Mapping the spatial distribution of primary and secondary PM2.5 in a multi-industrial city by combining monitoring and modeling results

Industrial cities are strongly influenced by primary emissions of PM2.5 from local industries. In addition, gaseous precursors, such as sulfur oxides (SOX), nitrogen oxides (NOX), and volatile organic compounds (VOCs), emitted from industrial sources, undergo conversion into secondary inorganic and organic aerosols (SIAs and SOAs). In this study, the spatial distributions of primary and secondary PM2.5 in Ulsan, the largest industrial city in South Korea, were visualized. PM2.5 components (ions, carbons, and metals) and PM2.5 precursors (SO2, NO2, NH3, and VOCs) were measured to estimate the concentrations of secondary inorganic ions (SO42-, NO3-, and NH4+) and secondary organic aerosol formation potential (SOAFP). The spatial distributions of SIAs and SOAs were then plotted by combining atmospheric dispersion modeling, receptor modeling, and monitoring data. Spatial distribution maps of primary and secondary PM2.5 provide fundamental insights for formulating management policies in different districts of Ulsan. For instance, among the five districts in Ulsan, Nam-gu exhibited the highest levels of primary PM2.5 and secondary nitrate. Consequently, controlling both PM2.5 and NO2 emissions becomes essential in this district. The methodology developed in this study successfully identified areas with dominant contributions from both primary emissions and secondary formation. This approach can be further applied to prioritize control measures during periods of elevated PM levels in other industrial cities.

Contribution of Physical and Chemical Properties to Dithiothreitol-Measured Oxidative Potentials of Atmospheric Aerosol Particles at Urban and Rural Sites in Japan

Dithiothreitol-measured oxidative potential (OPDTT) can chemically quantify the adverse health effects of atmospheric aerosols. Some chemical species are characterized with DTT activities, and the particle diameter and surface area control DTT oxidizability; however, the physical contribution to OPDTT by atmospheric aerosols is controversial. Therefore, we performed field observations and aerosol sampling at urban and rural sites in Japan to investigate the effect of both physical and chemical properties on the variation in OPDTT of atmospheric aerosols. The shifting degree of the representative diameter to the ultrafine range (i.e., the predominance degree of ultrafine particles) was retrieved from the ratio between the lung-deposited surface area and mass concentrations. The chemical components and OPDTT were also elucidated. We discerned strong positive correlations of K, Mn, Pb, NH4+, SO42−, and pyrolyzable organic carbon with OPDTT. Hence, anthropogenic combustion, the iron–steel industry, and secondary organic aerosols were the major emission sources governing OPDTT variations. The increased specific surface area did not lead to the increase in the OPDTT of atmospheric aerosols, despite the existing relevance of the surface area of water-insoluble particles to DTT oxidizability. Overall, the OPDTT of atmospheric aerosols can be estimated by the mass of chemical components related to OPDTT variation, owing to numerous factors controlling DTT oxidizability (e.g., strong contribution of water-soluble particles). Our findings can be used to estimate OPDTT via several physicochemical parameters without its direct measurement.

A review of aerosol chemistry in Asia: insights from aerosol mass spectrometer measurements

