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Journal ArticleDOI

Real-time measurements of ambient aerosols in a polluted Indian city: Sources, characteristics, and processing of organic aerosols during foggy and nonfoggy periods

16 Sep 2015-Journal of Geophysical Research (John Wiley & Sons, Ltd)-Vol. 120, Iss: 17, pp 9006-9019
TL;DR: In this article, a detailed time-resolved chemical characterization of ambient nonrefractory submicron aerosols (NR-PM1) was conducted for the first time in India.
Abstract: A detailed time-resolved chemical characterization of ambient nonrefractory submicron aerosols (NR-PM1) was conducted for the first time in India. The measurements were performed during the winter (November 2011 to January 2012) in a heavily polluted city of Kanpur, which is situated in the Indo-Gangetic Plain. Real-time measurements provided new insights into the sources and evolution of organic aerosols (OA) that could not be obtained using previously deployed filter-based measurements at this site. The average NR-PM1 loading was very high (>100 µg/m3) throughout the study, with OA contributing approximately 70% of the total aerosol mass. Source apportionment of the OA using positive matrix factorization revealed large contributions from fresh and aged biomass burning OA throughout the entire study period. A back trajectory analysis showed that the polluted air masses were affected by local sources and distant source regions where the burning of paddy residues occurs annually during winter. Several fog episodes were encountered during the study, and the OA composition varied between foggy and nonfoggy periods, with higher oxygen to carbon (O/C) ratios during the foggy periods. The evolution of OA and their elemental ratios (O:C and H:C) were investigated for the possible effects of fog processing.

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Citations
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Journal ArticleDOI
TL;DR: It is shown that aqueous-phase processing has a dominant impact on the formation of more oxidized SOA (MO-OOA), and the contribution of MO-OO a to OA increases substantially as a function of relative humidity or liquid water content, while episodes analyses highlight that LO-OOB plays a more important role during the early stage of the formationof autumn/winter haze episodes while MO-ooA is more significant during the later evolution period.
Abstract: Secondary organic aerosol (SOA) constitutes a large fraction of OA, yet remains a source of significant uncertainties in climate models due to incomplete understanding of its formation mechanisms and evolutionary processes. Here we evaluated the effects of photochemical and aqueous-phase processing on SOA composition and oxidation degrees in three seasons in Beijing, China, using high-resolution aerosol mass spectrometer measurements along with positive matrix factorization. Our results show that aqueous-phase processing has a dominant impact on the formation of more oxidized SOA (MO–OOA), and the contribution of MO–OOA to OA increases substantially as a function of relative humidity or liquid water content. In contrast, photochemical processing plays a major role in the formation of less oxidized SOA (LO–OOA), as indicated by the strong correlations between LO–OOA and odd oxygen (Ox = O3 + NO2) during periods of photochemical production (R2 = 0.59–0.80). Higher oxygen-to-carbon ratios of SOA during perio...

181 citations

Journal ArticleDOI
TL;DR: In this paper, the authors report on 1.25 years of highly time-resolved speciated submicron particulate matter (PM 1 ) data, including black carbon (BC) and non-refractory PM 1 (NR-PM 1 ), which they combine to develop a composition-based estimate of PM 1.
Abstract: . Delhi, India, routinely experiences some of the world's highest urban particulate matter concentrations. We established the Delhi Aerosol Supersite study to provide long-term characterization of the ambient submicron aerosol composition in Delhi. Here we report on 1.25 years of highly time-resolved speciated submicron particulate matter (PM 1 ) data, including black carbon (BC) and nonrefractory PM 1 (NR-PM 1 ), which we combine to develop a composition-based estimate of PM 1 (“C-PM 1 ” = BC + NR-PM 1 ) concentrations. We observed marked seasonal and diurnal variability in the concentration and composition of PM 1 owing to the interactions of sources and atmospheric processes. Winter was the most polluted period of the year, with average C-PM 1 mass concentrations of ∼210 µ g m −3 . The monsoon was hot and rainy, consequently making it the least polluted (C-PM 1 ∼50 µ g m −3 ) period. Organics constituted more than half of the C-PM 1 for all seasons and times of day. While ammonium, chloride, and nitrate each were ∼10 % of the C-PM 1 for the cooler months, BC and sulfate contributed ∼5 % each. For the warmer periods, the fractional contribution of BC and sulfate to C-PM 1 increased, and the chloride contribution decreased to less than 2 %. The seasonal and diurnal variation in absolute mass loadings were generally consistent with changes in ventilation coefficients, with higher concentrations for periods with unfavorable meteorology – low planetary boundary layer height and low wind speeds. However, the variation in C-PM 1 composition was influenced by temporally varying sources, photochemistry, and gas–particle partitioning. During cool periods when wind was from the northwest, episodic hourly averaged chloride concentrations reached 50–100 µ g m −3 , ranking among the highest chloride concentrations reported anywhere in the world. We estimated the contribution of primary emissions and secondary processes to Delhi's submicron aerosol. Secondary species contributed almost 50 %–70 % of Delhi's C-PM 1 mass for the winter and spring months and up to 60 %–80 % for the warmer summer and monsoon months. For the cooler months that had the highest C-PM 1 concentrations, the nighttime sources were skewed towards primary sources, while the daytime C-PM 1 was dominated by secondary species. Overall, these findings point to the important effects of both primary emissions and more regional atmospheric chemistry on influencing the extreme particle concentrations that impact the Delhi megacity region. Future air quality strategies considering Delhi's situation in both a regional and local context will be more effective than policies targeting only local, primary air pollutants.

