skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Sources and atmospheric dynamics of organic aerosol in New Delhi, India: insights from receptor modeling
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
Award ID(s):
1653625
PAR ID:
10129190
Author(s) / Creator(s):
; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Atmospheric Chemistry and Physics
Volume:
20
Issue:
2
ISSN:
1680-7324
Page Range / eLocation ID:
735 to 752
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; (, Atmospheric Chemistry and Physics)
    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. 
    more » « less
  2. ; ; ; ; (, Atmospheric Measurement Techniques)
    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. 
    more » « less
  3. ; ; ; ; ; ; ; ; ; ; et al (, Atmospheric Chemistry and Physics)
    Abstract. Subarctic cities notoriously experience severe winter pollution episodes with fine particle (PM2.5) concentrations above 35 µg m−3, the US Environmental Protection Agency (EPA) 24 h standard. While winter sources of primary particles in Fairbanks, Alaska, have been studied, the chemistry driving secondary particle formation is elusive. Biomass burning is a major source of wintertime primary particles, making the PM2.5 rich in light-absorbing brown carbon (BrC). When BrC absorbs sunlight, it produces photooxidants – reactive species potentially important for secondary sulfate and secondary organic aerosol formation – yet photooxidant measurements in high-latitude PM2.5 remain scarce. During the winter of 2022 Alaskan Layered Pollution And Chemical Analysis (ALPACA) field campaign in Fairbanks, we collected PM filters, extracted the filters into water, and exposed the extracts to simulated sunlight to characterize the production of three photooxidants: oxidizing triplet excited states of BrC, singlet molecular oxygen, and hydroxyl radical. Next, we used our measurements to model photooxidant production in highly concentrated aerosol liquid water. While conventional wisdom indicates photochemistry is limited during high-latitude winters, we find that BrC photochemistry is significant: we predict high triplet and singlet oxygen daytime particle concentrations up to 2×10-12 and 3×10-11 M, respectively, with moderate hydroxyl radical concentrations up to 5×10-15 M. Although our modeling predicts that triplets account for 0.4 %–10 % of daytime secondary sulfate formation, particle photochemistry cumulatively dominates, generating 76 % of daytime secondary sulfate formation, largely due to in-particle hydrogen peroxide, which contributes 25 %–54 %. Finally, we estimate triplet production rates year-round, revealing the highest rates in late winter when Fairbanks experiences severe pollution and in summer when wildfires generate BrC. 
    more » « less
  4. ; ; ; ; ; ; ; ; ; ; et al (, Atmospheric Chemistry and Physics)
    Abstract. This study describes a modeling framework, model evaluation, and source apportionment to understand the causes of Los Angeles (LA) air pollution. A few major updates are applied to the Community Multiscale Air Quality (CMAQ) model with a high spatial resolution (1 km × 1 km). The updates include dynamic traffic emissions based on real-time, on-road information and recent emission factors and secondary organic aerosol (SOA) schemes to represent volatile chemical products (VCPs). Meteorology is well predicted compared to ground-based observations, and the emission rates from multiple sources (i.e., on-road, volatile chemical products, area, point, biogenic, and sea spray) are quantified. Evaluation of the CMAQ model shows that ozone is well predicted despite inaccuracies in nitrogen oxide (NOx) predictions. Particle matter (PM) is underpredicted compared to concurrent measurements made with an aerosol mass spectrometer (AMS) in Pasadena. Inorganic aerosol is well predicted, while SOA is underpredicted. Modeled SOA consists of mostly organic nitrates and products from oxidation of alkane-like intermediate volatility organic compounds (IVOCs) and has missing components that behave like less-oxidized oxygenated organic aerosol (LO-OOA). Source apportionment demonstrates that the urban areas of the LA Basin and vicinity are NOx-saturated (VOC-sensitive), with the largest sensitivity of O3 to changes in VOCs in the urban core. Differing oxidative capacities in different regions impact the nonlinear chemistry leading to PM and SOA formation, which is quantified in this study. 
    more » « less
  5. ; ; ; (, Atmospheric Chemistry and Physics)
    Abstract. Understanding the properties and life cycle processes of aerosol particles inregional air masses is crucial for constraining the climate impacts ofaerosols on a global scale. In this study, characteristics of aerosols in theboundary layer (BL) and free troposphere (FT) of a remote continental regionin the western US were studied using a high-resolution time-of-flight aerosolmass spectrometer (HR-AMS) deployed at the Mount Bachelor Observatory (MBO;2763 m a.s.l.) in central Oregon in summer 2013. In the absence of wildfireinfluence, the average (±1σ) concentration of non-refractorysubmicrometer particulate matter (NR-PM1) at MBO was 2.8 (±2.8)µg m−3 and 84 % of the mass was organic. The otherNR-PM1 components were sulfate (11 %), ammonium (2.8 %),and nitrate (0.9 %). The organic aerosol (OA) at MBO from these cleanperiods showed clear diurnal variations driven by the boundary layer dynamicswith significantly higher concentrations occurring during daytime, upslopeconditions. NR-PM1 contained a higher mass fraction of sulfate andwas frequently acidic when MBO resided in the FT. In addition, OA in the FTwas found to be highly oxidized (average O∕C of 1.17) with lowvolatility while OA in BL-influenced air masses was moderately oxidized(average O∕C of 0.67) and semivolatile. There are indications thatthe BL-influenced OA observed at MBO was more enriched in organonitrates andorganosulfur compounds (e.g., MSA) and appeared to be representative ofbiogenic secondary organic aerosol (SOA) originated in the BL. A summary ofthe chemical compositions of NR-PM1 measured at a number of otherhigh-altitude locations in the world is presented and similar contrastsbetween FT and BL aerosols were observed. The significant compositional andphysical differences observed between FT and BL aerosols may have importantimplications for understanding the climate effects of regional backgroundaerosols. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email