Showing papers by "André S. H. Prévôt published in 2023"

Investigation of four-year chemical composition and organic aerosol sources of submicron particles at the ATOLL site in northern France.

Abstract: This study presents the first long-term online measurements of submicron (PM1) particles at the ATOLL (ATmospheric Observations in liLLe) platform, in northern France. The ongoing measurements using an Aerosol Chemical Speciation Monitor (ACSM) started at the end of 2016 and the analysis presented here spans through December 2020. At this site, the mean PM1 concentration is 10.6 μg m-3, dominated by organic aerosols (OA, 42.3%) and followed by nitrate (28.9%), ammonium (12.3%), sulfate (8.6%), and black carbon (BC, 8.0%). Large seasonal variations of PM1 concentrations are observed, with high concentrations during cold seasons, associated with pollution episodes (e.g. over 100 μg m-3 in January 2017). To study OA origins over this multiannual dataset we performed source apportionment analysis using rolling positive matrix factorization (PMF), yielding two primary OA factors, a traffic-related hydrocarbon-like OA (HOA) and biomass-burning OA (BBOA), and two oxygenated OA (OOA) factors. HOA showed a homogeneous contribution to OA throughout the seasons (11.8%), while BBOA varied from 8.1% (summer) to 18.5% (winter), the latter associated with residential wood combustion. The OOA factors were distinguished between their less and more oxidized fractions (LO-OOA and MO-OOA, on average contributing 32% and 42%, respectively). During winter, LO-OOA is identified as aged biomass burning, so at least half of OA is associated with wood combustion during this season. Furthermore, ammonium nitrate is also a predominant aerosol component during cold-weather pollution episodes - associated with fertilizer usage and traffic emissions. This study provides a comprehensive analysis of submicron aerosol sources at the recently established ATOLL site in northern France from multiannual observations, depicting a complex interaction between anthropogenic and natural sources, leading to different mechanisms of air quality degradation in the region across different seasons.

Impact of aging on the sources, volatility, and viscosity of organic aerosols in Chinese outflows

Abstract: Abstract. To investigate the impact of aging on the sources, volatility, and viscosity of organic aerosol (OA) in Chinese outflows, a high-resolution time-of-flight aerosol mass spectrometer (HR-AMS) coupled with a thermodenuder (TD) was deployed in the spring of 2018 in Dongying, which is a regional receptor site of metropolitan emissions in the North China Plain (NCP). The average mass concentration of PM1 is 31.5±22.7 µg m−3, which is mainly composed of nitrate (33 %) and OA (25 %). The source apportionment results show that the OA is mainly contributed by oxygenated OA (OOA) from secondary sources, including background-OOA (33 %) representing a background concentration of OA (2.6 µg m−3) in the NCP area, and transported-OOA (33 %) oxidized from urban emissions. The other two factors include aged hydrocarbon-liked OA (aged-HOA, 28 %) from transported vehicle emissions and biomass burning OA (BBOA, 5 %) from local open burning. The volatility of total OA (average C*=3.2×10-4 µg m−3) in this study is generally lower than that reported in previous field studies, which is mainly due to the high OA oxidation level resulting from aging processes during transport. The volatilities of OA factors follow the order of background-OOA (average C*=2.7×10-5 µg m−3) < transported-OOA (3.7×10-4µgm-3)< aged-HOA (8.1×10-4µgm-3)< BBOA (0.012 µg m−3). Extremely low volatilities in ambient air indicate that oligomers may exist in aged plumes. The viscosity estimation suggests that the majority of ambient OA in this study behaves as semisolid (60 %), liquifies at higher relative humidity (RH) (21 %), and solidifies (19 %) during noon when the RH is low and the oxidation level is high. Finally, the estimated mixing time of molecules in 200 nm OA varies dramatically from minutes at night to years in the afternoon, emphasizing the need to consider its dynamic kinetic limits when modeling OA. In general, the overall results of this study improve our understanding of the impact of aging on OA volatility and viscosity.

