We present 18 years (2001-2018) of aerosol measurements, including organic and elemental carbon (OC and EC), organic tracers (levoglucosan, arabitol, mannitol, trehalose, glucose, and ...2-methyltetrols), trace elements, and ions, at the Birkenes Observatory (southern Norway) - a site representative of the northern European region. The OC/EC (2001-2018) and the levoglucosan (2008-2018) time series are the longest in Europe, with OC/EC available for the PM.sub.10, PM.sub.2.5 (fine), and PM.sub.10-2.5 (coarse) size fractions, providing the opportunity for a nearly 2-decade-long assessment. Using positive matrix factorization (PMF), we identify seven carbonaceous aerosol sources at Birkenes: mineral-dust-dominated aerosol (MIN), traffic/industry-like aerosol (TRA/IND), short-range-transported biogenic secondary organic aerosol (BSOA.sub.SRT ), primary biological aerosol particles (PBAP), biomass burning aerosol (BB), ammonium-nitrate-dominated aerosol (NH.sub.4 NO.sub.3 ), and (one low carbon fraction) sea salt aerosol (SS).
The lockdown due to COVID-19 created a rare opportunity to examine the nonlinear responses of secondary aerosols, which are formed through atmospheric oxidation of gaseous precursors, to intensive ...precursor emission reductions. Based on unique observational data sets from six supersites in eastern China during 2019–2021, we found that the lockdown caused considerable decreases (32–61%) in different secondary aerosol components in the study region because of similar-degree precursor reductions. However, due to insufficient combustion-related volatile organic compound (VOC) reduction, odd oxygen (O x = O3 + NO2) concentration, an indicator of the extent of photochemical processing, showed little change and did not promote more decreases in secondary aerosols. We also found that the Chinese provinces and international cities that experienced reduced O x during the lockdown usually gained a greater simultaneous PM2.5 decrease than other provinces and cities with an increased O x . Therefore, we argue that strict VOC control in winter, which has been largely ignored so far, is critical in future policies to mitigate winter haze more efficiently by reducing O x simultaneously.
During winter 2013-2014 aerosol mass spectrometer (AMS) measurements were conducted for the first time with a novel PM2.5 (particulate matter with aerodynamic diameter ≤ 2.5 µm) lens in two major ...cities of China: Xi'an and Beijing. We denote the periods with visibility below 2 km as extreme haze and refer to the rest as reference periods. During the measurements in Xi'an an extreme haze covered the city for about a week and the total non-refractory (NR)-PM2.5 mass fraction reached peak concentrations of over 1000 µg m-3. During the measurements in Beijing two extreme haze events occurred, but the temporal extent and the total concentrations reached during these events were lower than in Xi'an. Average PM2.5 concentrations of 537 ± 146 and 243 ± 47 µg m-3 (including NR species and equivalent black carbon, eBC) were recorded during the extreme haze events in Xi'an and Beijing, respectively. During the reference periods the measured average concentrations were 140 ± 99 µg m-3 in Xi'an and 75 ± 61 µg m-3 in Beijing. The relative composition of the NR-PM2.5 evolved substantially during the extreme haze periods, with increased contributions of the inorganic components (mostly sulfate and nitrate). Our results suggest that the high relative humidity present during the extreme haze events had a strong effect on the increase of sulfate mass (via aqueous phase oxidation of sulfur dioxide). Another relevant characteristic of the extreme haze is the size of the measured particles. During the extreme haze events, the AMS showed much larger particles, with a volume weighted mode at about 800 to 1000 nm, in contrast to about 400 nm during reference periods. These large particle sizes made the use of the PM2.5 inlet crucial, especially during the severe haze events, where 39 ± 5 % of the mass would have been lost in the conventional PM1 (particulate matter with aerodynamic diameter ≤ 1 µm) inlet. A novel positive matrix factorization procedure was developed to apportion the sources of organic aerosols (OA) based on their mass spectra using the multilinear engine (ME-2) controlled via the source finder (SoFi). The procedure allows for an effective exploration of the solution space, a more objective selection of the best solution and an estimation of the rotational uncertainties. Our results clearly show an increase of the oxygenated organic aerosol (OOA) mass during extreme haze events. The contribution of OOA to the total OA increased from the reference to the extreme haze periods from 16.2 ± 1.1 to 31.3 ± 1.5 % in Xi'an and from 15.7 ± 0.7 to 25.0 ± 1.2 % in Beijing. By contrast, during the reference periods the total OA mass was dominated by domestic emissions of primary aerosols from biomass burning in Xi'an (42.2 ± 1.5 % of OA) and coal combustion in Beijing (55.2 ± 1.6 % of OA). These two sources are also mostly responsible for extremely high polycyclic aromatic hydrocarbon (PAH) concentrations measured with the AMS (campaign average of 2.1 ± 2.0-µg-m-3 and frequent peak concentrations above 10 µg m-3). To the best of our knowledge, this is the first data set where the simultaneous extraction of these two primary sources could be achieved in China by conducting on-line AMS measurements at two areas with contrasted emission patterns.
