keywords: New York City; PM speciation data; Source apportionment; Reference site; Long-range transported aerosols; Sulfates; Trans-continental desert dust;

Elemental composition of PM2.5 aerosols in Queens, New York: Evaluation of sources of fine-particle mass by Vincent A. Dutkiewicz; Sumizah Qureshi; Liaquat Husain; James J. Schwab; Kenneth L. Demerjian (347-359).
As a part of the PM2.5 Technology Assessment and Characterization Study-New York (PMTACS-NY) daily aerosol samples were collected from July 2001 to December 2004 at three NY sites: urban Queens, and rural Pinnacle State Park, and Whiteface Mountain lodge. Sulfate was determined on all samples while the 2001 and 2002 samples also had 15 metals determined: Mg, Al, Ca, V, Cr, Mn, Fe, Co, Ni, Zn, As, Se, Cd, Sb, and Pb. This is the second of a set of papers that deals with the composition of fine particulate matter at the urban site in Queens, NY. We use the large daily elemental database to explore the inter-elemental relationships with statistical methods and air trajectories on a seasonal basis to glean insight into the regional and local area sources impacting Metropolitan NY.
Keywords: Supesite; Particulate matter; Sulfate; Trace elements; PM2.5; Urban aerosols; Source emissions; Oil-fired emissions; Regional coal combustion; Air trajectories;

Positive matrix factorization (PMF) model was utilized along with wind direction and backward trajectory analyses, to identify and apportion local and regional sources to airborne PM2.5 in the metropolitan St. Louis, MO, area using data from the US Environmental Protection Agency's Speciation Trends Network. Local non-ferrous metal smelting and steel processing factors were identified by combining PMF contributions and wind direction analysis. Mobile (gasoline and diesel) sources were also resolved. Secondary sulfate and secondary nitrate factors appeared to have regional source origins that are located in the Ohio River Valley and the Midwestern agricultural farm lands, respectively. The transport of agriculturally emitted ammonia appears to be a major contributing factor to secondary nitrate formation in the Midwest. Impacts of African dust transport to the Midwestern PM2.5 were observed as well as transport of biomass burning aerosol from southern US area. This study presents an application of PMF and surface and upper air wind data to source identification of Midwestern fine aerosol.
Keywords: Positive matrix factorization; PM2.5; Wind direction; Backward trajectory; Source apportionment; Local and regional sources;

UNMIX modeling of ambient PM2.5 near an interstate highway in Cincinnati, OH, USA by Shaohua Hu; Rafael McDonald; Dainius Martuzevicius; Pratim Biswas; Sergey A. Grinshpun; Anna Kelley; Tiina Reponen; James Lockey; Grace LeMasters (378-395).
The “Cincinnati Childhood Allergy and Air Pollution Study (CCAAPS)” is underway to determine if infants who are exposed to diesel engine exhaust particles are at an increased risk for atopy and atopic respiratory disorders, and to determine if this effect is magnified in a genetically at risk population. In support of this study, a methodology has been developed to allocate local traffic source contributions to ambient PM2.5 in the Cincinnati airshed. As a first step towards this allocation, UNMIX was used to generate factors for ambient PM2.5 at two sites near at interstate highway. Procedures adopted to collect, analyze and prepare the data sets to run UNMIX are described. The factors attributed to traffic sources were similar for the two sites. These factors were also similar to locally measured truck engine-exhaust enriched ambient profiles. The temporal variation of the factors was analyzed with clear differences observed between factors attributed to traffic sources and combustion-related regional secondary sources.
Keywords: Source apportionment; Traffic sources; Diesel engine exhaust; Particles; Air pollution;