129 citations

Journal ArticleDOI
TL;DR: The surface particulate mAtter network (SPARTAN) is a long-term project that includes characterization of chemical and physical attributes of aerosols from filter samples collected worldwide.
Abstract: . The Surface PARTiculate mAtter Network (SPARTAN) is a long-term project that includes characterization of chemical and physical attributes of aerosols from filter samples collected worldwide. This paper discusses the ongoing efforts of SPARTAN to define and quantify major ions and trace metals found in fine particulate matter (PM2.5). Our methods infer the spatial and temporal variability of PM2.5 in a cost-effective manner. Gravimetrically weighed filters represent multi-day averages of PM2.5, with a collocated nephelometer sampling air continuously. SPARTAN instruments are paired with AErosol RObotic NETwork (AERONET) sun photometers to better understand the relationship between ground-level PM2.5 and columnar aerosol optical depth (AOD). We have examined the chemical composition of PM2.5 at 12 globally dispersed, densely populated urban locations and a site at Mammoth Cave (US) National Park used as a background comparison. So far, each SPARTAN location has been active between the years 2013 and 2016 over periods of 2–26 months, with an average period of 12 months per site. These sites have collectively gathered over 10 years of quality aerosol data. The major PM2.5 constituents across all sites (relative contribution ± SD) are ammoniated sulfate (20 % ± 11 %), crustal material (13.4 % ± 9.9 %), equivalent black carbon (11.9 % ± 8.4 %), ammonium nitrate (4.7 % ± 3.0 %), sea salt (2.3 % ± 1.6 %), trace element oxides (1.0 % ± 1.1 %), water (7.2 % ± 3.3 %) at 35 % RH, and residual matter (40 % ± 24 %). Analysis of filter samples reveals that several PM2.5 chemical components varied by more than an order of magnitude between sites. Ammoniated sulfate ranges from 1.1 µg m−3 (Buenos Aires, Argentina) to 17 µg m−3 (Kanpur, India in the dry season). Ammonium nitrate ranged from 0.2 µg m−3 (Mammoth Cave, in summer) to 6.8 µg m−3 (Kanpur, dry season). Equivalent black carbon ranged from 0.7 µg m−3 (Mammoth Cave) to over 8 µg m−3 (Dhaka, Bangladesh and Kanpur, India). Comparison of SPARTAN vs. coincident measurements from the Interagency Monitoring of Protected Visual Environments (IMPROVE) network at Mammoth Cave yielded a high degree of consistency for daily PM2.5 (r2 = 0.76, slope = 1.12), daily sulfate (r2 = 0.86, slope = 1.03), and mean fractions of all major PM2.5 components (within 6 %). Major ions generally agree well with previous studies at the same urban locations (e.g. sulfate fractions agree within 4 % for 8 out of 11 collocation comparisons). Enhanced anthropogenic dust fractions in large urban areas (e.g. Singapore, Kanpur, Hanoi, and Dhaka) are apparent from high Zn : Al ratios. The expected water contribution to aerosols is calculated via the hygroscopicity parameter κv for each filter. Mean aggregate values ranged from 0.15 (Ilorin) to 0.28 (Rehovot). The all-site parameter mean is 0.20 ± 0.04. Chemical composition and water retention in each filter measurement allows inference of hourly PM2.5 at 35 % relative humidity by merging with nephelometer measurements. These hourly PM2.5 estimates compare favourably with a beta attenuation monitor (MetOne) at the nearby US embassy in Beijing, with a coefficient of variation r2 = 0.67 (n = 3167), compared to r2 = 0.62 when κv was not considered. SPARTAN continues to provide an open-access database of PM2.5 compositional filter information and hourly mass collected from a global federation of instruments.

129 citations


Cites background or result from "Real-time measurements of ambient a..."

  • ...Chakraborty et al. (2015) measured 70 % organic mass composition and found a combined mass of 28 % for ASO4+ ANO3 compared to SPARTAN mass (26 %)....

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  • ...During the Kanpur collocation, relative fractions among the major species CM, sea salt, ASO4, and ANO3 all matched well with previous studies (Behera and Sharma, 2010; Chakraborty et al., 2015; Ram et al., 2012) that also sampled during winter dry seasons....

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Journal ArticleDOI

80 citations


Cites background from "Real-time measurements of ambient a..."

  • ...For example, Chakraborty et al. (2015) reported that the average NR‐PM1measured by AMS exceeded 100 μgm−3 in Kanpur in the Indo‐Gangetic Plain....