Isoprene-epoxydiols-derived secondary organic aerosol (IEPOX-SOA) can contribute substantially to organic aerosol (OA) concentrations in forested areas under low NO conditions, hence significantly ...influencing the regional and global OA budgets, accounting, for example, for 16–36 % of the submicron OA in the southeastern United States (SE US) summer. Particle evaporation measurements from a thermodenuder show that the volatility of ambient IEPOX-SOA is lower than that of bulk OA and also much lower than that of known monomer IEPOX-SOA tracer species, indicating that IEPOX-SOA likely exists mostly as oligomers in the aerosol phase. The OH aging process of ambient IEPOX-SOA was investigated with an oxidation flow reactor (OFR). New IEPOX-SOA formation in the reactor was negligible, as the OFR does not accelerate processes such as aerosol uptake and reactions that do not scale with OH. Simulation results indicate that adding ∼ 100 µg m−3 of pure H2SO4 to the ambient air allows IEPOX-SOA to be efficiently formed in the reactor. The heterogeneous reaction rate coefficient of ambient IEPOX-SOA with OH radical (kOH) was estimated as 4.0 ± 2.0 × 10−13 cm3 molec−1 s−1, which is equivalent to more than a 2-week lifetime. A similar kOH was found for measurements of OH oxidation of ambient Amazon forest air in an OFR. At higher OH exposures in the reactor (> 1 × 1012 molec cm−3 s), the mass loss of IEPOX-SOA due to heterogeneous reaction was mainly due to revolatilization of fragmented reaction products. We report, for the first time, OH reactive uptake coefficients (γOH = 0.59 ± 0.33 in SE US and γOH = 0.68 ± 0.38 in Amazon) for SOA under ambient conditions. A relative humidity dependence of kOH and γOH was observed, consistent with surface-area-limited OH uptake. No decrease of kOH was observed as OH concentrations increased. These observations of physicochemical properties of IEPOX-SOA can help to constrain OA impact on air quality and climate.
Organic aerosols (OA) derived from small-scale wood combustion emissions are not well represented by current emissions inventories and models, although they contribute substantially to the ...atmospheric particulate matter (PM) levels. In this work, a 29 m3 smog chamber in the ILMARI facility of the University of Eastern Finland was utilized to investigate the formation of secondary organic aerosol (SOA) from a small-scale modern masonry heater commonly used in northern Europe. Emissions were oxidatively aged in the smog chamber for a variety of dark (i.e., O3 and NO3) and UV (i.e., OH) conditions, with OH concentration levels of (0.5–5) × 106 molecules cm−3, achieving equivalent atmospheric aging of up to 18 h. An aerosol mass spectrometer characterized the direct OA emissions and the SOA formed from the combustion of three wood species (birch, beech and spruce) using two ignition processes (fast ignition with a VOC-to-NOx ratio of 3 and slow ignition with a ratio of 5).Dark and UV aging increased the SOA mass fraction with average SOA productions 2.0 times the initial OA mass loadings. SOA enhancement was found to be higher for the slow ignition compared with fast ignition conditions. Positive matrix factorization (PMF) was used to separate SOA, primary organic aerosol (POA) and their subgroups from the total OA mass spectra. PMF analysis identified two POA and three SOA factors that correlated with the three major oxidizers: ozone, the nitrate radical and the OH radical. Organonitrates (ONs) were observed to be emitted directly from the wood combustion and additionally formed during oxidation via NO3 radicals (dark aging), suggesting small-scale wood combustion may be a significant ON source. POA was oxidized after the ozone addition, forming aged POA, and after 7 h of aging more than 75 % of the original POA was transformed. This process may involve evaporation and homogeneous gas-phase oxidation as well as heterogeneous oxidation of particulate organic matter. The results generally prove that logwood burning emissions are the subject of intensive chemical processing in the atmosphere, and the timescale for these transformations is relatively short, i.e., hours.
