Atmospheric Environment (v.44, #1)
Editorial board (i).
Methane emissions inventory verification in southern California by Ying-Kuang Hsu; Tony VanCuren; Seong Park; Chris Jakober; Jorn Herner; Michael FitzGibbon; Donald R. Blake; David D. Parrish (1-7).
Methane (CH4) and carbon monoxide (CO) mixing ratios were measured at an air quality monitoring station near the Mt. Wilson (MW) Observatory in southern California starting in the spring of 2007. Diurnal variation and mixing ratio correlation (R 2 = 0.81) were observed. The correlation results observed agree with previous aircraft measurements collected over the greater Los Angeles (LA) metropolitan area. The consistent agreement between CH4 and CO indicates these gases are well-mixed before reaching the sampling site and the emission source contributions of both compounds are reasonably constant. Since CH4 and CO are considered non-reactive on the time scale of dispersion within the LA urban area and their emission sources are likely to be similarly distributed (e.g., associated with human activities) they are subject to similar scales of atmospheric transport and dilution. This behavior allows the relationship of CH4 and CO to be applied for estimation of CH4 emissions using well-documented CO emissions. Applying this relationship a “top–down” CH4 inventory was calculated for LA County based on the measurements observed at MW and compared with the California Air Resources Board (CARB) “bottom–up” CH4 emissions inventory based on the Intergovernmental Panel on Climate Change recommended methodologies. The “top–down” CH4 emissions inventory is approximately one-third greater than CARB's “bottom–up” inventory for LA County. Considering the uncertainties in both methodologies, the different CH4 emissions inventory approaches are in good agreement, although some under and/or uninventoried CH4 sources may exist.
Keywords: Methane emissions; Greenhouse gas; Emission inventory; Inventory verification; Scaling ratio method;
Comparison of carcinogen, carbon monoxide, and ultrafine particle emissions from narghile waterpipe and cigarette smoking: Sidestream smoke measurements and assessment of second-hand smoke emission factors by Nancy Daher; Rawad Saleh; Ezzat Jaroudi; Hiba Sheheitli; Thérèse Badr; Elizabeth Sepetdjian; Mariam Al Rashidi; Najat Saliba; Alan Shihadeh (8-14).
The lack of scientific evidence on the constituents, properties, and health effects of second-hand waterpipe smoke has fueled controversy over whether public smoking bans should include the waterpipe. The purpose of this study was to investigate and compare emissions of ultrafine particles (UFP, <100 nm), carcinogenic polyaromatic hydrocarbons (PAH), volatile aldehydes, and carbon monoxide (CO) for cigarettes and narghile (shisha, hookah) waterpipes. These smoke constituents are associated with a variety of cancers, and heart and pulmonary diseases, and span the volatility range found in tobacco smoke.Sidestream cigarette and waterpipe smoke was captured and aged in a 1 m3 Teflon-coated chamber operating at 1.5 air changes per hour (ACH). The chamber was characterized for particle mass and number surface deposition rates. UFP and CO concentrations were measured online using a fast particle spectrometer (TSI 3090 Engine Exhaust Particle Sizer), and an indoor air quality monitor. Particulate PAH and gaseous volatile aldehydes were captured on glass fiber filters and DNPH-coated SPE cartridges, respectively, and analyzed off-line using GC–MS and HPLC–MS. PAH compounds quantified were the 5- and 6-ring compounds of the EPA priority list. Measured aldehydes consisted of formaldehyde, acetaldehyde, acrolein, methacrolein, and propionaldehyde.We found that a single waterpipe use session emits in the sidestream smoke approximately four times the carcinogenic PAH, four times the volatile aldehydes, and 30 times the CO of a single cigarette. Accounting for exhaled mainstream smoke, and given a habitual smoker smoking rate of 2 cigarettes per hour, during a typical one-hour waterpipe use session a waterpipe smoker likely generates ambient carcinogens and toxicants equivalent to 2–10 cigarette smokers, depending on the compound in question. There is therefore good reason to include waterpipe tobacco smoking in public smoking bans.
Keywords: Environmental tobacco smoke; Aerosol dynamics; Environmental chamber; Shisha; Hookah;
Compositional characterization of PM2.5 emitted from in-use diesel vehicles by Nguyen Thi Kim Oanh; Worrarat Thiansathit; Tami C. Bond; R. Subramanian; Ekbordin Winijkul; Ittipol Paw-armart (15-22).