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Journal ArticleDOI
TL;DR: 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, and secondary OA was a ubiquitous and dominant aerosol component in all regions.
Abstract: 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 (602-813 μg m-3), whereas much lower values were observed in Korea, Japan, Singapore and regional background sites (75-151 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, eg, 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

74 citations

References
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Book
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TL;DR: In this paper, the authors present a model for the chemistry of the Troposphere of the atmosphere and describe the properties of the Atmospheric Aqueous phase of single aerosol particles.
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"Real-time measurements of ambient a..." refers background in this paper

  • ...The enhanced conversion of NH3 to NH4 + at low temperatures and high RH [Seinfeld and Pandis, 2006], and abundance of NH3 in this region [Behera and Sharma, 2010a; Ram et al., 2012; Behera et al., 2013] may have led to the neutralization of aerosols at this location....

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Journal ArticleDOI
TL;DR: In this paper, a new variant of Factor Analysis (PMF) is described, where the problem is solved in the weighted least squares sense: G and F are determined so that the Frobenius norm of E divided (element-by-element) by σ is minimized.
Abstract: A new variant ‘PMF’ of factor analysis is described. It is assumed that X is a matrix of observed data and σ is the known matrix of standard deviations of elements of X. Both X and σ are of dimensions n × m. The method solves the bilinear matrix problem X = GF + E where G is the unknown left hand factor matrix (scores) of dimensions n × p, F is the unknown right hand factor matrix (loadings) of dimensions p × m, and E is the matrix of residuals. The problem is solved in the weighted least squares sense: G and F are determined so that the Frobenius norm of E divided (element-by-element) by σ is minimized. Furthermore, the solution is constrained so that all the elements of G and F are required to be non-negative. It is shown that the solutions by PMF are usually different from any solutions produced by the customary factor analysis (FA, i.e. principal component analysis (PCA) followed by rotations). Usually PMF produces a better fit to the data than FA. Also, the result of PF is guaranteed to be non-negative, while the result of FA often cannot be rotated so that all negative entries would be eliminated. Different possible application areas of the new method are briefly discussed. In environmental data, the error estimates of data can be widely varying and non-negativity is often an essential feature of the underlying models. Thus it is concluded that PMF is better suited than FA or PCA in many environmental applications. Examples of successful applications of PMF are shown in companion papers.

4,797 citations


"Real-time measurements of ambient a..." refers methods in this paper

  • ...PMF analysis was carried out using the PMF evaluation tool [Paatero and Tapper, 1994; Ulbrich et al., 2009]....

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Journal ArticleDOI
TL;DR: In this article, an overview of the atmospheric degradation mechanisms for SOA precursors, gas-particle partitioning theory and analytical techniques used to determine the chemical composition of SOA is presented.
Abstract: Secondary organic aerosol (SOA) accounts for a significant fraction of ambient tropospheric aerosol and a detailed knowledge of the formation, properties and transformation of SOA is therefore required to evaluate its impact on atmospheric processes, climate and human health. The chemical and physical processes associated with SOA formation are complex and varied, and, despite considerable progress in recent years, a quantitative and predictive understanding of SOA formation does not exist and therefore represents a major research challenge in atmospheric science. This review begins with an update on the current state of knowledge on the global SOA budget and is followed by an overview of the atmospheric degradation mechanisms for SOA precursors, gas-particle partitioning theory and the analytical techniques used to determine the chemical composition of SOA. A survey of recent laboratory, field and modeling studies is also presented. The following topical and emerging issues are highlighted and discussed in detail: molecular characterization of biogenic SOA constituents, condensed phase reactions and oligomerization, the interaction of atmospheric organic components with sulfuric acid, the chemical and photochemical processing of organics in the atmospheric aqueous phase, aerosol formation from real plant emissions, interaction of atmospheric organic components with water, thermodynamics and mixtures in atmospheric models. Finally, the major challenges ahead in laboratory, field and modeling studies of SOA are discussed and recommendations for future research directions are proposed.

3,324 citations


"Real-time measurements of ambient a..." refers background in this paper

  • ...In recent years, advances in mass spectrometry and the development of the aerodyne aerosol mass spectrometer [DeCarlo et al., 2006; Canagaratna et al., 2007] have offered a unique opportunity for gaining insight into the evolution of OA in real time [Hallquist et al., 2009; Heald et al., 2010]....

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Journal ArticleDOI
11 Dec 2009-Science
TL;DR: A unifying model framework describing the atmospheric evolution of OA that is constrained by high–time-resolution measurements of its composition, volatility, and oxidation state is presented, which can serve as a basis for improving parameterizations in regional and global models.
Abstract: Organic aerosol (OA) particles affect climate forcing and human health, but their sources and evolution remain poorly characterized. We present a unifying model framework describing the atmospheric evolution of OA that is constrained by high-time-resolution measurements of its composition, volatility, and oxidation state. OA and OA precursor gases evolve by becoming increasingly oxidized, less volatile, and more hygroscopic, leading to the formation of oxygenated organic aerosol (OOA), with concentrations comparable to those of sulfate aerosol throughout the Northern Hemisphere. Our model framework captures the dynamic aging behavior observed in both the atmosphere and laboratory: It can serve as a basis for improving parameterizations in regional and global models.

3,104 citations

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