In recent years, the Indian capital city of Delhi has
been impacted by very high levels of air pollution, especially during
winter. Comprehensive knowledge of the composition and sources of the
...organic aerosol (OA), which constitutes a substantial fraction of total
particulate mass (PM) in Delhi, is central to formulating effective public
health policies. Previous source apportionment studies in Delhi identified
key sources of primary OA (POA) and showed that secondary OA (SOA) played a
major role but were unable to resolve specific SOA sources. We address the
latter through the first field deployment of an extractive electrospray
ionization time-of-flight mass spectrometer (EESI-TOF) in Delhi, together
with a high-resolution aerosol mass spectrometer (AMS). Measurements were
conducted during the winter of 2018/19, and positive matrix factorization
(PMF) was used separately on AMS and EESI-TOF datasets to apportion the
sources of OA. AMS PMF analysis yielded three primary and two secondary
factors which were attributed to hydrocarbon-like OA (HOA), biomass burning
OA (BBOA-1 and BBOA-2), more oxidized oxygenated OA (MO-OOA), and less oxidized
oxygenated OA (LO-OOA). On average, 40 % of the total OA mass was
apportioned to the secondary factors. The SOA contribution to total OA mass
varied greatly between the daytime (76.8 %, 10:00–16:00 local time (LT)) and
nighttime (31.0 %, 21:00–04:00 LT). The higher chemical
resolution of EESI-TOF data allowed identification of individual SOA
sources. The EESI-TOF PMF analysis in total yielded six factors, two of
which were primary factors (primary biomass burning and cooking-related OA).
The remaining four factors were predominantly of secondary origin: aromatic
SOA, biogenic SOA, aged biomass burning SOA, and mixed urban SOA. Due to the
uncertainties in the EESI-TOF ion sensitivities, mass concentrations of
EESI-TOF SOA-dominated factors were related to the total AMS SOA (i.e.
MO-OOA + LO-OOA) by multiple linear regression (MLR). Aromatic SOA was the
major SOA component during the daytime, with a 55.2 % contribution to
total SOA mass (42.4 % contribution to total OA). Its contribution to
total SOA, however, decreased to 25.4 % (7.9 % of total OA) during the
nighttime. This factor was attributed to the oxidation of light aromatic
compounds emitted mostly from traffic. Biogenic SOA accounted for 18.4 %
of total SOA mass (14.2 % of total OA) during the daytime and 36.1 % of
total SOA mass (11.2 % of total OA) during the nighttime. Aged biomass
burning and mixed urban SOA accounted for 15.2 % and 11.0 % of total
SOA mass (11.7 % and 8.5 % of total OA mass), respectively, during the daytime and 15.4 % and 22.9 % of total SOA mass (4.8 % and 7.1 % of total OA mass), respectively, during the nighttime. A simple
dilution–partitioning model was applied on all EESI-TOF factors to estimate
the fraction of observed daytime concentrations resulting from local
photochemical production (SOA) or emissions (POA). Aromatic SOA, aged
biomass burning, and mixed urban SOA were all found to be dominated by local
photochemical production, likely from the oxidation of locally emitted volatile organic compounds (VOCs).
In contrast, biogenic SOA was related to the oxidation of diffuse regional
emissions of isoprene and monoterpenes. The findings of this study show that
in Delhi, the nighttime high concentrations are caused by POA emissions led
by traffic and biomass burning and the daytime OA is dominated by SOA, with
aromatic SOA accounting for the largest fraction. Because aromatic SOA is
possibly more toxic than biogenic SOA and primary OA, its dominance during
the daytime suggests an increased OA toxicity and health-related
consequences for the general public.
Residential coal combustion is a significant contributor to particulate urban air pollution in Chinese mega cities and some regions in Europe. While the particulate emission factors and the chemical ...characteristics of the organic and inorganic aerosol from coal combustion have been extensively studied, the chemical composition and nonmethane organic gas (NMOG) emission factors from residential coal combustion are mostly unknown. We conducted 23 individual burns in a traditional Chinese stove used for heating and cooking using five different coals with Chinese origins, characterizing the NMOG emissions using a proton transfer reaction time-of-flight mass spectrometer. The measured emission factors range from 1.5 to 14.1 g/kgcoal for bituminous coals and are below 0.1 g/kgcoal for anthracite coals. The emission factors from the bituminous coals are mostly influenced by the time until the coal is fully ignited. The emissions from the bituminous coals are dominated by aromatic and oxygenated aromatic compounds with a significant contribution of hydrocarbons. The results of this study can help to improve urban air pollution modeling in China and Eastern Europe and can be used to constrain a coal burning factor in ambient gas phase positive matrix factorization studies.
This study presents the molecular composition of organic aerosol (OA) using ultra-high-resolution mass spectrometry (Orbitrap) at an urban site in Central Europe
(Zurich, Switzerland). Specific ...source spectra were also analysed, including
samples representative of wood-burning emissions from Alpine valleys during
wood-burning pollution episodes and smog chamber investigations of woodsmoke, as
well as samples from Hyytiälä, which were strongly influenced by biogenic
secondary organic aerosol. While samples collected during winter in Alpine
valleys have a molecular composition remarkably similar to fresh laboratory
wood-burning emissions, winter samples from Zurich are influenced by more
aged wood-burning emissions. In addition, other organic aerosol emissions or
formation pathways seem to be important at the latter location in winter.