In Asian developing countries diesel vehicles contribute significantly to urban air pollution. The emission factors (EF) and exhaust gas composition of these vehicles may be different from those in the US and Europe, where most emission measurements are taken. This study focuses on the fine particulate matter (PM2.5) emission from in-use diesel vehicles in Bangkok, with the goal of providing EF and source profiles that are more appropriate for developing countries. The chassis dynamometer test results for 93 vehicles, including 39 light duty (LD) and 54 heavy duty (HD) of the age models between 1972 and 2005, are presented. PM EF are lower for vehicles of newer year models, consistent with the implementation of engine standards. The average PM2.5 EF of 0.23 g km−1 for LD, and 1.76 g km−1 for HD trucks and buses are generally higher than the literature reported values. Old HD trucks produce the highest PM EF of above 3 g km−1. Black carbon (BC), measured by an optical method, is well correlated with elemental carbon (EC) by TOT, but is consistently about 1.7 times higher. Between the LD and HD fleets, there is no significant difference in the fractional composition (BC, EC, OC, water soluble ions and elements) of emitted PM2.5. The composite source profile, weighted against the fleet composition and the vehicle km travelled (VKT) for the city has an average OC of 19%, EC of 47%, and sulfate of 2%, which are close to those reported for 1980s US diesel vehicles.
Keywords: Diesel particles; Emission factor; Composition; Composite diesel PM2.5 profile; Bangkok;
Observation of the primary NO2 and NO oxidation near the trunk road in Tokyo by Hiroaki Minoura; Akiyoshi Ito (23-29).
By the reinforcement of the vehicle emission reduction requirement in Japan, the nitrogen oxides (NOx) concentration in a roadside atmosphere decreased clearly recently. However, the ambient nitrogen dioxide (NO2) concentration does not show a substantial decrease.For the forecast of the improvement of the roadside NO2 by the motor vehicle emission regulation, we have been developing a roadside air quality simulation model. The chemical reactions of nitrogen oxide (NO) oxidation with ozone (O3), photodissociation of NO2, and O3 formation were included in this model. This study was carried out to clarify the NO2 behavior near roadside. Involving a spatial distribution of O3 concentration measurement, temporal and spatial variation of NO and NO2 was measured by the devices of chemiluminescence method which were prepared for each species. Concentration change was measured at the same time in four sites every 1 s to pay attention to a percentage of NO2/NOx which varied from route neighborhood to lee side way. The air flow of each sites was monitored by the ultrasonic 3D anemometer. The effect of NO2 concentration change due to the air stagnation or background ozone concentration was evaluated.From the cycle variation of potential ozone (PO) concentration as a function of the elapsed time of the traffic signal, the direct exhaust NO2 was estimated, and, around Noge intersection of Ring 8, Tokyo, 7.3% was obtained as primary NO2 fraction from vehicles. During an advection from the curbside site (0 m) to the 20 m remote site, more than 40% of NO oxidized and generate NO2 at 10 m height. At 3 m height, 7% of NO2 was generated and O3 was consumed in same quantity at the same time.
Keywords: Nitric oxide; Nitrogen dioxide; Ozone; Roadside air quality; Vehicle emission; Real-time measurement;
Trends of primary and secondary pollutant concentrations in Finland in 1994–2007 by Pia Anttila; Juha-Pekka Tuovinen (30-41).
The trends in the atmospheric concentrations of the main gaseous and particulate pollutants in urban, industrial and rural environments across Finland were estimated for the period of 1994–2007. The statistical analysis was based on generalized least-squares regression with classical decomposition and autoregressive moving average (ARMA) errors, which was applied to monthly-averaged data. In addition, three alternative methods were tested. Altogether 102 pollutant time series from 42 sites were analyzed. During the study period, the concentrations of SO2, CO and NOx declined considerably and widely across Finland. The SO2 concentrations at urban and industrial sites were approaching background levels. The reductions in NOx and CO concentrations were comparable to those in national road traffic emissions. A downward trend was detected in half of the NO2 time series studied, but the reductions were not as large as would be expected on the basis of emission trends, or from NOx concentrations. For O3, neither the mean nor peak values showed large changes in background areas, but were increasing in the urban data. For PM10, five of the 12 urban time series showed decreasing mean levels. However, the highest concentrations, typically attributable to the problematic springtime street dust, did not decrease as widely. The reduction of the long-range transported major ions, mainly driven by the large-scale reduction in sulphur emissions, possibly plays a significant part in the decreases in the mean PM10 concentrations. It was shown that the handling of the serially-correlated data with the ARMA processes improved the analysis of monthly values. The use of monthly rather than annually-averaged data helped to identify the weakest trends.
