Oxidized organic aerosol (OOA) is a major component of ambient particulate matter, substantially impacting climate, human health, and ecosystems. OOA is readily produced in the presence of sunlight, ...and requires days of photooxidation to reach the levels observed in the atmosphere. High concentrations of OOA are thus expected in the summer; however, our current mechanistic understanding fails to explain elevated OOA during wintertime periods of low photochemical activity that coincide with periods of intense biomass burning. As a result, atmospheric models underpredict OOA concentrations by a factor of 3 to 5. Here we show that fresh emissions from biomass burning exposed to NO₂ and O₃ (precursors to the NO₃ radical) rapidly form OOA in the laboratory over a few hours and without any sunlight. The extent of oxidation is sensitive to relative humidity. The resulting OOA chemical composition is consistent with the observed OOA in field studies in major urban areas. Additionally, this dark chemical processing leads to significant enhancements in secondary nitrate aerosol, of which 50 to 60% is estimated to be organic. Simulations that include this understanding of dark chemical processing show that over 70% of organic aerosol from biomass burning is substantially influenced by dark oxidation. This rapid and extensive dark oxidation elevates the importance of nocturnal chemistry and biomass burning as a global source of OOA.
The composition of fine particulate matter (PM) in two major Greek cities (Athens and Patras) was measured during two wintertime campaigns, one conducted in 2013 and the other in 2012. A major goal ...of this study is to quantify the sources of organic aerosol (OA) and especially residential wood burning, which has dramatically increased due to the Greek financial crisis. A high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed at both sites. PM with diameter less than 1 µm (PM1) consisted mainly of organics (60–75 %), black carbon (5–20 %), and inorganic salts (around 20 %) in both Patras and Athens. In Patras, during evening hours, PM1 concentrations were as high as 100 µg m−3, of which 85 % was OA. In Athens, the maximum hourly value observed during nighttime was 140 µg m−3, of which 120 µg m−3 was OA. Forty to 60 % of the average OA was due to biomass burning for both cities, while the remaining mass originated from traffic (12–17 %), cooking (12–16 %), and long-range transport (18–24 %). The contribution of residential wood burning was even higher (80–90 %) during the nighttime peak concentration periods, and less than 10 % during daytime. Cooking OA contributed up to 75 % during mealtime hours in Patras, while traffic-related OA was responsible for 60–70 % of the OA during the morning rush hour.
A method for the measurement of the water solubility distribution of atmospheric organic aerosols is presented. This method is based on the extraction of organic aerosols collected on filters, using ...different amounts of water and measurement of the corresponding water-soluble organic carbon concentration. The solubility distribution is then estimated using the solubility basis set. The method was applied on both ambient and source-specific aerosols. Approximately 60% of the atmospheric urban organic aerosol analyzed had water solubility higher than 0.6 g L–1. Around 10% of the fresh cooking organic aerosol had water solubility higher than 10 g L–1, while 80% of the total fresh cooking organic aerosol had solubility lower than 0.1 g L–1. The ambient measurements suggested that the solubility distributions are roughly consistent with the positive matrix factorization analysis results determined during the analysis of the high-resolution time-of-flight aerosol mass spectrometry data. Most of the oxidized organic aerosol appears to have water solubility above 0.6 g L–1, while the hydrocarbon-like organic aerosol and cooking organic aerosol have water solubility less than 0.002 and 0.1 g L–1, respectively. The biomass burning organic aerosol seems to have mostly intermediate solubility in water, between 0.04 and 0.6 g L–1. The proposed approach can quantify the solubility distribution in the 0.002–15 g L–1 range. Future extension of the method to higher solubility ranges would be useful for capturing the complete solubility range for atmospheric cloud condensation studies (0.1–100 g L–1).