Source apportionment of Baltimore aerosol from combined size distribution and chemical composition data by David Ogulei; Philip K. Hopke; Liming Zhou; J. Patrick Pancras; Narayanan Nair; John M. Ondov (396-410).
Several multivariate data analysis methods have been applied to a combination of particle size and composition measurements made at the Baltimore Supersite. Partial least squares (PLS) was used to investigate the relationship (linearity) between number concentrations and the measured PM 2.5 mass concentrations of chemical species. The data were obtained at the Ponca Street site and consisted of six days’ measurements: 6, 7, 8, 18, 19 July, and 21 August 2002. The PLS analysis showed that the covariance between the data could be explained by 10 latent variables (LVs), but only the first four of these were sufficient to establish the linear relationship between the two data sets. More LVs could not make the model better. The four LVs were found to better explain the covariance between the large sized particles and the chemical species. A bilinear receptor model, PMF2, was then used to simultaneously analyze the size distribution and chemical composition data sets. The resolved sources were identified using information from number and mass contributions from each source (source profiles) as well as meteorological data. Twelve sources were identified: oil-fired power plant emissions, secondary nitrate I, local gasoline traffic, coal-fired power plant, secondary nitrate II, secondary sulfate, diesel emissions/bus maintenance, Quebec wildfire episode, nucleation, incinerator, airborne soil/road-way dust, and steel plant emissions. Local sources were mostly characterized by bi-modal number distributions. Regional sources were characterized by transport mode particles (0.2– 0.5 μ m ).
Keywords: Receptor modeling; Size distribution; PLS; Positive matrix factorization; PMF; Baltimore;

Identification of sources of atmospheric PM at the Pittsburgh Supersite, Part I: Single particle analysis and filter-based positive matrix factorization by Natalie J. Pekney; Cliff I. Davidson; Keith J. Bein; Anthony S. Wexler; Murray V. Johnston (411-423).
During the Pittsburgh Air Quality Study (PAQS), July 2001–September 2002, three co-located instruments analyzed the composition of ambient particulate matter (PM): (1) A single particle mass spectrometer, RSMS-3, was deployed to obtain high-temporal-resolution measurements of single particle size (>1.1 μm) and composition which were correlated with meteorological data to identify sources; (2) PM2.5 and PM10 were collected on cellulose filters using high-volume (hi-vol) samplers, followed by microwave-assisted digestion and analysis by inductively coupled plasma–mass spectrometry (ICP–MS). Positive matrix factorization (PMF) was used to identify possible source categories; and (3) a micro-orifice uniform-deposit impactor (MOUDI) obtained size-distributed samples of PM. Several days of MOUDI filters were selected for microwave-assisted digestion and analysis by ICP–MS.In this paper, sources identified using the single particle data were compared to the PMF results for the hi-vol/ICP–MS data. The strengths of each method were combined to hypothesize the most likely sources of various elements in ambient PM in Pittsburgh. In the final results, Mo and Cr are attributed to local specialty steel facilities; Fe, Mn, Zn, and K are attributed to a steel mill SE of the monitoring station; internally mixed Pb-containing particles are attributed to a major source to the NW; and Ga is attributed to coal combustion sources to the NW. There is a notable lack of oil combustion sources.The MOUDI data were used to resolve discrepancies between the single particle and hi-vol/ICP–MS data concerning the detection of Ti and Se. The hi-vol data showed appreciable Ti and Se masses, but RSMS-3 was unable to detect significant numbers of Ti-containing particles because of their large size, while we hypothesize that the volatility of Se caused it to be distributed more evenly over all emitted particles such that the amount of Se in any individual particle is below the limit of detection.
Keywords: Real-time single particle mass spectrometry; Positive matrix factorization; Ambient aerosols; Trace elements; Particle size–composition;