Keywords: Long-term trend; Air quality monitoring; Generalized least-squares (GLS) regression; Autoregressive moving average (ARMA) errors;
Analysis of urban pollution episodes by inverse modeling by Hector Jorquera; Julio Castro (42-54).
Urban pollution episodes pose two relevant issues: a) was the episode controlled by specific meteorology, a rise of emissions or both? b) Were mitigation measures effective in curbing down pollution? A methodology for answering those questions comes from an inverse modeling approach. In this work we have applied the methodology to the city of Santiago, Chile for which the required input data are available. We use a Kalman filter and ambient observations to constrain sources of tracers such as CO, elemental carbon and suspended street dust. The period analyzed is the week from May 20th till May 26th 2005. We find that a posteriori CO emissions were 76% of the a priori estimates. For suspended street dust a posteriori values are 36% and 21% of the prior values for coarse and fine fractions, respectively. Elemental carbon emissions are underestimated in the prior inventory – we find a correction factor of 1.53 for the whole week. Sensitivity analyses tested the robustness of a posteriori estimates, generating ensembles of simulations for different modeling options. For different initial prior estimates, the ratio of standard deviation to mean values was below 0.20 for 75% of the a posteriori, estimated emissions. For different choices of the error covariance matrices and model errors those ratios were below 0.30 for 75% of a posteriori emissions, which shows the robustness of results for different parameter choices – only a small fraction of results were not significant. The high pollution peaks on May 21st are due to specific meteorological conditions and increased traffic emissions as well. Contingency measures taken on Sunday May 22nd and better dispersion conditions on Monday May 23rd stopped the accumulation of those pollutants, showing the effectiveness of short term strategies such as traffic bans and street sweeping operations in curbing down traffic pollution at Santiago.
Keywords: Inverse modeling; Emission inventory; Santiago de Chile; Kalman filter; Urban air quality;
Experimental investigation of particulate emissions from a diesel engine fueled with ultralow-sulfur diesel fuel blended with diglyme by Yage Di; C.S. Cheung; Zuohua Huang (55-63).
Experiments are conducted on a 4-cylinder direct-injection diesel engine using ultralow-sulfur diesel as the base fuel and diglyme as the oxygenate component to investigate the particulate emissions of the engine under five engine loads at two engine speeds of 1800 rev min−1 and 2400 rev min−1. Blended fuels containing 5%, 10.1%, 15.2%, 20.4%, 25.7% and 53% by volume of diglyme, corresponding to 2%, 4%, 6%, 8%, 10% and 20% by mass of oxygen, are studied. The study shows that with the increase of oxygen in the fuel blends, smoke opacity, particulate mass concentration, NOx concentration and brake specific particulate emission are reduced at the two engine speeds. However, the proportion of soluble organic fraction is increased. For each blended fuel, the total particle number concentration is higher while the geometric mean diameter is smaller, compared with that of ultralow-sulfur diesel, though the particle number decreases with the oxygen content of the blended fuel. Furthermore, the blended fuels also increase the number concentrations of particles smaller than 100 nm.
Keywords: Diglyme; Ultralow-sulfur diesel; Particulate mass concentration; Particle size distribution; Trade-off;
A comparison of trajectory and air mass approaches to examine ozone variability by Robert E. Davis; Caroline P. Normile; Luke Sitka; David M. Hondula; David B. Knight; Stephen P. Gawtry; Philip J. Stenger (64-74).
Back trajectory analysis is a commonly-used tool for understanding how short-term variability in surface ozone depends on transport into a given location. Lesser-used but equally effective methods are air-mass based approaches that are primarily driven by changes in temperature and humidity conditions. We compare and combine these two fundamentally different approaches by evaluating daily near-surface afternoon warm-season ozone concentrations from 2001 to 2006 in and around the Shenandoah Valley of Virginia. Analysis of variance is used to compare summer afternoon ozone levels between air masses as identified by the Spatial Synoptic Classification to clusters of 72-h back trajectories estimated by the HYSPLIT model.Ozone concentrations vary significantly across both air masses and trajectory clusters at all ozone monitors. Concentrations are highest for air masses characterized by dry, warm conditions and for air originating from the north and west of the study area or circulating over the mid-Atlantic region. In many cases, the interaction between synoptic types and back trajectory clusters produce results not evident from the examination of simple trajectories or air masses alone. For example, ozone concentrations on Moist Moderate days are 30 ppb higher when air parcels travel moderate distances into the Shenandoah Valley from the west than when they travel longer distances from the north or northeast. Combining air mass and trajectory approaches provides a more useful characterization of air quality conditions than either method alone.
