Characterization of primary and aged wood burning and coal combustion organic aerosols in an environmental chamber and its implications for atmospheric aerosols

Particulate matter (PM) affects visibility, climate, and public health. Organic matter (OM), a uniquely complex portion of PM, can make up more than half of total atmospheric fine PM mass. We investigated the effect of aging on secondary organic aerosol (SOA) concentration and composition for wood burning (WB) and coal combustion (CC) emissions, two major atmospheric OM sources, using mid-infrared (MIR) spectroscopy and aerosol mass spectrometry (AMS). For this purpose, primary emissions were injected into an environmental chamber and aged using hydroxyl (diurnal aging) and nitrate (nocturnal aging) radicals to reach an atmospherically relevant oxidative age. A time-of-flight AMS instrument was used to measure the high-time-resolution composition of non-refractory fine PM, while fine PM was collected on PTFE filters before and after aging for MIR analysis. AMS and MIR spectroscopy indicate an approximately 3-fold enhancement of organic aerosol (OA) concentration after aging (not wall-loss corrected). The OM:OC ratios also agree closely between the two methods and increase, on average, from 1.6 before aging to 2 during the course of aging. MIR spectroscopy, which is able to differentiate among oxygenated groups, shows a distinct functional group composition for aged WB (high abundance of carboxylic acids) and CC OA (high abundance of non-acid carbonyls) and detects aromatics and polycyclic aromatic hydrocarbons (PAHs) in emissions of both sources. The MIR spectra of fresh WB and CC aerosols are reminiscent of their parent compounds with differences in specific oxygenated functional groups after aging, consistent with expected oxidation pathways for volatile organic compounds (VOCs) of each emission source. The AMS mass spectra also show variations due to source and aging that are consistent with the MIR functional group (FG) analysis. Finally, a comparison of the MIR spectra of aged chamber WB OA with that of ambient samples affected by residential wood burning and wildfires reveals similarities regarding the high abundance of organics, especially acids, and the visible signatures of lignin and levoglucosan. This finding is beneficial for the source identification of atmospheric aerosols and interpretation of their complex MIR spectra.

Chemical characterization of organic aerosols with a focus on biomass burning and mid-infrared spectroscopy

Amir Yazdani

Aerosols play a significant role in the atmosphere through affecting the radiative budget, cloud condensation nuclei activity, and visibility. They also cause adverse health effects leading to premature deaths. A major fraction of aerosols is organic matter (OM), which has a complex composition, is produced by various sources, and undergoes chemical transformation in the atmosphere, making its full characterization difficult. Biomass burning has become a major source of OM with an increasing effect due to more frequent large wildfires around the world resulting partly from climate change.In this thesis, Fourier transform infrared spectroscopy (FTIR) has been employed in six different projects as the main tool to characterize OM from various sources especially biomass burning in order to understand its formation and evolution in the atmosphere. This technique has been used to analyze the functional group (FG) composition of OM, specific spectral profiles from different sources, and biomass burning marker signatures in a nondestructive and cost-efficient manner. FTIR has also been combined with other analytical techniques. First, we used the spectral profiles in the aliphatic CH region of IR spectra to extract information about the molecular structure of atmospheric organic aerosols in terms of their mean carbon number and molecular weight. We found that urban, rural, and biomass burning aerosols have distinct mean molecular weights and carbon numbers. FTIR and aerosol mass spectrometry (AMS) were used in the second project to characterize burning aerosols in an environmental simulation chamber. We showed the agreement of these two instruments in terms of the OM mass concentration and elemental ratios (H:C, and O:C). We found that AMS spectra contained functional group information that agreed with that of FTIR even for moderately aged aerosols. In the third project, we used univariate and multivariate statistics to combine FTIR and AMS measurements to better understand and interpret the complex AMS mass spectra in terms of the FG composition and to estimate the high-time-resolution FG composition of combustion aerosols during the course of aging. In another environmental chamber study (the fourth project), we developed a procedure to estimate the often-neglected evolution of primary biomass burning aerosols during daytime and nighttime chemical agings. We found that at least 15 % of the primary aerosol mass undergoes chemical transformation at relatively short time scales in the order of a day in the atmosphere. Organic biomass burning markers were among the fastest decaying species, making the identification of aged biomass burning aerosols in the atmosphere challenging. In the fifth project, we used the biomass burning marker signatures in the FTIR spectra for the first time to identify and quantify atmospheric samples affected by wood smoke. The FTIR-based identification method agreed well with those using ion chromatography and satellite observations. This method, which is one of the few scalable to large air pollution monitoring networks, was applied to around 20,000 filters collected across the US in 2015 to estimate the impact of biomass burning. In the sixth project, we used FTIR to characterize OM emitted from different cookstoves and fuels. We found similarities between the spectra of unburned fuels and OM emissions and measured high abundances of aromatics and polycyclic aromatic hydrocarbons in the particulate emissions.

