Rural Background Site Research Articles

Calculations of the conversion factor from organic carbon to organic matter for aerosol mass balance

Aerosol mass balance studies based on filter samples require a conversion factor to derive organic matter (OM) concentrations from organic carbon (OC) measurements from thermo-optical methods. This factor provides indirect insights on the molecular structure of OM needed in chemical transport models. Site- and season-specific ratios of OC to OM (fOM:OC) were calculated using data from five rural background sites in France between 2012 and 2021 by relating the unidentified chemical fraction in PM2.5 samples to thermo-optical OC concentrations. Further, multiple linear formulations were used to evaluate the impact of possible artefacts on the determination of fOM:OC. The resulting fOM:OC was then compared to other estimates derived from online aerosol mass spectrometry data, showing good agreement. The spatial and temporal variability in fOM:OC is discussed considering factors such as seasonality, meteorological conditions and the atmospheric oxidative potential. Linear-mixed effect models were formulated to quantitatively determine the drivers which influence the fOM:OC at the French rural background sites. Both ozone and relative humidity were variables with statistically significant effects on fOM:OC, indicating that differences in the contributions from both photooxidation and water content, explain the variability in fOM:OC observed at the French rural background sites. Site-specific fOM:OC yielded more accurate PM2.5 mass closure and are therefore recommended in mass-balance exercises. Accurate fOM:OC are critical to maintain consistency in OM time series, especially in cases where filter-based time series may be replaced by state-of-the-art online instrumentation.

Long-term measurements of aerosol composition at rural background sites in France: Sources, seasonality and mass closure of PM2.5

Fine particulate matter (PM2.5) was monitored at five rural background locations in France from 2012 to 2021. Annual PM2.5 ranged from 5 to 15 μg m−3, all sites repeatedly exceeding the 2021 annual World Health Organization guideline. Chemical speciation including organic and elemental carbon (OC, EC), secondary inorganic aerosols (SIA: NO3−, SO42−, NH4+) and other major water-soluble ions (Cl−, Na+, Mg2+, Ca2+, K+) were monitored on 24-h filters covering 14% of the year. A source apportionment of OM was undertaken based on fine potassium and using representative ratios for domestic biomass burning (BB) and fossil fuel (FF) emissions. The latter dominated the EC fraction (55–60%) while BB was the main primary source of OM (27–54%). The average mass balance of PM2.5 at the French rural background atmospheric sites was: secondary organic aerosol (18–35%), BB (17–27%), non-sea-salt sulphate (12–17%), nitrate (6–22%), ammonium (7–11%), FF (4–6%), mineral dust (3–9%) and sea salt (1–2%). Secondary aerosols were the main component of PM2.5 through all seasons, with SIA dominating in spring episodes. The contribution of OM to PM2.5 was larger at the southern sites whereas the contribution of SIA was larger at the northern sites. The mean OC/EC ratio and the good correlations between OC, EC, and fine potassium suggested that BB was the main primary source contributing to carbonaceous aerosols, 27–54% to total OM depending on the site; and also, to PM2.5 (17–27%). Stronger regulations of OM sources including BB, nitrate from combustion, and ammonium from agricultural sources are needed to reduce PM2.5 at rural background sites on an annual and episodic basis, respectively.

Elucidating the Effects of COVID-19 Lockdowns in the UK on the O3-NOx-VOC Relationship

The unprecedented reductions in anthropogenic emissions over the COVID-19 lockdowns were utilised to investigate the response of ozone (O3) concentrations to changes in its precursors across various UK sites. Ozone, volatile organic compounds (VOCs) and NOx (NO+NO2) data were obtained for a 3-year period encompassing the pandemic period (January 2019–December 2021), as well as a pre-pandemic year (2017), to better understand the contribution of precursor emissions to O3 fluctuations. Compared with pre-lockdown levels, NO and NO2 declined by up to 63% and 42%, respectively, over the lockdown periods, with the most significant changes in pollutant concentrations recorded across the urban traffic sites. O3 levels correspondingly increased by up to 30%, consistent with decreases in the [NO]/[NO2] ratio for O3 concentration response. Analysis of the response of O3 concentrations to the NOx reductions suggested that urban traffic, suburban background and suburban industrial sites operate under VOC-limited regimes, while urban background, urban industrial and rural background sites are NOx-limited. This was in agreement with the [VOC]/[NOx] ratios determined for the London Marylebone Road (LMR; urban traffic) site and the Chilbolton Observatory (CO; rural background) site, which produced values below and above 8, respectively. Conversely, [VOC]/[NOx] ratios for the London Eltham (LE; suburban background) site indicated NOx-sensitivity, which may suggest the [VOC]/[NOx] ratio for O3 concentration response may have had a slight NOx-sensitive bias. Furthermore, O3 concentration response with [NO]/[NO2] and [VOC]/[NOx] were also investigated to determine their relevance and accuracy in identifying O3-NOx-VOC relationships across UK sites. While the results obtained via utilisation of these metrics would suggest a shift in photochemical regime, it is likely that variation in O3 during this period was primarily driven by shifts in oxidant (OX; NO2 + O3) equilibrium as a result of decreasing NO2, with increased O3 transported from Europe likely having some influence.