Fine particulate matter (PM) originates from various emission sources and physicochemical processes. Quantification of the sources of PM is an important step during the planning of efficient ...mitigation strategies and the investigation of the potential risks to human health. Usually, source apportionment studies focus either on the organic or on the inorganic fraction of PM. In this study that took place in Patras, Greece, we address both PM fractions by combining measurements from a range of on- and off-line techniques, including elemental composition, organic and elemental carbon (OC and EC) measurements, and high-resolution Aerosol Mass Spectrometry (AMS) from different techniques. Six fine PM2.5 sources were identified based on the off-line measurements: secondary sulfate (34%), biomass burning (15%), exhaust traffic emissions (13%), nonexhaust traffic emissions (12%), mineral dust (10%), and sea salt (5%). The analysis of the AMS spectra quantified five factors: two oxygenated organic aerosols (OOA) factors (an OOA and a marine-related OOA, 52% of the total organic aerosols (OA)), cooking OA (COA, 11%) and two biomass burning OA (BBOA-I and BBOA-II, 37% in total) factors. The results of the two methods were synthesized, showcasing the complementarity of the two methodologies for fine PM source identification. The synthesis suggests that the contribution of biomass burning is quite robust, but that the exhaust traffic emissions are not due to local sources and may also include secondary OA from other sources.
Norpinic acid is a major semi-volatile oxidation product of α-pinene and β-pinene, two of the most important biogenic atmospheric volatile organic compounds. In this study we characterized the ...physicochemical properties of norpinic acid aerosol using a variety of techniques, and we investigated its reaction with OH radicals. The Aerosol Mass Spectrometer (AMS) spectrum of norpinic acid was characterized by a pronounced peak at m/z 82 (C5H6O+), which can be used as its chemical signature. The measured density of norpinic acid particles was 1.3 g cm−3. Its saturation concentration at 298 K was estimated to be equal to 8.9 μg m−3 using thermodenuder measurements and 12.8 μg m−3 using isothermal dilution. Its vaporization enthalpy was equal to 71 kJ mol−1. After reaction with OH radicals for an equivalent atmospheric period of 0.6–5 days under UV radiation and low RH, there were no noticeable changes in the AMS spectrum of the particles, while the wall-loss corrected mass concentration slightly decreased. This suggests that the atmospheric aging products of norpinic acid particles are quite similar to the parent molecule when measured by the AMS, and the aging reactions lead to a small change in particle mass concentration.
Abstract
Wildfires are a significant source of organic aerosol during summer, with major impacts on air quality and climate. However, studies in Europe suggest a surprisingly low (less than 10%) ...contribution of biomass burning organic aerosol to average summertime fine particulate matter levels. In this study we combine field measurements and atmospheric chemical transport modeling, to demonstrate that the contribution of wildfires to fine particle levels in Europe during summer is seriously underestimated. Our work suggests that the corresponding contribution has been underestimated by a factor of 4–7 and that wildfires were responsible for approximately half of the total OA in Europe during July 2022. This discrepancy with previous work is due to the rapid physicochemical transformation of these emissions to secondary oxidized organic aerosol with an accompanying loss of its organic chemical fingerprints. These atmospheric reactions lead to a regionally distributed background organic aerosol that is responsible for a significant fraction of the health-related impacts caused by fine particles in Europe and probably in other continents. These adverse health effects can occur hundreds or even thousands of kilometers away from the fires. We estimate that wildfire emissions are responsible for 15–22% of the deaths in Europe due to exposure to fine particulate matter during summer.
Two field campaigns were conducted in Patras during the summers of 2020 and 2021 in order to quantify the nucleation frequency in this area. Out of the 120 days with available measurements only 15 ...(12%) new particle formation events occurred. This low frequency is surprising given the high sunlight intensity, sulfur availability and low particle matter levels in the area during the study period. On the other hand, nucleation mode particles with average diameters of 20–40 nm appeared during the afternoon on 31% of the days. These particles did not grow, and the initial stages of their formation could not be observed. The corresponding days are traditionally classified as undefined events in similar studies. Our analysis suggests that these nucleation mode particles were not associated with emissions close to the measurement site but rather they had been formed several hours earlier in an area 100–150 km northeast of the field site and had grown significantly by the time they reached Patras. The air mass history suggested that new particle formation often took place in the vicinity of an area with significant agricultural activity and therefore high emissions of ammonia and amines. The term “transported events” can be used to better characterize these observed undefined days. The relatively high emissions of biogenic volatile organic compounds in western Greece, where Patras is located, did not appear to assist in the local formation of new particles.