Identification of sources of atmospheric PM at the Pittsburgh Supersite—Part II: Quantitative comparisons of single particle, particle number, and particle mass measurements by Keith J. Bein; Yongjing Zhao; Natalie J. Pekney; Cliff I. Davidson; Murray V. Johnston; Anthony S. Wexler (424-444).
A single particle mass spectrometer, RSMS-3, and a MOUDI were deployed during the Pittsburgh Air Quality Study (PAQS), July 2001–September 2002, to obtain size resolved measurements of elemental composition for particulate matter (PM) within the Pittsburgh area. Elemental mass distributions from analysis of the MOUDI stages were directly compared to those constructed using the single particle data, in conjunction with coincident SMPS measurements, for specific days within the PAQS.Results from one episode on 27 October 2001 showed that approximately 80% of the metal containing particles detected on this day belonged to the Na/Si/K/Ca/Fe/Ga/Pb particle class. The density and shape factor of these particles were estimated to be 3.9±0.8 g/cc and 1.5±0.2, respectively, and the relative sensitivity factors for individual metals showed little variation with respect to particle diameter over the size range of 70–800 nm.Compared to the 27 October 2001 episode, there was a larger degree of variability in the metal containing particles detected during another episode on 14 March 2002. The Ca and Pb mass distributions from this day represent an ensemble of externally mixed particles. Estimates of particle density were provided for the dominant particle types, including EC/OC/Ca, Al/Si/Ca/Fe, EC/OC/Pb and Na/K/Zn/Pb, and estimates of particle shape factor were provided for the EC/OC/Ca and Na/K/Zn/Pb classes. Comparison with the 27 October 2001 Ca and Pb mass distributions revealed that the RSMS data reconstructed the MOUDI mass much better from the Ca/Pb containing particles detected on 14 March 2002 than those observed on 27 October 2001, suggesting that the single particle instrument sensitivity to both Ca and Pb depends on the particle matrix.
Keywords: Single particle mass spectrometry; Elemental mass distribution; Composition-resolved number distribution; Particle density; Particle shape factor; Pittsburgh Supersite experiment;

Four gas components (CO, SO2, HNO3 and NO y ) and PM2.5 (particulate matter ⩽2.5 μm in aerodynamic diameter) composition data including eight individual carbon fractions collected at four sites in Georgia and Alabama were analyzed with the positive matrix factorization (PMF) method. Multiple linear regression (MLR) was applied to regress the total PM mass against the estimated source contributions. The regression coefficients were used to scale the factor profiles. Nine factors were resolved at two urban sites (Atlanta, GA (JST) and Birmingham, AL (BHM)) and one rural site (Centerville, AL (CTR)). Eight factors were resolved at the other rural site (Yorkville, GA (YRK)). Six factors we refer to as soil, coal combustion/other, diesel emission, secondary sulfate, secondary nitrate, and wood smoke are common among the four sites. Two industry-related factors are similar at the two sites in the same state, but differ between states. Contrary to previous results using only PM2.5 data with non-speciated EC and OC data, diesel and gasoline emission factors were resolved at the two urban sites instead of only one single motor vehicle factor; diesel and gasoline factors were also resolved at the CTR site and a diesel factor was found at YRK instead of no motor vehicle factors at the two rural sites. The inclusion of gas components also improved the identification of the coal combustion/other factor among the four sites. This study shows that inclusion of gas phase data and temperature-resolved fractional carbon data can enhance the resolving power of source apportionment studies, especially for the factors we refer to as gas, diesel, and coal combustion/other.
Keywords: Thermal optical method; Carbon fraction; Positive matrix factorization; Source apportionment; Gas; Aerosol; Diesel; Gasoline;

Identification of sources and estimation of emission profiles from highly time-resolved pollutant measurements in Tampa, FL by Joseph Patrick Pancras; John M. Ondov; Noreen Poor; Matthew S. Landis; Robert K. Stevens (467-481).
Aerosol slurry samples were collected at 30-min intervals for sequential 1-month periods at each of two sites (Sydney and “Dairy”) in the Tampa Bay area during the 2002 Bay Regional Atmospheric Chemistry Experiment using the University of Maryland Semicontinuous Elements in Aerosol Sampler-II (SEAS-II). More than 500 samples, believed to be affected by plumes from local utility and industrial sources, were selected for electrothermal atomic absorption spectrophotometric analyses for elemental markers (Al, Fe, Cr, Cu, Mn, Pb, Se, As, Ni, Zn and Cd) based on excursions in SO2 and NO x measurements. Correlation of short-term excursions in metals and SO2, and surface wind directions observed between May 23 and 26th, 2002, revealed the influence of an animal feed supplements production facility (AFS), 17 km upwind at a station angle of 81°, for which emissions had not previously been detected by standard monitoring methods. Emission “profiles” for this source were developed, separately, from the time series data and by using principle components analysis (PCA) and positive matrix factorization (PMF). In addition, a local dust component was evident in Al and Fe concentration profiles during periods of elevated wind speeds and was resolved by PCA/PMF. Similarly, large but brief 1.5-h excursions in Zn (maximum, 403 ng m−3), Cd, and Pb on May 17th were correlated with winds from the direction of an incinerator (station angle, 250°) 17 km from Sydney. Lastly, large excursions in As concentrations (maximum, 86 ng m−3) observed (May 4th and 5th at Sydney and November 2nd and 3rd at the Dairy) were used to locate previously unrecognized sources, tentatively associated with combustion/production of pressure-treated lumber. Profiles developed directly from the time series data were in the range of those derived from PCA-PMF (AFS); and those for the incinerator, with previously published values.
Keywords: SEAS II; ETAAS; Time-resolved metals; PM1.2; BRACE;