High-time-resolution chemical composition and source apportionment of PM 2.5 in northern 1 Chinese cities: implications for policy 2

Abstract: : Fine particulate matter (PM 2.5 ) pollution is still one of China's most important environmental issues, 15 especially in northern cities during wintertime. In this study, intensive real-time measurement campaigns were 16 conducted in Xi’an, Shijiazhuang, and Beijing to investigate the chemical characteristics and source contributions of 17 PM 2.5 and explore the formation progress of heavy pollution for policy implications. The chemical compositions of 18 PM 2.5 in three cities were all dominated by organic aerosol (OA) and nitrate (NO 3- ). Results of source apportionment 19 analyzed by hybrid environmental receptor model (HERM) showed that the secondary nitrate plus sulfate contributed 20 higher to PM 2.5 compared to other primary sources. Biomass burning was the dominant primary source in three pilot 21 cities. The contribution of coal combustion to PM 2.5 is non-negligible in Xi’an and Shijiazhuang but is no longer 22 important contributor in the capital city of Beijing due to the execution of a strict coal-banning policy. The potential 23 formation mechanisms of secondary aerosol in three cities were further explored by establishing the correlations 24 between the secondary nitrate plus sulfate and aerosol liquid water content (ALWC), and O x (O 3 + NO 2 ), respectively. 25 The results showed that photochemical oxidation and aqueous-phase reaction were two important pathways of 26 secondary aerosol formation. According to source variations, air pollution events that occurred in campaigns were 27 classified into three types: biomass combustion dominated, secondary nitrate plus sulfate dominated, and a 28 combination of primary and secondary sources. Additionally, this study compared the changes in chemical 29 composition and source contributions of PM 2.5 in past decades. The results suggested that the clean energy 30 replacements for rural household should be urgently encouraged to reduce the primary source emissions in northern 31

Bulk and molecular-level composition of primary organic 1 aerosol from wood, straw, cow dung, and plastic burning

Abstract: . During the past decades, the source apportionment of organic aerosol (OA) in the ambient air has been 11 improving substantially. The database of source retrieval model resolved mass spectral profiles for different 12 sources has been built with the aerosol mass spectrometer (AMS). However, distinguishing similar sources (such 13 as wildfires and residential wood burning) remains challenging, as the hard ionization of AMS mostly fragments 14 compounds and therefore cannot capture the detailed molecular information. Recent mass spectrometer 15 technologies of soft ionization and high mass resolution have allowed for aerosol characterization at the molecular 16 formula level. In this study, we systematically estimated the emission factors and characterized the primary OA 17 (POA) chemical composition with the AMS and the extractive electrospray ionization time-of-flight mass 18 spectrometer (EESI-TOF) for the first time from a variety of solid fuels, including beech logs, spruce and pine 19 logs, spruce and pine branches and needles, straw, cow dung, and plastic bags. The emission factors of organic 20 matter and hydrocarbon gases are 16.2 ± 10.8 g kg -1 and 30.3 ± 8.5 g kg -1 for cow dung burning, which is generally 21 higher than that of wood (beech, spruce, and pine), straw, and plastic bags burning (in the range from 1.3 to 6.2 g 22 kg -1 and 2.8 to 9.4 g kg -1 ). The POA measured by the AMS shows that the f 60 (mass fraction of m/z 60) varies from 23 0.003 to 0.04 based on fuel types and combustion efficiency for wood (beech, spruce, and pine) and cow dung 24 burning. The contribution of some polycyclic aromatic hydrocarbons is linked to burning fuels. On molecular 25 level, the dominant compound of POA from wood, straw, and cow dung is C 6 H 10 O 5 (mainly levoglucosan), 26 contributing ~7% to ~30% of the total intensity, followed by C 8 H 12 O 6 with fractions of ~2% to ~9%. However, 27 as they are prevalent in all burns of biomass material, they cannot act as tracers for the specific sources. By using 28 the Mann-Whitney U test among the studied fuels, we find specific potential new markers for these fuels from the 29 measurement of the AMS and EESI-TOF. Markers from spruce and pine burning could be resin and conifer 30 needle-related. The product from pyrolysis of hardwood lignins is found especially in beech logs burning. 31 Nitrogen-containing species are selected markers primarily for cow dung open burning. These markers provide 32 important support for the source apportionment. 33

Night-time NO emissions strongly suppress chlorine and nitrate radical formation during the winter in Delhi

Abstract: . Atmospheric pollution in urban regions is highly influenced by oxidants due to their important role in the formation of secondary organic aerosol (SOA) and smog. These include the nitrate radical (NO 3 ), which is typically considered a night-time oxidant, and the chlorine radical (Cl), an extremely potent oxidant that can be released in the morning in chloride-rich environments as a result of nocturnal build-up of nitryl chloride (ClNO 2 ). Chloride makes up a higher percentage of particulate 30 matter in Delhi than has been observed anywhere else in the world, which results in Cl having an unusually strong influence in this city. Here, we present observations and model results revealing that atmospheric chemistry in Delhi exhibits an unusual diel cycle, controlled by high concentrations of NO during the night. As a result of this, the formation of both NO 3 and dinitrogen pentoxide (N 2 O 5 ), a precursor of ClNO 2 and thus Cl, are suppressed at night and increase to unusually high levels during the day. Our results indicate that a substantial reduction in night-time NO has the potential to increase both nocturnal 35 oxidation via NO 3 and the production of Cl during the day.

