Abstract. Present methodologies for source apportionment assumefixed source profiles. Since meteorology and human activity patterns changeseasonally and diurnally, application of source apportionment techniques toshorter rather than longer time periods generates more representative massspectra. Here, we present a new method to conduct source apportionmentresolved by time of day using the underlying approach of positive matrixfactorization (PMF). We call this approach “time-of-day PMF” andstatistically demonstrate the improvements in this approach over traditionalPMF. We report on source apportionment conducted on four example timeperiods in two seasons (winter and monsoon seasons of 2017), using organic aerosolmeasurements from an aerosol chemical speciation monitor (ACSM). We deploythe EPA PMF tool with the underlying Multilinear Engine (ME-2) as the PMFsolver. Compared to the traditional seasonal PMF approach, we extract alarger number of factors as well as PMF factors that represent the expectedsources of primary organic aerosol using time-of-day PMF. By capturingdiurnal time series patterns of sources at a low computational cost,time-of-day PMF can utilize large datasets collected using long-termmonitoring and improve the characterization of sources of organic aerosolcompared to traditional PMF approaches that do not resolve by time of day.
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Contributions of primary sources to submicron organic aerosols in Delhi, India
Abstract. Delhi, India, experiences extremely high concentrations ofprimary organic aerosol (POA). Few prior source apportionment studies onDelhi have captured the influence of biomass burning organic aerosol (BBOA) and cooking organic aerosol(COA) on POA. In a companion paper, we develop a new method to conductsource apportionment resolved by time of day using the underlying approachof positive matrix factorization (PMF). We call this approach “time-of-dayPMF” and statistically demonstrate the improvements of this approach overtraditional PMF. Here, we quantify the contributions of BBOA, COA, andhydrocarbon-like organic aerosol (HOA) by applying positive matrixfactorization (PMF) resolved by time of day on two seasons (winter andmonsoon seasons of 2017) using organic aerosol measurements from an aerosol chemicalspeciation monitor (ACSM). We deploy the EPA PMF tool with the underlyingMultilinear Engine (ME-2) as the PMF solver. We also conduct detaileduncertainty analysis for statistical validation of our results. HOA is a major constituent of POA in both winter and the monsoon. In addition toHOA, COA is found to be a major constituent of POA in the monsoon, and BBOA isfound to be a major constituent of POA in the winter. Neither COA nor thedifferent types of BBOA were resolved in the seasonal (not time-resolved)analysis. The COA mass spectra (MS) profiles are consistent with massspectral profiles from Delhi and around the world, particularly resemblingMS of heated cooking oils with a high m/z 41. The BBOA MS have a very prominentm/z 29 in addition to the characteristic peak at m/z 60, consistent with previousMS observed in Delhi and from wood burning sources. In addition toseparating the POA, our technique also captures changes in MS profiles withthe time of day, a unique feature among source apportionment approachesavailable. In addition to the primary factors, we separate two to three oxygenated organicaerosol (OOA)components. When all factors are recombined to total POA and OOA, ourresults are consistent with seasonal PMF analysis conducted using EPA PMF.Results from this work can be used to better design policies that targetrelevant primary sources of organic aerosols in Delhi.
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- Award ID(s):
- 1653625
- NSF-PAR ID:
- 10376953
- Date Published:
- Journal Name:
- Atmospheric Chemistry and Physics
- Volume:
- 22
- Issue:
- 20
- ISSN:
- 1680-7324
- Page Range / eLocation ID:
- 13631 to 13657
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract To understand diurnal variations in PM2.5composition and aerosol extract absorption, PM2.5samples were collected at intervals of 2 hr from 8:00 to 20:00 and 6 hr from 20:00 to 8:00 (the next day) in northern Nanjing, China, during the winter and summer of 2019–2020 and analyzed for bulk components, organic tracers, and light absorption of water and methanol extracts—a proxy measure of brown carbon (BrC). Diurnal patterns of measured species reflected the influences of primary emissions and atmospheric processes. Light absorption coefficients of water (Abs365,
w ) and methanol extracts (Abs365,m ) at 365 nm shared a similar diurnal profile peaking at 18:00–20:00, generally following changes in biomass burning tracers. However, Abs365,w , Abs365,m , and their normalizations to organic aerosols increased at 14:00–16:00, earlier than that of levoglucosan in the late afternoon, which was attributed to secondarily formed BrC. The methanol extracts showed a less drastic decrease in light absorption at night than the water extracts and elevated absorption efficiency during 2:00–8:00. This is due to the fact that the water‐insoluble OC has a longer lifetime and stronger light absorption than the water‐soluble OC. According to the source apportionment results solved by positive matrix factorization (PMF), biomass burning and secondary formation were the major BrC sources in northern Nanjing, with an average total relative contribution of about 90%. Compared to previous studies, diurnal source cycles were added to the PMF simulations in this work by using time‐resolved speciation data, which avoided misclassification of BrC sources. -
Abstract. Delhi, India, is the second most populated city in the world and routinely experiences some of the highest particulate matter concentrations of any megacity on the planet, posing acute challenges to public health (World Health Organization, 2018). However, the current understanding of the sources and dynamics of PM pollution in Delhi is limited. Measurements at the Delhi Aerosol Supersite (DAS) provide long-term chemical characterization of ambient submicron aerosol in Delhi, with near-continuous online measurements of aerosol composition. Here we report on source apportionment based on positive matrix factorization (PMF), conducted on 15 months of highly time-resolved speciated submicron non-refractory PM1 (NR-PM1) between January 2017 and March 2018. We report on seasonal variability across four seasons of 2017 and interannual variability using data from the two winters and springs of 2017 and 2018. We show that a modified tracer-based organic component analysis provides an opportunity for a real-time source apportionment approach for organics in Delhi. Phase equilibrium modeling of aerosols using the extended aerosol inorganics model (E-AIM) predicts equilibrium gas-phase concentrations and allows evaluation of the importance of the ventilation coefficient (VC) and temperature in controlling primary and secondary organic aerosol. We also find that primary aerosol dominates severe air pollution episodes, and secondary aerosol dominates seasonal averages.more » « less