Use of advanced receptor modelling for analysis of an intensive 5-week aerosol sampling campaign by Kathleen C. Buset; Greg J. Evans; W. Richard Leaitch; Jeffrey R. Brook; Desiree Toom-Sauntry (482-499).
This study investigates the application of the Multilinear Engine (ME) to a highly time-resolved aerosol concentration data set. Aerosol concentration, ambient gas and meteorological data were collected from 20 August to 25 September 2003 in Toronto, Ont., Canada. A suite of instruments was incorporated into the study, which produced a diverse air quality data set. The instrumentation included an aerosol mass spectrometer (AMS) that was used to analyse for non-refractory submicron particles and an aethelometer used to collect black carbon (BC) measurements, both at a time resolution of 15 min. A particles-into-liquid sampler coupled with an ion chromatrograph (PILS–IC) collected 15-min data on water-soluble inorganic aerosols during a portion of the total sampling period. The ME was applied to the AMS and aethelometer data, along with meteorological and time-of-day information. Five sources were identified: secondary sulphate characterized by high SO4 2− concentration and winds from the southwest; secondary nitrate characterized by high NO3 concentration and a significant diurnal trend with a peak in concentration during the morning; fresh organic (1) associated with BC and elevated concentration in the morning suggesting that this source was attributable to local vehicle traffic; fresh organic (2) which was not associated with a strong diurnal or wind direction trend; and aged organic aerosol which was associated with m / z = 44 , showed a multiday pattern of elevated concentration and was not strongly associated with any particular wind direction. This study also investigated the minimum number of days of 15-min time-resolved data which were required by the ME to produce meaningful source identification. It was determined that 6 days of data was the minimum required to produce source profile and temporal trends which were comparable to the ME results using the full sampling period.
Keywords: Ambient aerosol; High time resolution; Multilinear engine; Semi-continuous monitors; Source apportionment;

Scavenging wave propagation and influence distances for various gases absorbed by single liquid aerosols in the atmosphere are predicted to evaluate the effect of droplet–droplet interaction on transient mass transfer processes in clouds. Three greenhouse gases, CH4, N2O, and CO2, as well as five air pollutants, H2S, SO2, HCl, NH3, and HNO3, are taken into account. Considering the three greenhouse gases and the air pollutant H2S, because the driving forces of mass diffusion in the gas phase are by far smaller than those of the liquid phase, the gaseous scavenging behaviors in the vicinity of the droplets are absent. It thus reveals that the effect of mutual interaction of droplets on the absorption processes of these solutes is fairly slight. In regard to the other four air pollutants SO2, HCl, NH3, and HNO3, their mass diffusion numbers are relatively high, rendering that the scavenging waves in the gas phase are clearly observed in the initial uptake period. Increasing mass diffusion number makes the influence distance of the scavenging wave farther and the curvature effect along the droplet surface more pronounced. Consequently, it is recognized that the droplet–droplet interaction in clouds tends to decrease the absorption rate and elongate the uptake period as gases with large mass diffusion numbers are absorbed by droplets. In other words, the distance between cloud droplets will become an important parameter in determining the droplet absorption rate.
Keywords: Scavenging wave; Influence distance; Droplet absorption; Droplet–droplet interaction; Mass diffusion number;