Samples from Zurich during summer are similar to those collected in
Hyytiälä and are predominantly impacted by oxygenated compounds with an H∕C
ratio of 1.5, indicating the importance of biogenic precursors for secondary organic aerosol
(SOA) formation at this location (summertime Zurich – carbon number 7.6, O:C
0.7;
Hyytiälä – carbon number 10.5, O:C 0.57). We could explain the strong
seasonality of the molecular composition at a typical European site by
primary and aged wood-burning emissions and biogenic secondary organic
aerosol formation during winter and summer, respectively. Results presented
here likely explain the rather constant seasonal predominance of
non-fossil organic carbon at European locations.
The role of polar regions is increasing in terms of
megatrends such as globalization, new transport routes, demography, and the use
of natural resources with consequent effects on regional and ...transported
pollutant concentrations. We set up the ERA-PLANET Strand 4 project “iCUPE
– integrative and Comprehensive Understanding on Polar Environments” to
provide novel insights and observational data on global grand challenges
with an Arctic focus. We utilize an integrated approach combining in situ
observations, satellite remote sensing Earth observations (EOs), and
multi-scale modeling to synthesize data from comprehensive long-term
measurements, intensive campaigns, and satellites to deliver data products,
metrics, and indicators to stakeholders concerning the environmental
status, availability, and extraction of natural resources in the polar areas.
The iCUPE work consists of thematic state-of-the-art research and the provision
of novel data in atmospheric pollution, local sources and transboundary
transport, the characterization of arctic surfaces and their changes, an assessment
of the concentrations and impacts of heavy metals and persistent organic
pollutants and their cycling, the quantification of emissions from natural
resource extraction, and the validation and optimization of satellite Earth
observation (EO) data streams. In this paper we introduce the iCUPE project
and summarize initial results arising out of the integration of comprehensive in
situ observations, satellite remote sensing, and multi-scale modeling in the
Arctic context.
Secondary organic aerosol (SOA) is an important contributor to fine particulate matter (PM) mass in polluted regions, and its modeling remains poorly constrained. A box model is developed that uses ...recently published literature parameterizations and data sets to better constrain and evaluate the formation pathways and precursors of urban SOA during the CalNex 2010 campaign in Los Angeles. When using the measurements of intermediate-volatility organic compounds (IVOCs) reported in Zhao et al. (2014) and of semi-volatile organic compounds (SVOCs) reported in Worton et al. (2014) the model is biased high at longer photochemical ages, whereas at shorter photochemical ages it is biased low, if the yields for VOC oxidation are not updated. The parameterizations using an updated version of the yields, which takes into account the effect of gas-phase wall losses in environmental chambers, show model–measurement agreement at longer photochemical ages, even though some low bias at short photochemical ages still remains. Furthermore, the fossil and non-fossil carbon split of urban SOA simulated by the model is consistent with measurements at the Pasadena ground site. Multi-generation oxidation mechanisms are often employed in SOA models to increase the SOA yields derived from environmental chamber experiments in order to obtain better model–measurement agreement. However, there are many uncertainties associated with these aging mechanisms. Thus, SOA formation in the model is compared to data from an oxidation flow reactor (OFR) in order to constrain SOA formation at longer photochemical ages than observed in urban air. The model predicts similar SOA mass at short to moderate photochemical ages when the aging mechanisms or the updated version of the yields for VOC oxidation are implemented. The latter case has SOA formation rates that are more consistent with observations from the OFR though. Aging mechanisms may still play an important role in SOA chemistry, but the additional mass formed by functionalization reactions during aging would need to be offset by gas-phase fragmentation of SVOCs. All the model cases evaluated in this work show a large majority of the urban SOA (70–83 %) at Pasadena coming from the oxidation of primary SVOCs (P-SVOCs) and primary IVOCs (P-IVOCs). The importance of these two types of precursors is further supported by analyzing the percentage of SOA formed at long photochemical ages (1.5 days) as a function of the precursor rate constant. The P-SVOCs and P-IVOCs have rate constants that are similar to highly reactive VOCs that have been previously found to strongly correlate with SOA formation potential measured by the OFR. Finally, the volatility distribution of the total organic mass (gas and particle phase) in the model is compared against measurements. The total SVOC mass simulated is similar to the measurements, but there are important differences in the measured and modeled volatility distributions. A likely reason for the difference is the lack of particle-phase reactions in the model that can oligomerize and/or continue to oxidize organic compounds even after they partition to the particle phase.
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