Anthropogenic emissions in Asia have significantly increased during the last two decades; as a result, the induced air pollution and its influences on radiative forcing and public health are becoming increasingly prominent. The Aerodyne Aerosol Mass Spectrometer (AMS) has been widely deployed in Asia for real-time characterization of aerosol chemistry. In this paper, we review the AMS measurements in Asia, mainly in China, Korea, Japan, and India since 2001 and summarize the key results and findings. The mass concentrations of non-refractory submicron aerosol species (NR-PM₁) showed large spatial distributions with high mass loadings occurring in India and north and northwest China (60.2-81.3 μg m^-3), whereas much lower values were observed in Korea, Japan, Singapore and regional background sites (7.5-15.1 μg m^-3). Aerosol composition varied largely in different regions, but was overall dominated by organic aerosols (OA, 32-75%), especially in south and southeast Asia due to the impact of biomass burning. While sulfate and nitrate showed comparable contributions in urban and suburban regions in north China, sulfate dominated inorganic aerosols in south China, Japan and regional background sites. Positive matrix factorization analysis identified multiple OA factors from different sources and processes in different atmospheric environments, e.g., biomass burning OA in south and southeast Asia and agricultural seasons in China, cooking OA in urban areas, and coal combustion in north China. However, secondary OA (SOA) was a ubiquitous and dominant aerosol component in all regions, accounting for 43-78% of OA. The formation of different SOA subtypes associated with photochemical production or aqueous-phase/fog processing was widely investigated. The roles of primary emissions, secondary production, regional transport, and meteorology on severe haze episodes, and different chemical responses of primary and secondary aerosol species to source emission changes and meteorology were also demonstrated. Finally, future prospects of AMS studies on long-term and aircraft measurements, water-soluble OA, the link of OA volatility, oxidation levels, and phase state were discussed.

Consumption of Hydrocarbons and Its Relationship with Ozone Formation in Two Chinese Megacities

Continuous measurements of ozone and its precursors were performed at sites in two Chinese megacities, i.e., an urban site in Beijing and a suburban site in the Pearl River Delta (PRD). At both sites, the total oxidants (O3 + NO2) varied with the ratio of ethylbenzene to m,p-xylenes, which serves as an indicator of photochemical aging. An observation-based method (OBM) was derived for calculating the photochemical consumption of individual non-methane hydrocarbons (NMHCs) based on the observed NMHC concentrations and the ratio of ethylbenzene to m,p-xylenes. The results show a strong correlation between the oxidant level and the derived consumption of precursors at the two sites (R2 = 0.81 for the PRD site and R2 = 0.83 for the Beijing site), demonstrating a strong cause–effect relationship. The relative “consumption efficiency” among NMHCs was calculated based on the integrated amount of hydroxyl radicals derived from the ratio of ethylbenzene to xylenes. Thus, the percent contributions to ozone formation from each individual NMHC can be calculated. This concept of consumption is purely observation-based and provides an easy way to bypass complicated modeling and the necessity of knowing instantaneous concentrations of hydroxyl radicals, which are highly illusive in nature.

Seasonal and Annual Source Appointment of Carbonaceous Ultrafine Particulate Matter (PM0.1) in Polluted California Cities

Samples of ultrafine particle matter mass (PM_0.1) were collected over 12 months at three cities in California: Los Angeles, East Oakland, San Pablo, and over six months at Fresno. Molecular markers adjusted for volatility and reactivity were used to calculate PM_0.1 source contributions. Wood burning was a significant source of PM_0.1 organic carbon (OC) during the winter months in northern California (17-47%) but made smaller contributions in other months (0-8%) and was minor in all seasons in Los Angeles (0-5%), except December (17%) during holiday celebrations. Meat cooking was the largest source of PM_0.1 OC across all sites (13-29%), followed by gasoline combustion (7-21%). Motor oil and diesel fuel combustion made smaller contributions to PM_0.1 OC (3-10% and 3-7%, respectively). Unresolved sources accounted for 22-56% of the PM_0.1 OC. The lack of a clear seasonal profile for this unresolved OC suggests that it may be a primary source rather than secondary organic aerosol (SOA). PM_0.1 elemental carbon (EC) was dominated by diesel fuel combustion with less than 15% contribution from other sources. All sources besides wood smoke exhibited relatively constant seasonal source contributions to PM_0.1 OC reflecting approximately constant emissions over the annual cycle. Annual-average source contributions to PM_0.1 OC calculated with traditional molecular markers were similar to the source contributions calculated with the modified molecular markers that account for volatility and reactivity.