Photochemical modeling, using the Comprehensive Air Quality Model with extensions (CAMx), was used to assess the impact of anthropogenic chlorine emissions on particulate matter formation, during a photochemical episode in southeast Texas from August to September 2000. Model performance was assessed by comparing observed and predicted hydrochloric acid, particle chloride, and particle sodium concentrations. The simulations indicated that anthropogenic chlorine emissions have the potential to enhance particulate matter formation by up to 9 μg m−3 in very localized areas during brief periods in the morning; at most times and at most locations, particulate chloride formation due to anthropogenic chlorine emissions was less than 0.1 μg m−3.
Keywords: Particulate matter; Chlorine chemistry; Particulate chloride;

Observational data, collected during a wood smoke episode in Houston, Texas, indicated that wood smoke mediated sulfate formation reactions, not accounted for in most current photochemical models, may have led to 5–10 μg m−3 of sulfate formation. A 3-D photochemical grid model was used to examine these heterogeneous/surface sulfate formation reactions on wood smoke particles. In the photochemical model, wood-smoke mediated sulfate formation was modeled by calculating the rate of impingement of SO2 molecules on the wood smoke particles, then assuming that a fraction of the impingements resulted in reaction. For reaction probabilities on the order of 0.01, the model predicted magnitudes, spatial distributions and temporal distributions of sulfate concentrations consistent with observations. Making the reaction probability dependent on oxidant availability did not change these overall findings. Observational data were not sufficiently detailed to be able to distinguish among the roles of different oxidants.
Keywords: Heterogeneous reaction; Sulfate formation; Wild fire emissions; PM modeling; TexAQS 2000;

Ammonia emissions, concentrations and implications for particulate matter formation in Houston, TX by R. Thomas Pavlovic; U. Nopmongcol; Y. Kimura; David T. Allen (538-551).
Seasonal average observational data, photochemical modeling analyses, and detailed observational data for a summer air pollution episode were used to assess the spatial and temporal distribution of ammonia-rich and ammonia poor conditions in southeast Texas. Seasonal average observational data and photochemical modeling analyses both suggest ammonia rich conditions throughout southeast Texas, but not enough ammonia present to create elevated concentrations of ammonium nitrate, except during morning hours. Analyses of ambient data available for the summer air pollution episode (which was also the modeled episode) indicate that ammonia-poor conditions may be more pervasive in southeast Texas during periods of intense photochemistry. Overall, the results of all three methods are consistent in suggesting that average ammonia availability in southeast Texas is comparable to the ammonia required to neutralize sulfate. Temporal and spatial variability in sulfate formation creates morning excesses of ammonia (leading to some morning nitrate formation) and ammonia poor conditions in SO2 plumes and during periods of high photochemical activity.
Keywords: Ammonium; Secondary particle formation; Sulfate; Nitrate;

Impacts of ozone precursor limitation and meteorological variables on ozone concentration in São Paulo, Brazil by Odón R. Sánchez-Ccoyllo; Rita Yuri Ynoue; Leila Droprinchinski Martins; Maria de Fátima Andrade (552-562).
Ozone concentrations in the heavily polluted metropolitan area of São Paulo (MASP), in Brazil, frequently exceed established international standards. This study aims to describe the impact that three meteorological variables (mixing height, wind speed and air temperature) on the ozone concentration, as well as reactive hydrocarbon (RHC) limitation and nitrogen oxide (NO x ) limitation, have on ozone formation in the area. To achieve these objectives the California Institute of Technology (CIT) Eulerian air quality model was applied combined with the same methodology described in Baertsch-Ritter et al. [2004. Atmospheric Chemistry and Physics 4, 423–438] In addition, NO x and RHC emission inventory reductions were used to evaluate their sensitivities in the CIT model. A simulation of an episode occurring in the MASP on 22 August 2000, when a peak ozone level of 127 ppbv was recorded, is presented. In the CIT model results for the base case, primary pollutant concentrations and ozone concentrations are in good agreement with the measured data. In addition, changes in mixing height, wind speed and air temperature input files have the greatest effect on peak ozone in the MASP, and the isolated effect of RHC emission inventory reduction leads to 26% lower ozone levels than in the base case. Based on the results of this study, we can conclude that with reduction of RHC emission could provide the best scenario for promoting lower ozone concentrations in the MASP.
Keywords: Photochemical model; Urban air pollution; Emission inventory; Meteorological sensitivity; RHC/NO x limitation;