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null (Ed.)Abstract. The chemical complexity of biomass burning organic aerosol (BBOA) greatlyincreases with photochemical aging in the atmosphere, necessitatingcontrolled laboratory studies to inform field observations. In theseexperiments, BBOA from American white oak (Quercus alba) leaf andheartwood samples was generated in a custom-built emissions and combustionchamber and photochemically aged in a potential aerosol mass (PAM) flowreactor. A thermal desorption aerosol gas chromatograph (TAG) was used inparallel with a high-resolution time-of-flight aerosol mass spectrometer(AMS) to analyze BBOA chemical composition at different levels ofphotochemical aging. Individual compounds were identified and integrated toobtain relative decay rates for key molecules. A recently developedchromatogram binning positive matrix factorization (PMF) technique was usedto obtain mass spectral profiles for factors in TAG BBOA chromatograms,improving analysis efficiency and providing a more complete determination ofunresolved complex mixture (UCM) components. Additionally, the recentlycharacterized TAG decomposition window was used to track molecular fragmentscreated by the decomposition of thermally labile BBOA during sampledesorption. We demonstrate that although most primary (freshly emitted) BBOAcompounds deplete with photochemical aging, certain components eluting withinthe TAG thermal decomposition window are instead enhanced. Specifically, theincreasing trend in the decomposition m∕z 44 signal (CO2+)indicates formation of secondary organic aerosol (SOA) in the PAM reactor.Sources of m∕z 60 (C2H4O2+), typically attributed tofreshly emitted BBOA in AMS field measurements, were also investigated. Fromthe TAG chemical speciation and decomposition window data, we observed adecrease in m∕z 60 with photochemical aging due to the decay ofanhydrosugars (including levoglucosan) and other compounds, as well as anincrease in m∕z 60 due to the formation of thermally labile organic acidswithin the PAM reactor, which decompose during TAG sample desorption. Whenaging both types of BBOA (leaf and heartwood), the AMS data exhibit acombination of these two contributing effects, causing limited change to theoverall m∕z 60 signal. Our observations demonstrate the importance ofchemically speciated data in fully understanding bulk aerosol measurementsprovided by the AMS in both laboratory and field studies.more » « less
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Abstract. Urbanization and deforestation have important impacts on atmosphericparticulate matter (PM) over Amazonia. This study presents observations andanalysis of PM1 concentration, composition, and opticalproperties in central Amazonia during the dry season, focusing on theanthropogenic impacts. The primary study site was located 70 km downwind ofManaus, a city of over 2 million people in Brazil, as part of theGoAmazon2014/5 experiment. A high-resolution time-of-flight aerosol massspectrometer (AMS) provided data on PM1 composition, and aethalometermeasurements were used to derive the absorption coefficient babs,BrC ofbrown carbon (BrC) at 370 nm. Non-refractory PM1 mass concentrationsaveraged 12.2 µg m−3 at the primary study site, dominated byorganics (83 %), followed by sulfate (11 %). A decrease inbabs,BrC was observed as the mass concentration of nitrogen-containingorganic compounds decreased and the organic PM1 O:C ratio increased,suggesting atmospheric bleaching of the BrC components. The organic PM1was separated into six different classes by positive-matrix factorization(PMF), and the mass absorption efficiency Eabs associated with eachfactor was estimated through multivariate linear regression ofbabs,BrC on the factor loadings. The largest Eabs values wereassociated with urban (2.04±0.14 m2 g−1) and biomass-burning(0.82±0.04 to 1.50±0.07 m2 g−1) sources. Together, these sources contributed at least 80 % ofbabs,BrC while accounting for 30 % to 40 % of the organic PM1 massconcentration. In addition, a comparison of organic PM1 compositionbetween wet and dry seasons revealed that only part of the 9-foldincrease in mass concentration between the seasons can be attributed tobiomass burning. Biomass-burning factor loadings increased by 30-fold,elevating its relative contribution to organic PM1 from about 10 % inthe wet season to 30 % in the dry season. However, most of the PM1mass (>60 %) in both seasons was accounted for by biogenicsecondary organic sources, which in turn showed an 8-fold seasonalincrease in factor loadings. A combination of decreased wet deposition andincreased emissions and oxidant concentrations, as well as a positivefeedback on larger mass concentrations are thought to play a role in theobserved increases. Furthermore, fuzzy c-means clustering identified threeclusters, namely “baseline”, “event”, and “urban” to representdifferent pollution influences during the dry season. The baseline cluster,representing the dry season background, was associated with a mean massconcentration of 9±3 µg m−3. This concentration increasedon average by 3 µg m−3 for both the urban and the event clusters.The event cluster, representing an increased influence of biomass burningand long-range transport of African volcanic emissions, was characterized byremarkably high sulfate concentrations. The urban cluster, representing theinfluence of Manaus emissions on top of the baseline, was characterized byan organic PM1 composition that differed from the other two clusters.The differences discussed suggest a shift in oxidation pathways as well asan accelerated oxidation cycle due to urban emissions, in agreement withfindings for the wet season.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/acp-22-13631-2022