Characterization of PM2.5 and identification of transported secondary and biomass burning contribution in Seoul, Korea

The chemical and seasonal characteristics of fine particulates in Seoul, Korea, were investigated based on 24-h integrated PM_2.5 measurements made over four 1-month periods in each season between October 2012 and September 2013. The four-season average concentration of PM_2.5 was 37 μg m^-3, and the major chemical components were secondary inorganic aerosol (SIA) species of sulfate, nitrate, and ammonium (49%), followed by organic matter (34%). The mass concentration and most of the chemical components of PM_2.5 showed clear seasonal variation, with a winter-high and summer-low pattern. The winter-to-summer sulfate ratio and the winter organic carbon (OC)-to-elemental carbon (EC) ratio were unusually high compared with those in previous studies. Strong correlations of both the sulfate level and the sulfur oxidation ratio with relative humidity, and between water-soluble OC (WSOC) and SIA in winter, suggest the importance of aqueous phase chemistry for secondary aerosols. A strong correlation between non-sea salt sulfate and Na⁺ levels, a high Cl^-/Na⁺ ratio, and an unusual positive correlation between the nitrogen oxidation ratio and temperature during the winter indicate the influence of transported secondary emission sources from upwind urban areas and from China across the Yellow Sea. Despite the absence of local forest fires and the regulation of wood burning, a high levoglucosan concentration and its correlations with OC and WSOC indicate that Seoul was affected by biomass burning sources in the winter. The unusually high water-insoluble OC (WIOC)-to-EC ratio in winter implies additional transported combustion sources of WIOC. The strong correlation between WIOC and levoglucosan suggests the likely influence of transported biomass burning sources on the high WIOC/EC ratio during the winter.

Realtime chemical characterization of post monsoon organic aerosols in a polluted urban city: Sources, composition, and comparison with other seasons

Real time chemical characterization of non-refractory submicron aerosols (NR-PM₁) was carried out during post monsoon (September-October) via Aerosol Mass Spectrometer (AMS) at a polluted urban location of Kanpur, India. Organic aerosol (OA) was found to be the dominant species with 58% contribution to total NR-PM₁ mass, followed by sulfate (16%). Overall, OA was highly oxidized (average O/C = 0.66) with the dominance of oxidized OAs (60% of total OA) as revealed by source apportionment. Oxidized nature of OA was also supported by very high OC/EC ratios (average = 8.2) obtained from simultaneous offline filter sampling. High and low OA loading periods have very dramatic effects on OA composition and oxidation. OA O/C ratios during lower OA loading periods were on average 30% higher than the same from high loading periods with significant changes in types and relative contribution from oxidized OAs (OOA). Comparison of OA sources and chemistry among post monsoon and other seasons revealed significant differences. Characteristics of primary OAs remain very similar, but features of OOAs showed substantial changes from one season to another. Winter had lowest OOA contribution to total OA but similar overall O/C ratios as other seasons. This reveals that processing of primary OAs, local atmospheric chemistry, and regional contributions can significantly alter OA characteristics from one season to another. This study provides interesting insights into the seasonal variations of OA sources and evolution in a very polluted and complex environment.

Overview of surface measurements and spatial characterization of submicrometer particulate matter during the DISCOVER-AQ 2013 campaign in Houston, TX

The sources of submicrometer particulate matter (PM₁) remain poorly characterized in the industrialized city of Houston, TX. A mobile sampling approach was used to characterize PM₁ composition and concentration across Houston based on high-time-resolution measurements of nonrefractory PM₁ and trace gases during the DISCOVER-AQ Texas 2013 campaign. Two pollution zones with marked differences in PM₁ levels, character, and dynamics were established based on cluster analysis of organic aerosol mass loadings sampled at 16 sites. The highest PM₁ mass concentrations (average 11.6 ± 5.7 µg/m³) were observed to the northwest of Houston (zone 1), dominated by secondary organic aerosol (SOA) mass likely driven by nighttime biogenic organonitrate formation. Zone 2, an industrial/urban area south/east of Houston, exhibited lower concentrations of PM₁ (average 4.4 ± 3.3 µg/m³), significant organic aerosol (OA) aging, and evidence of primary sulfate emissions. Diurnal patterns and backward-trajectory analyses enable the classification of airmass clusters characterized by distinct PM sources: biogenic SOA, photochemical aged SOA, and primary sulfate emissions from the Houston Ship Channel. Principal component analysis (PCA) indicates that secondary biogenic organonitrates primarily related with monoterpenes are predominant in zone 1 (accounting for 34% of the variability in the data set). The relevance of photochemical processes and industrial and traffic emission sources in zone 2 also is highlighted by PCA, which identifies three factors related with these processes/sources (~50% of the aerosol/trace gas concentration variability). PCA reveals a relatively minor contribution of isoprene to SOA formation in zone 1 and the absence of isoprene-derived aerosol in zone 2. The relevance of industrial amine emissions and the likely contribution of chloride-displaced sea salt aerosol to the observed variability in pollution levels in zone 2 also are captured by PCA.

