Light absorption spectra and carbon mass of fine particle water‐soluble components were measured during the summer of 2010 in the Los Angeles (LA) basin, California, and Atlanta, Georgia. Fresh LA ...secondary organic carbon had a consistent brown color and a bulk absorption per soluble carbon mass at 365 nm that was 4 to 6 times higher than freshly‐formed Atlanta soluble organic carbon. Radiocarbon measurements of filter samples show that LA secondary organic aerosol (SOA) was mainly from fossil carbon and chemical analysis of aqueous filter extracts identified nitro‐aromatics as one component of LA brown SOA. Interpreting soluble brown carbon as a property of freshly‐formed anthropogenic SOA, the difference in absorption per carbon mass between these two cities suggests most fresh secondary water‐soluble organic carbon formed within Atlanta is not from an anthropogenic process similar to LA. Contrasting emissions of biogenic volatile organic compounds may account for these differences.
Key Points
LA fresh SOA is 4–6 times more brown than Atlanta fresh SOA
Nitro‐aromatics are identified as a component of LA anthropogenic brown SOA
Atlanta SOA forms differently to LA due to biogenic/anthropogenic VOC mix
We spend about two thirds of our time in private homes where airborne particles of indoor and outdoor origins are present. The negative health effects of exposure to outdoor particles are known. The ...characteristics of indoor airborne particles, though, are not well understood. This study assesses the differences in chemical composition of PM1 (<1 μm) inside and outside of an occupied Swedish residence in real time with a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and an Aethalometer. The chemical composition and concentration of particles indoors showed large differences compared to outdoors. The average indoor concentration was 15 μg m
−3
and was higher than the outdoor 7 μg m
−3
. Organics dominated indoor particle composition (86% of the total mass) and originated from indoor sources (cooking, e-cigarette vaping). The average indoor to outdoor ratios were 5.5 for organic matter, 1.0 for black carbon, 0.6 for sulphate, 0.1 for nitrate, 0.2 for ammonium and 0.2 for chloride. The occupancy time accounted for 97% of the total measured period. Four factors were identified in the source apportionment of organic particle fraction by applying positive matrix factorization (PMF): two cooking factors, one e-cigarette factor and one outdoor contribution (OOA) organic factor penetrated from outside.
This study assesses aerosol chemical composition PM1 (<1 μm) with the state-of-the-art techniques inside and outside of an occupied residence.
Rapid industrialization and urbanization in developing countries has led to an increase in air pollution, along a similar trajectory to that previously experienced by the developed nations. In China, ...particulate pollution is a serious environmental problem that is influencing air quality, regional and global climates, and human health. In response to the extremely severe and persistent haze pollution experienced by about 800 million people during the first quarter of 2013 (refs 4, 5), the Chinese State Council announced its aim to reduce concentrations of PM2.5 (particulate matter with an aerodynamic diameter less than 2.5 micrometres) by up to 25 per cent relative to 2012 levels by 2017 (ref. 6). Such efforts however require elucidation of the factors governing the abundance and composition of PM2.5, which remain poorly constrained in China. Here we combine a comprehensive set of novel and state-of-the-art offline analytical approaches and statistical techniques to investigate the chemical nature and sources of particulate matter at urban locations in Beijing, Shanghai, Guangzhou and Xi'an during January 2013. We find that the severe haze pollution event was driven to a large extent by secondary aerosol formation, which contributed 30-77 per cent and 44-71 per cent (average for all four cities) of PM2.5 and of organic aerosol, respectively. On average, the contribution of secondary organic aerosol (SOA) and secondary inorganic aerosol (SIA) are found to be of similar importance (SOA/SIA ratios range from 0.6 to 1.4). Our results suggest that, in addition to mitigating primary particulate emissions, reducing the emissions of secondary aerosol precursors from, for example, fossil fuel combustion and biomass burning is likely to be important for controlling China's PM2.5 levels and for reducing the environmental, economic and health impacts resulting from particulate pollution.