Uncertainty in air quality model evaluation for particulate matter due to spatial variations in pollutant concentrations by Sun-Kyoung Park; Charles Evan Cobb; Katherine Wade; James Mulholland; Yongtao Hu; Armistead G. Russell (563-573).
Air quality model performance is usually evaluated by examining the relative agreement between volume-averaged simulations and point measurements, as volume-averaged measurements are seldom available. Because the two values have different spatial scales, accurate model evaluation is complicated by this mismatch in areas when the pollutant gradient is large. Uncertainty in the air quality model evaluation from the spatial variability of PM2.5 is quantitatively examined, and how much of model error might be explained by such variability is calculated. Added uncertainty of model performance is analyzed by comparing performance metrics between simulated concentrations and observations at one station between simulated levels and interpolated fields from observations. Normalized differences of the performance metrics (e.g., mean fractional error, MFE) calculated in these two ways indicate the uncertainty of the model performance due to spatial variation. Normalized difference of MFE for PM2.5 mass is approximately 17% in July 2001 and 15% in January 2002. To decrease the uncertainty, it has been suggested that observations be used only from spatially representative stations. When model performance is calculated with data from spatially representative stations, uncertainty decreased, and overall model performance improves. For example, MFE is seen to decrease up to 14% for PM2.5 mass and species concentrations, suggesting that up to 14% of MFE can be explained by the spatial variability of PM2.5. These results indicate that comparison between observed and simulated concentrations should not be used alone to assess performance of air quality models. Also, spatial variability should be considered in setting model performance goals.
Keywords: Model performance; Spatial variability; Representative stations;

Regional air quality simulations used for source apportionment must consider the role of boundary conditions on estimated species concentrations. This technical note, as part of the Big Bend Regional Aerosol and Visibility and Observational (BRAVO) Study, examines how sulfate concentrations simulated by the Regional Modeling System for Aerosols and Deposition (REMSAD) were influenced by two sets of sulfur boundary conditions: (1) spatially invariant lateral boundary conditions, in which sulfur levels were fixed in space on all four boundaries, and (2) boundary conditions derived from Georgia Tech/Goddard Global Ozone Chemistry Aerosol Radiation Transport Model (GOCART), resulting in sulfur levels that varied spatially. A series of REMSAD simulations were evaluated, and used to apportion sulfate compounds at Big Bend National Park (NP) in southwestern Texas. The spatially invariant boundary conditions specified sulfur dioxide and particulate sulfate mixing ratios near the surface at 200 and 280 ppt, respectively, and dropped to 50 and 70 ppt, respectively, at the highest model layer. The GOCART-derived boundary conditions, however, could be considerably higher or lower, e.g., sulfur dioxide mixing ratios ranging from 2000 ppt along the highly populated northeastern portion of the boundary to less than 10 ppt in the upper model layers. The introduction of the spatially varying GOCART sulfur mixing ratios resulted in a modest overall improvement in the ability of REMSAD to simulate regional sulfate concentrations (an improvement from 48% to 45% and 32% to 21% in normalized error and normalized bias, respectively). However, the sulfate source apportionment at Big Bend NP, a relatively remote area of North America, was significantly influenced, with the estimated contribution of boundary conditions to sulfate levels during the four-month study decreasing from 20% using the original boundary conditions to 7% using the GOCART-derived boundary conditions. This effect was even more pronounced during the 20% clearest days at Big Bend, with 25% of sulfate attributed to the spatially invariant boundary conditions vs. 10% of sulfate attributed to the GOCART-derived boundary conditions. These results do not represent a formal sensitivity study on the role of different boundary condition scenarios as year-specific, temporally varying concentrations were not available during the tightly scheduled BRAVO study. However, the results do indicate the benefits and necessity of incorporating global-scale models to specify boundary conditions in regional-scale air quality model simulations.
Keywords: REMSAD; GOCART; Boundary conditions; Sulfate; BRAVO;