IMPLICATIONS

This article describes an urban-scale mobile study to characterize spatial variations in submicrometer particulate matter (PM₁) in greater Houston. The data set indicates substantial spatial variations in PM₁ sources/chemistry and elucidates the importance of photochemistry and nighttime oxidant chemistry in producing secondary PM₁. These results emphasize the potential benefits of effective control strategies throughout the region, not only to reduce primary emissions of PM₁ from automobiles and industry but also to reduce the emissions of important secondary PM₁ precursors, including sulfur oxides, nitrogen oxides, ammonia, and volatile organic compounds. Such efforts also could aid in efforts to reduce mixing ratios of ozone.

Fine particles sampled at an urban background site and an industrialized coastal site in Northern France - Part 1: Seasonal variations and chemical characterization

The chemical composition of particulate matter sampled at two French Northern sites (Douai, DO - urban background; Grande-Synthe, GS - industrialized coastal site) was investigated during two summer and winter field campaigns at each site. Measurements of the major chemical species (organic, sulfate, nitrate, ammonium, chloride) in the non-refractory submicron aerosols (NR-PM₁) were carried out by a High Resolution Time-of-Flight Aerosol Mass Spectrometer. Black Carbon in PM_2.5 was monitored using an Aethalometer, while the OC and EC fractions and some targeted chemical organic families (polycyclic aromatic hydrocarbons, PAHs; dicarboxylic acids, DCAs) were quantified by the simultaneous collection of PM_2.5 on filters followed by offline analyses. The seasonal trends and winter-to-summer (W/S) concentration ratios are discussed in this paper. Results indicate that the total average mass concentrations of PM_2.5 varied between 20.5μgm^-3 and 32.6μgm^-3 in DO and between 10.6μgm^-3 and 29.9μgm^-3 in GS during summer and winter, respectively. Similar concentration patterns were found for PAHs and Organic Carbon (OC, representing ~80% of the total carbon) with highest concentrations in winter at the urban site. DCA concentrations showed less seasonal variations, although the highest value also appeared during winter. Total NR-PM₁ presented concentrations in summer lower by a factor of 4 (for DO) and 10 (for GS) than those observed in winter. Organics and nitrates dominated the NR-PM₁ in DO for both seasons and during winter in GS while sulfates and nitrates were the most dominant species in summer in GS. Average chloride concentrations were slightly more important in GS than those in DO related to its use in industrial processes and no significant seasonal trend was observed. The size-resolved chemical composition showed that aerosols sampled in DO in winter are more aged than those collected in GS where fresh emissions of sulfate from the industrial sector were observed.

Significant concentration changes of chemical components of PM1 in the Yangtze River Delta area of China and the implications for the formation mechanism of heavy haze-fog pollution