Keywords: Tropospheric ozone; Air mass; Back trajectory; Synoptic climatology; Shenandoah Valley; Virginia;
The assessment of the presence and main constituents of particulate matter ten microns (PM10) in Irish, rural and urban air by Tony Byrd; Mary Stack; Ambrose Furey (75-87).
This work summarizes the results of a series of comprehensive studies on particulate matter (PM10) carried out in County Cork, Ireland from 2005 to 2006. Monitoring sites were selected in accordance with different climatic and geographic conditions as well as anthropogenic influences, varying from rural background to industrial sites. Measurements were carried out with gravimetric high-volume samplers coupled with validated elemental analyses using Inductively Coupled Plasma-Optical Emission Spectroscopy, ion chromatography and flow injection analysis.Mean daily values, chemical compositions and source apportionment analyses were obtained and discussed as a function of the diverse monitoring sites and varying climatic episodes. High PM10 episodes are recorded during continental air mass impacts on Ireland, with a 50% increase in particulate concentration from the average values recorded in 2005. Chemical specification data, carried out by Principle Component Analysis (PCA) shows an increase in the crustal mineral load for most of the study sites. Furthermore, a high marine aerosol load is evident in coastal and urban study sites.The daily mean PM10 levels of 34 μg m−3 for an industrial region and 20 μg m−3 for coastal – rural site, with the urban site recording 14 μg m−3 are indicative of the Irish atmospheric air quality (allowing for local variations and weather). The natural background contribution in this region is estimated to be 3 μg m−3. The contribution from natural re-suspension and marine aerosol measured in this study can account for up to 56% of the 2010 EU annual limit value (20 μg m−3 PM10) under directive European Community (1999/30/EC). This contribution will account for up to 28% of the revised annual limit (40 μg m−3 PM10) under directive (2008/50/EC).The study demonstrates, that it could be challenging for a country such as Ireland whose national air pollution levels are low, as well as for other EU member states to meet the air quality limit in directive European Community (1999/30/EC).
Keywords: PM10; Ireland; Atmospheric aerosol and elemental composition; Maritime influence; Principle component analysis (PCA);
Observations of nucleation-mode particle events and size distributions at a rural New England site by Philip F. Place; Luke D. Ziemba; Robert J. Griffin (88-94).
Particle number (PN) concentrations, size distributions, and composition were measured continuously at the University of New Hampshire atmospheric observatory at Thompson Farm from 9 February to 4 April, 2007. A total of thirteen PN events, identified by PN concentration statistics, were observed during this two-month period. Events were subdivided into five different event types based on event duration and secondary measurements. Four of the five event types were observed, with the majority of events consisting of long-lived episodes, greater than 5 h in duration, associated with air mass backward trajectories from the clean northwest. Particle size distributions indicated increased number concentrations of nucleation-mode particles during event periods and particle growth of the nucleation-mode fraction. Particle diameter growth rates, determined from the geometric mean diameter of the 6–60 nm particle fraction, ranged between 0.9 and 5.5 nm h−1. All events displayed steady particle growth rates, indicating the regional nature of PN events. An Aerodyne quadrupole Aerosol Mass Spectrometer indicated that pre-existing aerosol concentrations were decreased on PN event days (compared to non-event days), as were temperature and absolute humidity; in contrast, solar radiation was increased on event days. Finally, theoretical particle growth rates from oxidation products of SO2, toluene, isoprene, and α-pinene were calculated and compared to measured growth rates. These species were able to account for up to 42.4% of the observed growth.
Keywords: AIRMAP; Particle growth; SMPS; Thompson Farm; Nucleation parameter;
PMF analysis of impacts of SO2 from Miyakejima and Asian Continent on precipitation sulfate in Japan by Kyo Kitayama; Naoto Murao; Hiroshi Hara (95-105).
