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Advances in low-cost sensors (LCS) for monitoring air quality have opened new opportunities to characterize air quality in finer spatial and temporal resolutions. In this study, we deployed LCS that measure both gas (CO, NO, NO2, and O3) and particle concentrations and co-located research-grade instruments in Atlanta, GA, to investigate the capability of LCS in resolving air pollutant sources using non-negative matrix factorization (NMF) in a moderately polluted urban area. We provide a comparison of applying the NMF technique to both normalized and non-normalized data sets. We identify four factors with different temporal trends and properties for both normalized and non-normalized data sets. Both normalized and non-normalized LCS data sets can resolve primary organic aerosol (POA) factors identified from research-grade instruments. However, applying normalization provides factors with more diverse compositions and can resolve secondary organic aerosol (SOA). Results from this study demonstrate that LCS not only can be used to provide basic mass concentration information but also can be used for in-depth source apportionment studies even in an urban setting with complex pollution mixtures and relatively low aerosol loadings.
Assuntos
Poluentes Atmosféricos , Poluição do Ar , Aerossóis/análise , Poluentes Atmosféricos/análise , Poluição do Ar/análise , Monitoramento Ambiental/métodos , Material Particulado/análiseRESUMO
Organic aerosol (OA) generally accounts for a large fraction of fine particulate matter (PM2.5) in the urban atmosphere. Despite significant advances in the understanding their emission sources, transformation processes and optical properties in the submicron aerosol fraction (PM1), larger size fractions - e.g., PM2.5 - still deserve complementary investigations. In this study, we conducted a comprehensive analysis on sources, formation process and optical properties of OA in PM1 and PM2.5 under haze and foggy environments in the Yangtze River Delta (eastern China), using two aerosol chemical speciation monitors, as well as a photoacoustic extinctiometer at 870 nm. Positive matrix factorization analysis - using multilinear engine (ME2) algorithm - was conducted on PM1 and PM2.5 organic mass spectra. Four OA factors were identified, including three primary OA (POA) factors, i.e., hydrocarbon-like OA (HOA), cooking OA (COA), and biomass burning OA (BBOA), and a secondary OA (SOA) factor, i.e., oxidized oxygenated OA (OOA). An enhanced PM1-2.5 COA concentration was clearly observed during cooking peak hours, suggesting important contribution of fresh cooking emissions on large-sized particles (i.e., PM1-2.5). The oxidation state and concentration of PM2.5 HOA were higher than that in PM1, suggesting that large-sized HOA particles might be linked to oxidized POA. High contribution (44%) of large-sized OOA to non-refractory PM2.5 mass was observed during haze episodes. During foggy episodes, PM1 and PM2.5 OOA concentrations increased as a positive relationship over time, along with an exponential increase in the PM2.5-OOA to PM1-OOA ratio. Meanwhile, OOA loadings increased with the aerosol liquid water content (ALWC) during foggy episodes. Random forest cross-validation analysis also supported the important influence of ALWC on OOA variations, supporting substantial impact of aqueous process on SOA formation during haze and/or foggy episodes. Obtained results also indicated high OOA contributions (21%-36%) and low POA contributions (6%-14%) to the PM2.5 scattering coefficient during haze and foggy episodes, respectively. Finally, we could illustrate that atmospheric vertical diffusion and horizontal transport have important but different effects on the concentrations of different primary and secondary OA factors in different particle size fractions.
Assuntos
Poluentes Atmosféricos , Aerossóis/análise , Poluentes Atmosféricos/análise , China , Monitoramento Ambiental/métodos , Material Particulado/análise , RiosRESUMO
We measured the gas-particle partitioning of vehicle emitted primary organic aerosol (POA) in a traffic tunnel with three independent methods: artifact corrected bare-quartz filters, thermodenuder (TD) measurements, and thermal-desorption gas-chromatography mass-spectrometry (TD-GC-MS). Results from all methods consistently show that vehicle emitted POA measured in the traffic tunnel is semivolatile under a wide range of fleet compositions and ambient conditions. We compared the gas-particle partitioning of POA measured in both tunnel and dynamometer studies and found that volatility distributions measured in the traffic tunnel are similar to volatility distributions measured in the dynamometer studies, and predict similar gas-particle partitioning in the TD. These results suggest that the POA volatility distribution measured in the dynamometer studies can be applied to describe gas-particle partitioning of ambient POA emissions. The POA volatility distribution measured in the tunnel does not have significant diurnal or seasonal variations, which indicate that a single volatility distribution is adequate to describe the gas-particle partitioning of vehicle emitted POA in the urban environment.