Since the winter season of 2013, a number of persistent haze-fog events have occurred in central-eastern China. Continuous measurements of the chemical and physical properties of PM1 at a regional background station in the Yangtze River Delta area of China from 16 Nov. to 18 Dec., 2013 revealed several haze-fog events, among which a heavy haze-fog event occurred between 6 Dec. and 8 Dec. The mean concentration of PM1 was 212μgm(-3) in the heavy haze-fog period, which was about 10 times higher than on clean days and featured a peak mass concentration that reached 298μgm(-3). Organics were the largest contributor to the dramatic rise of PM1 on heavy haze-fog days (average mass concentration of 86μgm(-3)), followed by nitrate (58μgm(-3)), sulfate (35μgm(-3)), ammonium (29μgm(-3)), and chloride (4.0μgm(-3)). Nitrate exhibited the largest increase (~20 factors), associated with a significant increase in NOx. This was mainly attributable to increased coal combustion emissions, relative to motor vehicle emissions, and was caused by short-distance pollutant transport within surrounding areas. Low-volatility oxidized organic aerosols (OA) (LV-OOA) and biomass-burning OA (BBOA) also increased sharply on heavy haze-fog days, exhibiting an enhanced oxidation capacity of the atmosphere and increased emissions from biomass burning. The strengthening of the oxidation capacity during the heavy pollution episode, along with lower solar radiation, was probably due to increased biomass burning, which were important precursors of O3. The prevailing meteorological conditions, including low wind and high relative humidity, and short distance transported gaseous and particulate matter surrounding of the sampling site, coincided with the increased pollutant concentrations mainly from biomass-burning mentioned above to cause the persistent haze-fog event in the YRD area.

Bibliometric analysis of research on secondary organic aerosols: A Science Citation Index Expanded-based analysis (IUPAC Technical Report)

This study was conceived to evaluate the global scientific output of secondary organic aerosol (SOA) research over the past 20 years and to assess the characteristics of the research patterns, tendencies, and methods in the papers. Data were based on the online version of Science Citation Index Expanded from 1992 to 2011. Publications referring to SOAs were assessed by distribution of the number of publications and times cited, source categories, source journals, author keywords, KeyWords Plus, and the most cited publications in these years. By synthetic analysis of author keywords, KeyWords Plus, titles, and abstracts, it was concluded that modeling is currently and will at least over the next decade continue to be the predominant research method to validate state-of-the-art knowledge of SOAs, and that the foci of SOA research will be the key precursors terpenes and isoprene, the mechanisms of oxidation and gas-phase reactions, and emission inventories.

Elucidating secondary organic aerosol from diesel and gasoline vehicles through detailed characterization of organic carbon emissions

Emissions from gasoline and diesel vehicles are predominant anthropogenic sources of reactive gas-phase organic carbon and key precursors to secondary organic aerosol (SOA) in urban areas. Their relative importance for aerosol formation is a controversial issue with implications for air quality control policy and public health. We characterize the chemical composition, mass distribution, and organic aerosol formation potential of emissions from gasoline and diesel vehicles, and find diesel exhaust is seven times more efficient at forming aerosol than gasoline exhaust. However, both sources are important for air quality; depending on a region's fuel use, diesel is responsible for 65% to 90% of vehicular-derived SOA, with substantial contributions from aromatic and aliphatic hydrocarbons. Including these insights on source characterization and SOA formation will improve regional pollution control policies, fuel regulations, and methodologies for future measurement, laboratory, and modeling studies.

Understanding atmospheric organic aerosols via factor analysis of aerosol mass spectrometry: a review

Organic species are an important but poorly characterized constituent of airborne particulate matter. A quantitative understanding of the organic fraction of particles (organic aerosol, OA) is necessary to reduce some of the largest uncertainties that confound the assessment of the radiative forcing of climate and air quality management policies. In recent years, aerosol mass spectrometry has been increasingly relied upon for highly time-resolved characterization of OA chemistry and for elucidation of aerosol sources and lifecycle processes. Aerodyne aerosol mass spectrometers (AMS) are particularly widely used, because of their ability to quantitatively characterize the size-resolved composition of submicron particles (PM₁). AMS report the bulk composition and temporal variations of OA in the form of ensemble mass spectra (MS) acquired over short time intervals. Because each MS represents the linear superposition of the spectra of individual components weighed by their concentrations, multivariate factor analysis of the MS matrix has proved effective at retrieving OA factors that offer a quantitative and simplified description of the thousands of individual organic species. The sum of the factors accounts for nearly 100% of the OA mass and each individual factor typically corresponds to a large group of OA constituents with similar chemical composition and temporal behavior that are characteristic of different sources and/or atmospheric processes. The application of this technique in aerosol mass spectrometry has grown rapidly in the last six years. Here we review multivariate factor analysis techniques applied to AMS and other aerosol mass spectrometers, and summarize key findings from field observations. Results that provide valuable information about aerosol sources and, in particular, secondary OA evolution on regional and global scales are highlighted. Advanced methods, for example a-priori constraints on factor mass spectra and the application of factor analysis to combined aerosol and gas phase data are discussed. Integrated analysis of worldwide OA factors is used to present a holistic regional and global description of OA. Finally, different ways in which OA factors can constrain global and regional models are discussed.