PMF and back-trajectory analyses successfully evaluated contributions of sulfur dioxide to precipitation chemistry in Japan in terms of two major emission sources, Miyakejima and the Asian Continent. Precipitation chemistry datasets of Japanese Acid Deposition Survey (JADS) were subjected to PMF analysis to obtain the calculated concentration with contributions of five factors. The major sources were discussed for four selected JADS sites: Tanzawa, Tsukuba, Echizen and Goto. The first two are located close to Miyakejima, a volcano starting to erupt in 2000, while the others are located close to the Asian Continent on a national scale. PMF analysis of the observations suggested five factors, Factors 1–5, which corresponded to different acids and salts: Factor 1; H2SO4, Factor 2; HNO3 and NH4NO3, Factor 3; (NH4)2SO4 and NH4NO3, Factor 4; CaSO4 and CaNO3, and Factor 5; NaCl and MgCl2. Concentration changes associated with the eruption of Miyakejima and the seasonal airflow were discussed in term of Factors 1–5. At Tanzawa and Tsukuba, the monthly mean concentration of Factor 1 remarkably changed after the onset of the eruption, although the concentrations of the other factors remained unchanged. This change suggested the volcanic SO2 would be responsible for the Factor 1 concentration. No particular seasonality was confirmed for these sites. On the other hand, the volcanic impact did not appear to extend to Echizen and Goto because no apparent increases were detected in association with the eruption. However, remarkably seasonal changes were clearly detected for these sites, where winter concentration of SO4 2− was two to four times larger than summer ones. This seasonal change was attributable to the northwesterly monsoon in winter which will transport SO2 and SO4 2− from the continental sources and the sea salt SO4 2− from East China Sea and Sea of Japan, which was supported by back-trajectory analysis.
Keywords: Positive matrix factorization; Precipitation chemistry; Sulfate; Miyakejima; Japan;
Determination of background concentrations for air quality models using spectral analysis and filtering of monitoring data by O. Tchepel; A.M. Costa; H. Martins; J. Ferreira; A. Monteiro; A.I. Miranda; C. Borrego (106-114).
The use of background concentrations in air pollution modelling is usually a critical issue and a source of errors. The current work proposes an approach for the estimation of background concentrations using air quality measured data decomposed on baseline and short-term components. For this purpose, the spectral density was obtained for air quality monitoring data based on the Fourier series analysis. After, short-term fluctuations associated with the influence of local emissions and dispersion conditions were extracted from the original measurements using an iterative moving-average filter and taking into account the contribution of higher frequencies determined from the spectral analysis. The deterministic component obtained by the filtering is characterised by wider spatial and temporal representativeness than original monitoring data and is assumed to be appropriate for establishing the background values.This methodology was applied to define background concentrations of particulate matter (PM10) used as input data for a local scale CFD model, and compared with an alternative approach using background concentrations provided by a mesoscale air quality modelling system. The study is focused on a selected domain within the Lisbon urban area (Portugal). The results present a better performance for the microscale model when initialised by decomposed time series and demonstrate the importance of the proposed methodology in reducing the uncertainty of the model predictions.The decomposition of air quality measurements and the removal of short-term fluctuations discussed in the work is a valuable technique to determine representative background concentrations.
Keywords: Spectral analysis; Time series decomposition; Urban air quality; Road traffic pollution; Air quality modelling uncertainty;
The effect of marine isoprene emissions on secondary organic aerosol and ozone formation in the coastal United States by Brett Gantt; Nicholas Meskhidze; Yang Zhang; Jun Xu (115-121).
The impact of marine isoprene emissions on summertime surface concentrations of isoprene, secondary organic aerosols (SOA), and ozone (O3) in the coastal areas of the continental United States is studied using the U.S. Environmental Protection Agency regional-scale Community Multiscale Air Quality (CMAQ) modeling system. Marine isoprene emission rates are based on the following five parameters: laboratory measurements of isoprene production from phytoplankton under a range of light conditions, remotely-sensed chlorophyll-a concentration ([Chl–a]), incoming solar radiation, surface wind speed, and sea-water optical properties. Model simulations show that marine isoprene emissions are sensitive to meteorology and ocean ecosystem productivity, with the highest rates simulated over the Gulf of Mexico. Simulated offshore surface layer marine isoprene concentration is less than 10 ppt and significantly dwarfed by terrestrial emissions over the continental United States. With the isoprene reactions included in this study, the average contribution of marine isoprene to SOA and O3 concentrations is predicted to be small, up to 0.004 μg m−3 for SOA and 0.2 ppb for O3 in coastal urban areas. The light-sensitivity of isoprene production from phytoplankton results in a midday maximum for marine isoprene emissions and a corresponding daytime increase in isoprene and O3 concentrations in coastal locations. The potential impact of the daily variability in [Chl-a] on O3 and SOA concentrations is simulated in a sensitivity study with [Chl-a] increased and decreased by a factor of five. Our results indicate that marine emissions of isoprene cause minor changes to coastal SOA and O3 concentrations. Comparison of model simulations with few available measurements shows that the model underestimates marine boundary layer isoprene concentration. This underestimation is likely due to the limitations in current treatment of marine isoprene emission and a coarse spatial resolution used in the model simulations.