Towards a better understanding of fine PM sources: Online and offline datasets combination in a single PMF.

Abstract: Source apportionment (SA) techniques allocate the measured ambient pollutants with their potential source origin; thus, they are a powerful tool for designing air pollution mitigation strategies. Positive Matrix Factorization (PMF) is one of the most widely used SA approaches, and its multi-time resolution (MTR) methodology, which enables mixing different instrument data in their original time resolution, was the focus of this study. One year of co-located measurements in Barcelona, Spain, of non-refractory submicronic particulate matter (NR-PM1), black carbon (BC) and metals were obtained by a Q-ACSM (Aerodyne Research Inc.), an aethalometer (Aerosol d.o.o.) and fine offline quartz-fibre filters, respectively. These data were combined in a MTR PMF analysis preserving the high time resolution (30 min for the NR-PM1 and BC, and 24 h every 4th day for the offline samples). The MTR-PMF outcomes were assessed varying the time resolution of the high-resolution data subset and exploring the error weightings of both subsets. The time resolution assessment revealed that averaging the high-resolution data was disadvantageous in terms of model residuals and environmental interpretability. The MTR-PMF resolved eight PM1 sources: ammonium sulphate + heavy oil combustion (25%), ammonium nitrate + ammonium chloride (17%), aged secondary organic aerosol (SOA) (16%), traffic (14%), biomass burning (9%), fresh SOA (8%), cooking-like organic aerosol (5%), and industry (4%). The MTR-PMF technique identified two more sources relative to the 24 h base case data subset using the same species and four more with respect to the pseudo-conventional approach mimicking offline PMF, indicating that the combination of both high and low TR data is significantly beneficial for SA. Besides the higher number of sources, the MTR-PMF technique has enabled some sources disentanglement compared to the pseudo-conventional and base case PMF as well as the characterisation of their intra-day patterns.

Real-time measurements of non-methane volatile organic compounds in the central Indo-Gangetic basin, Lucknow, India: source characterisation and their role in O3 and secondary organic aerosol formation

Abstract: Abstract. Lucknow is the capital of India's largest state, Uttar Pradesh, one of South Asia's most polluted urban cities. Tropospheric photochemistry relies on non-methane volatile organic compounds (NMVOCs), which are ozone and secondary organic aerosol precursors. Using the proton-transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) at an urban background site in Lucknow, the chemical characterisation of NMVOCs was performed in real time from December 2020 to May 2021. About ∼ 173 NMVOCs from m/z 31.018 to 197.216 were measured during the study period, including aromatics, non-aromatics, oxygenates, and nitrogen-containing compounds. The campaign daily mean concentrations of the NMVOCs were 125.5 ± 37.5 ppbv. The NMVOC daily average concentrations were about ∼ 30 % higher during the winter months (December–February) than in summer (March–May). The oxygenated volatile organic compounds and aromatics were the dominant VOC families, accounting for ∼ 57 %–80 % of the total NMVOC concentrations. Acetaldehyde, acetone, and acetic acid were the major NMVOC species, 5–15 times higher than the other species. An advanced multi-linear engine (ME-2) model was used to perform the NMVOC source apportionment using positive matrix factorisation (PMF). It resolves the five main sources contributing to these organic compounds in the atmosphere. They include traffic (23.5 %), two solid fuel combustion factors, SFC 1 (28.1 %) and SFC 2 (13.2 %), secondary volatile organic compounds (SVOCs) (18.6 %), and volatile chemical products (VCPs) (16.6 %). Aged and fresh emissions from solid fuel combustion (SFCs 1 and 2) were the dominant contributors to the total NMVOCs, and compounds related to these factors had a high secondary organic aerosol (SOA) formation potential. Interestingly, the traffic factor was the second-highest contributor to the total NMVOCs, and compounds related to this factor had a high ozone formation potential. Significant differences in the composition of the two solid fuel combustions indicate the influence of local emissions and transport of regional pollution to the city. The high temperature during summer leads to more volatilisation of oxygenated VOCs, related to the VCP factor. The study is the first attempt to highlight the sources of NMVOCs and their contribution to secondary pollutant (SOA and O3) formation in the city of Lucknow during winter and summer. The insights from the study would help various stakeholders to manage primary and secondary pollutants within the city.