•Infrequent summertime nucleation in a sunny Mediterranean area.•Frequent formation of particles 100 km away from the site and transport.•Evidence that ammonia or amines are involved in new particle formation.•Importance of agricultural activities in NPF.•Biogenic volatile organic compounds do not dominate NPF in this area.
The volatility distribution of ambient organic aerosol (OA) and its components was measured during the winter of 2013 in the city of Athens combining a thermodenuder (TD) and a High Resolution ...Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS). Positive Matrix Factorization (PMF) analysis of both the ambient and the thermodenuder AMS-spectra resulted in a four-factor solution for the OA, namely: hydrocarbon-like OA (HOA), biomass burning OA (BBOA), cooking OA (COA), and oxygenated OA (OOA). The thermograms of the four factors were analyzed and the corresponding volatility distributions were estimated using the volatility basis set (VBS). All four factors included compounds with a wide range of effective volatilities from 10 to less than 10−4 μg m−3 at 298 K. Almost 40% of the HOA consisted of low-volatility organic compounds (LVOCs) with the semi-volatile compounds (SVOCs) representing roughly 30%, while the remaining 30% consisted of extremely low volatility organic compounds (ELVOCs). BBOA was more volatile than the HOA factor on average, with 10% ELVOCs, 40% LVOCs, and 50% SVOCs. 10% of the COA consisted of ELVOCs, another 65% LVOCs, and 50% SVOCs. Finally, the OOA was the least volatile factor and included 40% ELVOCs, 25% LVOCs, and 35% SVOCs. Combining the volatility distributions and the O:C ratios of the various factors, we placed our results in the 2D-VBS analysis framework of Donahue et al. (2012). HOA and BBOA are in the expected region but also include an ELVOC component. COA is in similar range as HOA, but on average is half an order of magnitude more volatile. The OOA in these wintertime conditions had a moderate O:C ratio and included both semi-volatile and extremely low volatility components. The above results are sensitive to the assumed values of the effective vaporization enthalpy and the accommodation coefficient. A reduction of the accommodation coefficient by an order of magnitude or the reduction of the vaporization enthalpy by 20 kJ mol−1 results in the increase of the average volatility by half an order of magnitude.
•The volatility distribution of ambient organic aerosol components was measured.•Fresh biomass burning OA was the most volatile on average.•Oxygenated OA was the least volatile on average.•Cooking and biomass burning OA had intermediate average volatility.•All included some extremely low volatility and semi-volatile compounds.
Nucleation and subsequent growth are a major source of new particles in many environments, but the pollutants involved and the details of the corresponding processes are still under debate. While ...sulfuric acid has a major role in new particle formation under a lot of conditions, the role of ammonia, amines, and organic vapors is less clear. In most continental areas, new particle formation is quite frequent especially on relatively clean, sunny days when there is some sulfur dioxide available. In parts of the Eastern Mediterranean even if all the previous requirements are satisfied, new particle formation events are relatively rare during summertime.
The importance of dust and biomass burning episodes on the atmospheric concentration of water-soluble reactive phosphate (SRP) was determined in the eastern Mediterranean. SRP was measured with a new ...rapid real-time automated analytical system with a time resolution of a few minutes per sample and with an extremely low detection limit. The average atmospheric concentration of SRP during the sampling campaign was estimated at 0.35 ± 0.25 (median 0.30) nmol P m−3. The maximum concentration of SRP (3.08 nmol P m−3) was recorded during an intense dust episode, and was almost ten times higher than the campaign average, confirming that Saharan dust was an important primary source of bioavailable P to the eastern Mediterranean, especially during the spring period when 60% of the events occurred. Predicted increases in the frequency and intensity of dust storms in the area will enhance the role of the atmosphere as a source of bioavailable P for the Mediterranean marine ecosystem. During the warm period, when Northerly winds prevailed, biomass burning processes contributed significantly to soluble phosphorus delivered from atmospheric sources to the eastern Mediterranean. These inputs during warm periods are especially important for the Eastern Mediterranean, where biological productivity is strongly limited by nutrient availability.
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•Soluble reactive P was measured online with a time resolution of a few minutes.•Saharan dust is an important primary source of bioavailable P.•The acid dust enhances the dust aerosol contribution to the soluble reactive P.•Biomass burning contributes significantly to soluble P in the area during summer.
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