Assuntos
Aerossóis , Emissões de Veículos , Poluentes Atmosféricos , Cromatografia Gasosa-Espectrometria de Massas , Tamanho da Partícula , VolatilizaçãoRESUMO
The high atmospheric concentrations of toxic gases, particulate matter, and acids in the areas immediately surrounding volcanoes can have negative impacts on human and ecological health. To better understand the atmospheric fate of volcanogenic emissions in the near field (in the first few hours after emission), we have carried out real-time measurements of key chemical components of the volcanic plume from KiÌ lauea on the Island of Hawai'i. Measurements were made at two locations, one â¼ 3 km north-northeast of the vent and the other 31 km to the southwest, with sampling at each site spanning a range of meteorological conditions and volcanic influence. Instrumentation included a sulfur dioxide monitor and an Aerosol Chemical Speciation Monitor, allowing for a measurement of the partitioning between the two major sulfur species (gas-phase SO2 and particulate sulfate) every 5 min. During trade wind conditions, which sent the plume toward the southwest site, sulfur partitioning exhibited a clear diurnal pattern, indicating photochemical oxidation of SO2 to sulfate; this enabled the quantitative determination of plume age (5 h) and instantaneous SO2 oxidation rate (2.4 × 10(-6) s(-1) at solar noon). Under stagnant conditions near the crater, the extent of SO2 oxidation was substantially higher, suggesting faster oxidation. The particles within the plume were extremely acidic, with pH values (controlled largely by ambient relative humidity) as low as -0.8 and strong acidity (controlled largely by absolute sulfate levels) up to 2200 nmol/m(3). The high variability of sulfur partitioning and particle composition underscores the chemically dynamic nature of volcanic plumes, which may have important implications for human and ecological health.
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Dióxido de Enxofre/análise , Enxofre/análise , Erupções Vulcânicas/análise , Aerossóis/análise , Gases , Havaí , Humanos , Concentração de Íons de Hidrogênio , Espectrometria de Massas , Oxirredução , Material Particulado/análise , Sulfatos/análise , Enxofre/química , Dióxido de Enxofre/química , VentoRESUMO
Secondary organic aerosol (SOA) formation from in-use vehicle emissions was investigated using a potential aerosol mass (PAM) flow reactor deployed in a highway tunnel in Pittsburgh, Pennsylvania. Experiments consisted of passing exhaust-dominated tunnel air through a PAM reactor over integrated hydroxyl radical (OH) exposures ranging from â¼ 0.3 to 9.3 days of equivalent atmospheric oxidation. Experiments were performed during heavy traffic periods when the fleet was at least 80% light-duty gasoline vehicles on a fuel-consumption basis. The peak SOA production occurred after 2-3 days of equivalent atmospheric oxidation. Additional OH exposure decreased the SOA production presumably due to a shift from functionalization to fragmentation dominated reaction mechanisms. Photo-oxidation also produced substantial ammonium nitrate, often exceeding the mass of SOA. Analysis with an SOA model highlight that unspeciated organics (i.e., unresolved complex mixture) are a very important class of precursors and that multigenerational processing of both gases and particles is important at longer time scales. The chemical evolution of the organic aerosol inside the PAM reactor appears to be similar to that observed in the atmosphere. The mass spectrum of the unoxidized primary organic aerosol closely resembles ambient hydrocarbon-like organic aerosol (HOA). After aging the exhaust equivalent to a few hours of atmospheric oxidation, the organic aerosol most closely resembles semivolatile oxygenated organic aerosol (SV-OOA) and then low-volatility organic aerosol (LV-OOA) at higher OH exposures. Scaling the data suggests that mobile sources contribute â¼ 2.9 ± 1.6 Tg SOA yr(-1) in the United States, which is a factor of 6 greater than all mobile source particulate matter emissions reported by the National Emissions Inventory. This highlights the important contribution of SOA formation from vehicle exhaust to ambient particulate matter concentrations in urban areas.