Characterization and in vitro biological effects of concentrated particulate matter from Mexico City by A. De Vizcaya-Ruiz; M.E. Gutiérrez-Castillo; M. Uribe-Ramirez; M.E. Cebrián; V. Mugica-Alvarez; J. Sepúlveda; I. Rosas; E. Salinas; C. Garcia-Cuéllar; F. Martínez; E. Alfaro-Moreno; V. Torres-Flores; A. Osornio-Vargas; C. Sioutas; P.M. Fine; M. Singh; M.D. Geller; T. Kuhn; A.H. Miguel; A. Eiguren-Fernandez; R.H. Schiestl; R. Reliene; J. Froines (583-592).
Coarse and fine particles were collected using an ambient particle concentrator (VACES system) in the north, center and south regions of Mexico City during May and November of 2003 with the aim of collecting enough particulate matter (PM) to examine their chemical and physical characteristics, biological content, and toxicity potential. The chemical, morphological and biological composition of PM was determined, together with the redox activity, induction of apoptosis and DNA damage. Carbonaceous species determined by thermal-optical transmittance (TOT) showed that the highest concentrations were found in PM2.5 from the north and in PM10 from the center. When analyzed by inductively coupling plasma (ICP), levels of metals were higher in the coarse fraction, mainly in the north. Morphological analysis by Scanning Electron Microscope & Energy Dispersive X-ray Spectrometer (SEM-EDX) is shown. Bacteria, fungi and endotoxin were present mostly in the coarse samples from the north. Fine PM had higher redox activity, than the coarse PM assessed by the dithiothreitol (DTT) assay. Early apoptotic cell death assessed by annexin V was observed in A549 cells exposed to PM from all regions, particularly with those collected in May. The fine fraction from the south induced higher apoptotic cell death compared to the coarse fraction, in contrast, the coarse fraction from the north induced significantly higher apoptosis than the fine fraction. All PM samples induced DNA damage assessed by the comet assay on THP-1 cells when exposed to a concentration of 10 μg/mL, the highest DNA damage was produced by both particle fractions collected in the north in May and November. In conclusion, PM from the north showed a higher metal and biological content, apoptotic cell death induction and more extensive DNA damage. Also, fine PM fractions from all sampled regions showed more redox activity than the coarse fraction. In summary, location, season and size of PM collection influenced their chemical, morphological and biological composition and thus their toxicity to cells.
Keywords: Ambient particulate; Chemical composition; Dithiothreitol assay; Apoptosis; DNA damage; CAPs and in vitro;

In order to investigate the causes of visibility degradation in the metropolitan area of Seoul, extensive chemical and optical monitoring of aerosol was conducted at two urban sites; Junnong, Seoul and Yonghyun, Incheon during several seasonal intensive monitoring periods between August 2002 and August 2004. Light extinction, scattering, and absorption coefficients were measured simultaneously with a transmissometer, a nephelometer, and an aethalometer, respectively. Continuous aerosol chemical measurement was also made with Sunset elemental carbon/organic carbon (EC/OC) analyzers and on-line ion monitors. The mean light extinction budget for five major aerosol components; ammonium sulfate, ammonium nitrate, fine carbonaceous particles (EC and OC), fine soil, and coarse particle was estimated based on the measurement results. Investigation of the haze level revealed that PM2.5 mass concentrations at Junnong and Yonghyun measured under the Worst20% condition were approximately twice those of the Best20% condition. The worst visibility condition was well correlated with increases in mass concentrations of sulfate and nitrate, and EC particles. The mass concentration of aerosol components for the Worst20% was measured to be approximately two- to four-fold higher than those for the Best20%. Degree of visibility degradation was also analyzed based on the air mass pathway information obtained using the HYSPLIT model. Average light extinction coefficients under continental air flow condition at the Junnong and Yonghyun sites were the highest values of 704±414 and 773±546 Mm−1, respectively due to increased loading of fine particles. Visibility was greatly improved at both sites when atmosphere was impacted by air mass originated from Pacific Ocean.
Keywords: Visibility impairment; Light extinction budget; PM2.5; Aerosol chemistry;