During the past decades, the source apportionment of organic aerosol (OA) in ambient air has been improving substantially. The database of source retrieval model-resolved mass spectral profiles for ...different sources has been built with the aerosol mass spectrometer (AMS). However, distinguishing similar sources (such as wildfires and residential wood burning) remains challenging, as the hard ionization of the AMS mostly fragments compounds and therefore cannot capture detailed molecular information. Recent mass spectrometer technologies of soft ionization and high mass resolution have allowed for aerosol characterization at the molecular formula level. In this study, we systematically estimated the emission factors and characterized the primary OA (POA) chemical composition with the AMS and the extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF) for the first time from a variety of solid fuels, including beech logs, spruce and pine logs, spruce and pine branches and needles, straw, cow dung, and plastic bags. The emission factors of organic matter estimated by the AMS and hydrocarbon gases estimated by the total hydrocarbon analyzer are 16.2 ± 10.8 g kg−1 and 30.3 ± 8.5 g kg−1 for cow dung burning, which is generally higher than that of wood (beech, spruce, and pine), straw, and plastic bag burning (in the range from 1.1 to 6.2 g kg−1 and 14.1 to 19.3 g kg−1). The POA measured by the AMS shows that the f60 (mass fraction of m/z 60) varies from 0.003 to 0.04 based on fuel types and combustion efficiency for wood (beech, spruce, and pine) and cow dung burning. On a molecular level, the dominant compound of POA from wood, straw, and cow dung is C6H10O5 (mainly levoglucosan), contributing ∼ 7 % to ∼ 30 % of the total intensity, followed by C8H12O6 with fractions of ∼ 2 % to ∼ 9 %. However, as they are prevalent in all burning of biomass material, they cannot act as tracers for the specific sources. By using the Mann–Whitney U test among the studied fuels, we find specific potential new markers for these fuels from the measurement of the AMS and EESI-TOF. Markers from spruce and pine burning are likely related to resin acids (e.g., compounds with 20–21 carbon atoms). The product from the pyrolysis of hardwood lignins is found especially in beech log burning. Nitrogen-containing species are selected markers primarily for cow dung open burning. These markers in the future will provide support for the source apportionment.
Atmospheric pollution in urban regions is highly influenced by oxidants due to their important role in the formation of secondary organic aerosol (SOA) and smog. These include the nitrate radical ...(NO3), which is typically considered a nighttime oxidant, and the chlorine radical (Cl), an extremely potent oxidant that can be released in the morning in chloride-rich environments as a result of nocturnal build-up of nitryl chloride (ClNO2). Chloride makes up a higher percentage of particulate matter in Delhi than has been observed anywhere else in the world, which results in Cl having an unusually strong influence in this city. Here, we present observations and model results revealing that atmospheric chemistry in Delhi exhibits an unusual diel cycle that is controlled by high concentrations of NO during the night. As a result of this, the formation of both NO3 and dinitrogen pentoxide (N2O5), a precursor of ClNO2 and thus Cl, are suppressed at night and increase to unusually high levels during the day. Our results indicate that a substantial reduction in nighttime NO has the potential to increase both nocturnal oxidation via NO3 and the production of Cl during the day.
Source apportionment of organic aerosols (OAs) is of great importance to
better understand the health impact and climate effects of particulate matter
air pollution. Air quality models are used as ...potential tools to identify
OA components and sources at high spatial and temporal resolution; however,
they generally underestimate OA concentrations, and comparisons of their
outputs with an extended set of measurements are still rare due to the lack
of long-term experimental data. In this study, we addressed such challenges
at the European level. Using the regional Comprehensive Air Quality Model
with Extensions (CAMx) and a volatility basis set (VBS) scheme which was
optimized based on recent chamber experiments with wood burning and diesel
vehicle emissions, and which contains more source-specific sets compared to
previous studies, we calculated the contribution of OA components and defined
their sources over a whole-year period (2011). We modeled separately the
primary and secondary OA contributions from old and new diesel and gasoline
vehicles, biomass burning (mostly residential wood burning and agricultural
waste burning excluding wildfires), other anthropogenic sources (mainly
shipping, industry and energy production) and biogenic sources. An important
feature of this study is that we evaluated the model results with
measurements over a longer period than in previous studies, which
strengthens our confidence in our modeled source apportionment results.