Real-time measurements of NMVOCs in the central IGB, 1 Lucknow, India: Source characterization and their role in O 3 2 and SOA formation 3

Abstract: : 13 Lucknow is the capital of India’s largest state, Uttar Pradesh, one of South Asia’s most polluted urban cities. 14 Tropospheric photochemistry relies on non-methane volatile organic compounds (NMVOCs), which are ozone 15 and secondary organic aerosol precursors. Using the proton-transfer reaction time of flight mass spectrometer 16 (PTR-ToF-MS) at an urban background site in Lucknow, the chemical characterisation of NMVOCs was 17 performed in real-time from Dec-2020- May 2021. About ~173 NMVOCs from m/z 31.018 to 197.216 were 18 measured during the study period, including aromatics, non-aromatics, oxygenates, and nitrogen-containing 19 compounds. The campaign daily mean concentrations of the NMVOCs were 125.5 ±37.5 ppbv. The NMVOCs 20 daily average concentrations were about ~30% high during winter months (December-February) than in summer 21 (March-May). The oxygenated volatile organic compounds and aromatics were the dominant VOC families, 22 accounting for ~57-80% of the total NMVOCs concentrations. Acetaldehyde, acetone and acetic acid were the 23 major NMVOCs species, 5-15 times higher than other species. An advanced multi-linear engine (ME-2) model

A 1-year aerosol chemical speciation monitor (ACSM) source analysis of organic aerosol particle contributions from anthropogenic sources after long-range transport at the TROPOS research station Melpitz

Abstract: Abstract. Atmospheric aerosol particles are a complex combination of primary emitted sources (biogenic and anthropogenic) and secondary aerosol resulting from aging processes such as condensation, coagulation, and cloud processing. To better understand their sources, investigations have been focused on urban areas in the past, whereas rural-background stations are normally less impacted by surrounding anthropogenic sources. Therefore, they are predisposed for studying the impact of long-range transport of anthropogenic aerosols. Here, the chemical composition and organic aerosol (OA) sources of submicron aerosol particles measured by an aerosol chemical speciation monitor (ACSM) and a multi-angle absorption photometer (MAAP) were investigated at Melpitz from September 2016 to August 2017. The location of the station at the frontier between western and eastern Europe makes it the ideal place to investigate the impact of long-range transport over Europe. Indeed, the station is under the influence of less polluted air masses from westerly directions and more polluted continental air masses from eastern Europe. The OA dominated the submicron particle mass concentration and showed strong seasonal variability ranging from 39 % (in winter) to 58 % (in summer). It was followed by sulfate (15 % and 20 %) and nitrate (24 % and 11 %). The OA source identification was performed using the rolling positive matrix factorization (PMF) approach to account for the potential temporal changes in the source profile. It was possible to split OA into five factors with a distinct temporal variability and mass spectral signature. Three were associated with anthropogenic primary OA (POA) sources: hydrocarbon-like OA (HOA; 5.2 % of OA mass in winter and 6.8 % in summer), biomass burning OA (BBOA; 10.6 % and 6.1 %) and coal combustion OA (CCOA; 23 % and 8.7 %). Another two are secondary and processed oxygenated OA (OOA) sources: less oxidized OOA (LO-OOA; 28.4 % and 36.7 %) and more oxidized OOA (MO-OOA; 32.8 % and 41.8 %). Since equivalent black carbon (eBC) was clearly associated with the identified POA factors (sum of HOA, BBOA, and CCOA; R2= 0. 87), eBC's contribution to each of the POA factors was achieved using a multilinear regression model. Consequently, CCOA represented the main anthropogenic sources of carbonaceous aerosol (sum of OA and eBC) not only during winter (56 % of POA in winter) but also in summer (13 % of POA in summer), followed by BBOA (29 % and 69 % of POA in winter and summer, respectively) and HOA (15 % and 18 % of POA in winter and summer, respectively). A seasonal air mass cluster analysis was used to understand the geographical origins of the different aerosol types and showed that during both winter and summer time, PM1 (PM with an aerodynamic diameter smaller than 1 µm) air masses with eastern influence were always associated with the highest mass concentration and the highest coal combustion fraction. Since during wintertime CCOA is a combination of domestic heating and power plant emissions, the summer contribution of CCOA emphasizes the critical importance of coal power plant emissions to rural-background aerosols and its impact on air quality, through long-range transportation.