EPFL2022

Fragment ion-functional group relationships in organic aerosols using aerosol mass spectrometry and mid-infrared spectroscopy

Nikunj Dudani, Satoshi Takahama, Amir Yazdani

Aerosol mass spectrometry (AMS) and mid-infrared spectroscopy (MIR) are two analytical methods for characterizing the chemical composition of OM. While AMS provides high-temporal-resolution bulk measurements, the extensive fragmentation during the electron impact (EI) ionization makes the characterization of OM components limited. The analysis of aerosols collected on PTFE filters using MIR, on the other hand, provides functional group (FG) information with reduced sample alteration but results in a relatively low temporal resolution. In this work, we compared and combined MIR and AMS measurements for several environmental chamber experiments to achieve a better understanding of the AMS spectra and the OM chemical evolution by aging. Fresh emissions of wood and coal burning were injected into an environmental simulation chamber and aged with hydroxyl and nitrate radicals. A high-resolution time-of-flight (HR-TOF) AMS measured the bulk chemical composition of fine PM. Fine aerosols were also sampled on PTFE filters before and after aging for the offline MIR analysis. After comparing AMS and MIR bulk measurements, we used multivariate statistics to identify the influential functional groups contributing to AMS OM mass for different aerosol sources and aging processes. We also identified the key mass fragments resulting from each functional group for the complex OM generated from biomass and fossil fuel combustion. Finally, we developed a statistical model that enables estimation of the high-time-resolution functional group composition of OM using collocated AMS and MIR measurements. Using this approach, AMS spectra can be used to interpolate the functional group measurements by MIR, allowing us to better understand the evolution of OM during the aging process.

European Geosciences Union2022

The role of Organophosphate Esters Flame Retardants and plasticizers (OPEs) in Phosphorus Cycle in the atmosphere of the Mediterranean Sea

Athanasios Nenes, Christos Panagiotopoulos, Kalliopi Violaki

The atmosphere is considered as an important external nutrient source for the marine environment, especially in remote ocean waters or the oligotrophic Mediterranean Sea. Phosphorus (P) is a critical nutrient affecting primary productivity in large areas of oceanic ecosystems. Much has been placed on inorganic P, while the importance of organic P as potential pool of bioavailable P is not widely recognized. In this study we quantify and speciate the anthropogenic organic P in the West and East Mediterranean atmosphere. Several anthropogenic organophosphorus compounds are analyzed, including pesticides (Phosmet, Malathion, Ethoprophos, Diazinon, Chloropyrifos-Me, Chloropyrifos-e), organophosphorus flame retardants and plasticizers (OPEs) (Tris- (1-chloro-2-propyl) phosphate (TCPP), tris[2-chloro-1-(chloromethyl)ethyl]phosphate (TDCP), Tris-(2-chloroethyl)phosphate (TCEP), tri-n-butyl phosphate (TnBP), triphenyl phosphate (TPhP), 2-ethylhexyl diphenyl phosphate (EHDPP)). Our analysis applied to Total Suspended atmospheric Particles (TSP) collected in Eastern (Crete, n = 67) and Western (Marseille, n = 25) Mediterranean Sea by using high-volume air sampler. The analysis performed with the liquid chromatography coupled to mass spectrometry (Q–TOF–LC/MS) after optimization of the analytical protocol for the aerosol samples. Five pesticides were found during the sampling period in East Mediterranean in total of 27 samples. The most frequent were chlorpyrifos–e (n = 9) and phosmet (n = 10) with average concentration 0.24±0.38 pmol m–3 and 0.24±0.45 pmol m–3, respectively following by diazinon (n = 4) at 0.07±0.00 pmol m–3. Higher concentration was estimated in chlorpyrifos-me at 0.91±0.93 pmol m–3 (n = 3) while ethoprophos was detected only in one sample (0.002 pmol m m–3), malathion was below detection limit. In the West Mediterranean, the most abundant organophosphate pesticides were phosmet (n = 3) with an average concentration of 0.07±0.04 pmol m–3, followed by diazinon (0.05 pmol m–3, n = 1) and chloropyrifos-e (0.04 pmol m–3, n = 2). Malathion, chlorpyrifos-me and ethoprophos were not detected. The average contribution of organophosphate pesticides in atmospheric organic P detected during this study was 0.2% and 0.1% for East and West Mediterranean, respectively. OPEs analyses in the same samples revealed higher concentrations in the West than in East Mediterranean atmosphere especially for TCPP, TCEP and TDCP, which are considered as the most potentially hazardous. In the West Med. the most abundant detected OPEs were the EHDPP (3.04±4.17 pmol m-3) and the TCPP (1.71±1.28 pmol m-3). In East Mediterranean, the most abundant detected OPEs were the TCPP (0.36±0.29 pmol m-3) and the TCEP (0.24±0.20 pmol m-3) whereas the TDCP and the EHDPP were not detected. The percentage contribution of OPEs in atmospheric organic–P over the West Mediterranean was 9%, while over East was 0.4%. The total anthropogenic organic P deposited in East Mediterranean during stratification period (June-September) was calculated at 8 tons, which was 4 times lower comparing with West Mediterranean (29 tons of P) during the same period. Overall, the above anthropogenic compounds represented only 0.4% of the total anthropogenic P deposited during stratification period, however their toxicity and fate to the marine environment warrants further investigations.