Apportionment of primary and secondary organic aerosols in southern California during the 2005 study of organic aerosols in riverside (SOAR-1)

Ambient sampling was conducted in Riverside, California during the 2005 Study of Organic Aerosols in Riverside to characterize the composition and sources of organic aerosol using a variety of state-of-the-art instrumentation and source apportionmenttechniques. The secondary organic aerosol (SOA) mass is estimated by elemental carbon and carbon monoxide tracer methods, water soluble organic carbon content, chemical mass balance of organic molecular markers, and positive matrix factorization of high-resolution aerosol mass spectrometer data. Estimates obtained from each ofthese methods indicate that the organic fraction in ambient aerosol is overwhelmingly secondary in nature during a period of several weeks with moderate ozone concentrations and that SOA is the single largest component of PM1 aerosol in Riverside. Average SOA/OA contributions of 70-90% were observed during midday periods, whereas minimum SOA contributions of approximately 45% were observed during peak morning traffic periods. These results are contraryto previous estimates of SOAthroughout the Los Angeles Basin which reported that, other than during severe photochemical smog episodes, SOA was lower than primary OA. Possible reasons for these differences are discussed.

Source attribution of submicron organic aerosols during wintertime inversions by advanced factor analysis of aerosol mass spectra

Real-time measurements of submicrometer aerosol were performed using an Aerodyne aerosol mass spectrometer (AMS) during three weeks at an urban background site in Zurich (Switzerland) in January 2006. A hybrid receptor model which incorporates a priori known source composition was applied to the AMS highly time-resolved organic aerosol mass spectra. Three sources and components of submicrometer organic aerosols were identified: the major component was oxygenated organic aerosol (OOA), mostly representing secondary organic aerosol and accounting on average for 52-57% of the particulate organic mass. Radiocarbon (14C) measurements of organic carbon (OC) indicated that approximately 31 and approximately 69% of OOA originated from fossil and nonfossil sources, respectively. OOA estimates were strongly correlated with measured particulate ammonium. Particles from wood combustion (35-40%) and 3-13% traffic-related hydrocarbon-like organic aerosol (HOA) accounted for the other half of measured organic matter (OM). Emission ratios of modeled HOA to measured nitrogen oxides (NOx) and OM from wood burning to levoglucosan from filter analyses were found to be consistent with literature values.

Aging of organic aerosol: bridging the gap between laboratory and field studies

The oxidation of organics in aerosol particles affects the physical properties of aerosols through a process known as aging. Atmospheric particles compose a huge set of specific organic compounds, most of which have not been identified in field measurements. Laboratory experiments inevitably address model systems of reduced complexity to isolate critical chemical phenomena, but growing evidence suggests that composition effects may play a central role in the atmospheric aging of organic particles. In this review we seek to address the connections between recent laboratory studies and recent field campaigns addressing the aging of organic aerosols. We review laboratory studies on the uptake of oxidants, the evolution of particle-water interactions, and the evolution of particle density with aging. Finally, we review field data addressing condensed-phase lifetimes of organic tracers. These data suggest that although matrix effects identified in the laboratory have taken a step toward reconciling laboratory-field disagreements, further work is needed to understand the actual aging rates of organics in ambient particles.