Comparison against positive matrix factorization (PMF) analyses of aerosol
mass spectrometric measurements at nine European sites suggested that the
modified VBS scheme improved the model performance for total OA as well as
the OA components, including hydrocarbon-like (HOA), biomass burning (BBOA)
and oxygenated components (OOA). By using the modified VBS scheme, the mean
bias of OOA was reduced from −1.3 to −0.4 µg m−3
corresponding to a reduction of mean fractional bias from −45 % to
−20 %. The winter OOA simulation, which was largely underestimated in
previous studies, was improved by 29 % to 42 % among the evaluated
sites compared to the default parameterization. Wood burning was the dominant
OA source in winter (61 %), while biogenic emissions contributed
∼ 55 % to OA during summer in Europe on average. In both seasons,
other anthropogenic sources comprised the second largest component (9 %
in winter and 19 % in summer as domain average), while the average
contributions of diesel and gasoline vehicles were rather small
(∼ 5 %) except for the metropolitan areas where the highest
contribution reached 31 %. The results indicate the need to improve the
emission inventory to include currently missing and highly uncertain local
emissions, as well as further improvement of VBS parameterization for winter
biomass burning. Although this study focused on Europe, it can be applied in
any other part of the globe. This study highlights the ability of long-term
measurements and source apportionment modeling to validate and improve
emission inventories, and identify sources not yet properly included in
existing inventories.
The Po Valley (Italy) is a well-known air quality hotspot characterized by
particulate matter (PM) levels well above the limit set by the European Air
Quality Directive and by the World Health ...Organization, especially during
the colder season. In the framework of Emilia-Romagna regional project
“Supersito”, the southern Po Valley submicron aerosol chemical composition
was characterized by means of high-resolution aerosol mass spectroscopy
(HR-AMS) with the specific aim of organic aerosol (OA) characterization and
source apportionment. Eight intensive observation periods (IOPs) were
carried out over 4 years (from 2011 to 2014) at two different sites
(Bologna, BO, urban background, and San Pietro Capofiume, SPC, rural
background), to characterize the spatial variability and seasonality of the
OA sources, with a special focus on the cold season. On the multi-year basis of the study, the AMS observations show that OA
accounts for averages of 45±8 % (ranging from 33 % to 58 %) and 46±7 % (ranging from 36 % to 50 %) of the total non-refractory submicron particle
mass (PM1-NR) at the urban and rural sites, respectively. Primary
organic aerosol (POA) comprises biomass burning (23±13 % of OA) and fossil fuel (12±7 %) contributions with a marked seasonality in concentration. As expected, the biomass burning contribution to POA is more
significant at the rural site (urban / rural concentration ratio of 0.67),
but it is also an important source of POA at the urban site during the cold
season, with contributions ranging from 14 % to 38 % of the total OA mass. Secondary organic aerosol (SOA) contributes to OA mass to a much larger
extent than POA at both sites throughout the year (69±16 % and
83±16 % at the urban and rural sites, respectively), with important
implications for public health. Within the secondary fraction of OA, the
measurements highlight the importance of biomass burning aging products
during the cold season, even at the urban background site. This biomass
burning SOA fraction represents 14 %–44 % of the total OA mass in the cold
season, indicating that in this region a major contribution of combustion
sources to PM mass is mediated by environmental conditions and atmospheric
reactivity. Among the environmental factors controlling the formation of SOA in the Po
Valley, the availability of liquid water in the aerosol was shown to play a
key role in the cold season. We estimate that the organic fraction originating
from aqueous reactions of biomass burning products (“bb-aqSOA”) represents
21 % (14 %–28 %) and 25 % (14 %–35 %) of the total OA mass and 44 %
(32 %–56 %) and 61 % (21 %–100 %) of the SOA mass at the urban and rural
sites, respectively.