Keywords: Marine isoprene; Secondary organic aerosol; Ozone; CMAQ;
Solvent extracted organic matter and polycyclic aromatic hydrocarbons distributed in size-segregated airborne particles in a zone of México City: Seasonal behavior and human exposure by Omar Amador-Muñoz; Rafael Villalobos-Pietrini; Ma. Cristina Agapito-Nadales; Zenaida Munive-Colín; Leonel Hernández-Mena; Magdalena Sánchez-Sandoval; Sandra Gómez-Arroyo; José Luis Bravo-Cabrera; Judith Guzmán-Rincón (122-130).
Airborne particulate mass was collected in a cascade impactor, and the mass concentration of solvent extracted organic matter (SEOM) and polycyclic aromatic hydrocarbons (PAH) were determined. A greater mass concentration of particles, SEOM and PAH were obtained in the dry season than in the rainy season for all impact stages; however, in the rainy season the proportion of SEOM/particles mass increased for all stages. There was an average decrease in particle mass concentration of 52.1 ± 6.7%, a 33.6 ± 12.3% decrease in SEOM and a 43.9 ± 16.9% decrease in heavy PAH (≥228 g mol−1) in the rainy season. Heavy PAH were distributed in fine particles, while light PAH were more abundant in coarse particles. Estimations of SEOM and PAH inhaled daily by a person were made. Considering the carcinogenic PAH median mass (10th–90th percentiles) in 20 m3 of air, and the sum of all stages that could be inhaled daily by a person, estimates of 137 ng day−1 (74–246) in the dry season and 57 ng day−1 (21–101) in the rainy season were determined. The toxic equivalent factors were calculated to more accurately characterize the carcinogenic properties of PAH mixtures. This was based on the contribution of the carcinogenic potency of benzo[a]pyrene. These estimations would need to be considered in establishing standards for Mexican air quality. Correlations were shown between other atmospheric pollutants and masses of particles, SEOM and PAH. Vehicles were suggested as an emission source for SEOM and PAH.
Keywords: Airborne particles; Organic matter; Polycyclic aromatic hydrocarbons; Toxic equivalent factors; Mexico City;
Highly time- and size-resolved characterization of submicron aerosol particles in Beijing using an Aerodyne Aerosol Mass Spectrometer by Junying Sun; Qi Zhang; Manjula R. Canagaratna; Yangmei Zhang; Nga L. Ng; Yele Sun; John T. Jayne; Xiaochun Zhang; Xiaoye Zhang; Douglas R. Worsnop (131-140).
Atmospheric aerosols are a major pollutant in Beijing—a megacity in China. To achieve a better understanding of the characteristics, sources and processes of aerosols in Beijing, an Aerodyne Aerosol Mass Spectrometer (AMS) was deployed at an urban site in July 2006 to obtain size-resolved chemical composition of non-refractory submicron particles (NR-PM1) at 5 min resolution. During this study, NR-PM1 was on average composed of 25% sulfate, 22% nitrate, 16% ammonium, 1.4% chloride and 35% of organic aerosol (OA) species. The average size distributions of sulfate, nitrate and ammonium were very similar and characterized by a prominent accumulation mode peaking at Dva ≈ 600 nm. The average size distribution of OA was significantly broader due to the presence of an ultrafine mode. Multivariate analysis of the AMS organic spectra with Positive Matrix Factorization (PMF) identified a hydrocarbon-like OA (HOA) and two oxygenated OA (OOA) components. The HOA component likely corresponded to primary OA material associated with combustion-related emissions. The two OOA components, which likely corresponded to more oxidized (OOA I) and less oxidized (OOA II) secondary OA materials, accounted for 45 ± 16% and 16 ± 7.2%, respectively, of the observed OA mass. OOA I correlated well with sulfate while OOA II correlated well with nitrate. The particle loading, composition and size distributions observed during this campaign were highly variable. Backtrajectory analysis indicates that this variability correlated with the varying impacts of regional and local sources and processes.
Keywords: Fine particles; Primary Organic Aerosol (POA); Secondary Organic Aerosol (SOA); Megacity; Air pollution; Size distribution; Aerosol sources and processes;