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Aerossóis/análise , Aerossóis/química , Poluentes Atmosféricos/análise , Emissões de Veículos/análise , Atmosfera/análise , Cidades , Gasolina/análise , Radical Hidroxila/análise , Nitratos/análise , Compostos Orgânicos/análise , Oxirredução , Material Particulado/análise , Pennsylvania , Estados Unidos , Compostos Orgânicos Voláteis/químicaRESUMO
Photoionization efficiency spectra of (14)N2, (15)N(14)N, and (15)N2 from 15.5 to 18.9 eV were measured using synchrotron radiation at the Advanced Light Source at Lawrence Berkeley National Laboratory with a resolution of 6 meV, and significant changes in peak energies and intensities upon isotopic substitution were observed. Previously, we reported the isotope shifts and their applications to Titan's atmosphere. Here, we report more extensive experimental details and tabulate the isotope shifts of many transitions in the N2 spectrum, including those for (15)N(14)N, which have not been previously reported. The isotope shifts are used to address several long-standing ambiguities in spectral peak assignments just above the ionization threshold of N2. The feature at 15.677 eV (the so-called second "cathedral" peak) is of particular interest in this respect. The measured isotope shifts for this peak relative to (14)N2 are 0.015 ± 0.001 eV for (15)N2 and 0.008 ± 0.001 eV for (15)N(14)N, which match most closely with the isotope shifts predicted for transitions to the (A (2)Πu v' = 2)4sσ(g) (1)Π(u) state using Herzberg equations for the isotopic differences in harmonic oscillator energy levels plus the first anharmonic correction of 0.0143 eV for (15)N2 and 0.0071 eV for (15)N(14)N. More generally, the isotope shifts measured for both (15)N2 and (15)N(14)N relative to (14)N2 provide new benchmarks for theoretical calculations of interferences between direct and indirect autoionization states which can interact to produce intricate resonant structures in molecular photoionization spectra in regions near ionization thresholds.
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Real-time continuous chemical measurements of fine aerosol were made using an Aerodyne Aerosol Chemical Speciation Monitor (ACSM) during summer and fall 2011 in downtown Atlanta, Georgia. Organic mass spectra measured by the ACSM were analyzed by positive matrix factorization (PMF), yielding three conventional factors: hydrocarbon-like organic aerosol (HOA), semivolatile oxygenated organic aerosol (SV-OOA), and low-volatility oxygenated organic aerosol (LV-OOA). An additional OOA factor that contributed to 33 ± 10% of the organic mass was resolved in summer. This factor had a mass spectrum that strongly correlated (r(2) = 0.74) to that obtained from laboratory-generated secondary organic aerosol (SOA) derived from synthetic isoprene epoxydiols (IEPOX). Time series of this additional factor is also well correlated (r(2) = 0.59) with IEPOX-derived SOA tracers from filters collected in Atlanta but less correlated (r(2) < 0.3) with a methacrylic acid epoxide (MAE)-derived SOA tracer, α-pinene SOA tracers, and a biomass burning tracer (i.e., levoglucosan), and primary emissions. Our analyses suggest IEPOX as the source of this additional factor, which has some correlation with aerosol acidity (r(2) = 0.3), measured as H(+) (nmol m(-3)), and sulfate mass loading (r(2) = 0.48), consistent with prior work showing that these two parameters promote heterogeneous chemistry of IEPOX to form SOA.
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Aerossóis/análise , Poluentes Atmosféricos/análise , Butadienos/química , Monitoramento Ambiental/instrumentação , Monitoramento Ambiental/métodos , Compostos de Epóxi/química , Hemiterpenos/química , Pentanos/química , Poluentes Atmosféricos/química , Atmosfera , Monoterpenos Bicíclicos , Cidades , Georgia , Espectrometria de Massas/métodos , Espectrometria de Massas/normas , Monoterpenos/química , Padrões de Referência , Estações do AnoRESUMO
The San Joaquin Valley (SJV) of California has suffered persistent particulate matter (PM) pollution despite many years of control efforts. To further understand the chemical drivers of this problem and to support the development of State Implementation Plan for PM, a time-of-flight aerosol chemical speciation monitor (ToF-ACSM) outfitted with a PM2.5 lens and a capture vaporizer has been deployed at the Fresno-Garland air monitoring site of the California Air Resource Board (CARB) since Oct. 2018. The instrument measured non-refractory species in PM2.5 continuously at 10-min resolution. In this study, the data acquired from Oct. 2018 to May 2019 were analyzed to investigate the chemical characteristics, sources and atmospheric processes of PM2.5 in the SJV. Comparisons of the ToF-ACSM measurement with various co-located aerosol instruments show good agreements. The inter-comparisons indicated that PM2.5 in Fresno was dominated by submicron particles during the winter whereas refractory species accounted for a major fraction of PM2.5 mass during the autumn associated with elevated PM10 loadings. A rolling window positive matrix factorization analysis was applied to the organic aerosol (OA) mass spectra using the Multilinear Engine (ME-2) algorithm. Three distinct OA sources were identified, including vehicle emissions, local and regional biomass burning, and formation of oxygenated species. There were significant seasonal variations in PM2.5 composition and sources. During the winter, residential wood burning and oxidation of nitrogen oxides were major contributors to the occurrence of haze episodes with PM2.5 dominated by biomass burning OA and nitrate. In autumn, agricultural activities and wildfires were found to be the main cause of PM pollution. PM2.5 concentrations decreased significantly after spring and were dominated by oxygenated OA during March to May. Our results highlight the importance of using seasonally dependent control strategies to mitigate PM pollution in the SJV.