Aromatic hydrocarbons (ArHCs) and oxygenated aromatic hydrocarbons (ArHC–OHs) are emitted from a variety of anthropogenic activities and are important precursors of secondary organic aerosol (SOA) in ...urban areas. Here, we analyzed and compared the composition of SOA formed from the oxidation of a mixture of aromatic VOCs by OH and NO3 radicals. The VOC mixture was composed of toluene (C7H8), p-xylene + ethylbenzene (C8H10), 1,3,5-trimethylbenzene (C9H12), phenol (C6H6O), cresol (C7H8O), 2,6-dimethylphenol (C8H10O), and 2,4,6-trimethylphenol (C9H12O) in a proportion where the aromatic VOCs were chosen to approximate day-time traffic-related emissions in Delhi, and the aromatic alcohols make up 20% of the mixture. These VOCs are prominent in other cities as well, including those influenced by biomass combustion. In the NO3 experiments, large contributions from C x H y O z N dimers (C15–C18) were observed, corresponding to fast SOA formation within 15–20 min after the start of chemistry. Additionally, the dimers were a mixture of different combinations of the initial VOCs, highlighting the importance of exploring SOAs from mixed VOC systems. In contrast, the experiments with OH radicals yielded gradual SOA mass formation, with C x H y O z monomers (C6–C9) being the dominant constituents. The evolution of SOA composition with time was tracked and a fast degradation of dimers was observed in the NO3 experiments, with concurrent formation of monomer species. The rates of dimer decomposition in NO3 SOA were ∼2–3 times higher compared to those previously determined for α-pinene + O3 SOA, highlighting the dependence of particle-phase reactions on VOC precursors and oxidants. In contrast, the SOA produced in the OH experiments did not dramatically change over the same time frame. No measurable effects of humidity were observed on the composition and evolution of SOA.
Ambient air pollution is one of the leading five health risks worldwide. One of the most harmful air pollutants is particulate matter (PM), which has different physical characteristics (particle size ...and number, surface area and morphology) and a highly complex and variable chemical composition. Our goal was first to comparatively assess the effects of exposure to PM regarding cytotoxicity, release of pro-inflammatory mediators and gene expression in human bronchial epithelia (HBE) reflecting normal and compromised health status. Second, we aimed at evaluating the impact of various PM components from anthropogenic and biogenic sources on the cellular responses. Air-liquid interface (ALI) cultures of fully differentiated HBE derived from normal and cystic fibrosis (CF) donor lungs were exposed at the apical cell surface to water-soluble PM filter extracts for 4 h. The particle dose deposited on cells was 0.9-2.5 and 8.8-25.4 μg per cm2 of cell culture area for low and high PM doses, respectively. Both normal and CF HBE show a clear dose-response relationship with increasing cytotoxicity at higher PM concentrations. The concurrently enhanced release of pro-inflammatory mediators at higher PM exposure levels links cytotoxicity to inflammatory processes. Further, the PM exposure deregulates genes involved in oxidative stress and inflammatory pathways leading to an imbalance of the antioxidant system. Moreover, we identify compromised defense against PM in CF epithelia promoting exacerbation and aggravation of disease. We also demonstrate that the adverse health outcome induced by PM exposure in normal and particularly in susceptible bronchial epithelia is magnified by anthropogenic PM components. Thus, including health-relevant PM components in regulatory guidelines will result in substantial human health benefits and improve protection of the vulnerable population.
To assign fossil and nonfossil contributions to carbonaceous particles, radiocarbon (14C) measurements were performed on organic carbon (OC), elemental carbon (EC), and water-insoluble OC (WINSOC) of ...aerosol samples from a regional background site in South China under different seasonal conditions. The average contributions of fossil sources to EC, OC and WINSOC were 38 ± 11%, 19 ± 10%, and 17 ± 10%, respectively, indicating generally a dominance of nonfossil emissions. A higher contribution from fossil sources to EC (∼51%) and OC (∼30%) was observed for air-masses transported from Southeast China in fall, associated with large fossil-fuel combustion and vehicle emissions in highly urbanized regions of China. In contrast, an increase of the nonfossil contribution by 5–10% was observed during the periods with enhanced open biomass-burning activities in Southeast Asia or Southeast China. A modified EC tracer method was used to estimate the secondary organic carbon from fossil emissions by determining 14C-derived fossil WINSOC and fossil EC. This approach indicates a dominating secondary component (70 ± 7%) of fossil OC. Furthermore, contributions of biogenic and biomass-burning emissions to contemporary OC were estimated to be 56 ± 16% and 44 ± 14%, respectively.
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