Evaluating Health Risks of Volatile Organic Compounds in Various UK Environments: Insights from Health Indices

The health risks of twelve volatile organic compounds (VOCs) across three sites in the UK were analysed across an 11-year period (2013–2023) using US EPA proposed health indices; Inhalation Unit Risk (IUR) and Reference Concentration (RfC) for carcinogenic and non-carcinogenic risk, respectively. Significant decreases in carcinogenic risk were observed over the study period for 1, 3-butadiene, with reductions of 63%, 36%, and 45% at urban traffic, suburban background and rural background sites, respectively. Similar decreases in the carcinogenic risk associated with benzene (52%, 28% and 27%) and toluene (50%, 38% and 51%) are found for the three site types, respectively. However, the carcinogenic risk of these three pollutants still exceeds the acceptable threshold of 1 × 10-6 at the urban traffic and suburban background sites, necessitating further emission control strategies. Conversely, the carcinogenic risk associated with isoprene has increased at the urban traffic site over the study period. The study revealed a decrease of 51%, 39% and 37% of the total non-carcinogenic risk at all three sites over the study period. The seasonal variations in carcinogenic and non-carcinogenic health risks of pollutants with anthropogenic origin exhibit winter maxima and summer minima. Moreover, diurnal variations of pollutants with anthropogenic origin demonstrate a bimodal distribution reflecting that of traffic flow, e.g., peaks around 08:00 LT and 18:00 LT, corresponding with rush hours. This trend demonstrates the influence of traffic sources supported by the characteristic species ratio whereby Toluene/Benzene (T/B) ratios were less than two (0.72, and 0.42 at suburban and rural background sites, respectively), illustrating the influence of vehicular emissions. Despite following the same bimodal trend suggesting the dominance of vehicular emission sources, mean T/B ratios at urban traffic sites were consistently above 2 for all years considered (average 2.76) suggesting other VOC sources are becoming more dominant at this site.

Decadal trends (2009–2018) in Saharan dust transport at Mt. Martano EMEP station, Italy

Saharan dust advections in the Mediterranean Basin are widely studied and subjected to specific regulations due to their impact on the air quality of European cities. As a natural phenomenon, their contribution to PM should be accurately quantified in order to correctly evaluate their impact in anthropized areas. The identification and quantification of Saharan dust advections should be carried out in rural regional background sites. However, there is a lack of suitable sites in Central and Southern Italy, despite its strategic positioning in the Central Mediterranean area. The rural regional background site of Monte Martano site can fill this gap. This study aims at characterising the 10 years climatology of dust at the Monte Martano (MM) site and integrate it in the wider Mediterranean Basin monitoring network. Monte Martano is barely affected by local emissions, with average PM10 concentration of 11.0 ± 7.4 μg m−3, and a marked seasonality compatible with the evolution of the planetary boundary layer (PBL) during the year. Saharan dust advections contribute for 45.9 days per year on average, with a dust load that accounts for 48% of the background PM10 value. The Saharan dust advections' frequency, duration and intensity were evaluated, and a clear seasonality was detected, with minimum probability in summer and long-lasting events mainly occurring in spring and autumn. The dust load calculation was performed with 3 different methods, the EU guideline method, the modified DIAPASON methodology specifically designed for Central Italy and the DREAM8b model. The comparison between the three methods showed a substantial overestimation of the dust load by the model, while the two experimental methods are in accordance (R = 0.97). In conclusion, the MM site has proven to be suitable for Saharan dust monitoring in Central Italy, providing a new insight in the Central Mediterranean Saharan dust observation network.

Comparison of personal exposure to black carbon levels with fixed-site monitoring data and with dispersion modelling and the influence of activity patterns and environment

BackgroundShort-term studies of health effects from ambient air pollution usually rely on fixed site monitoring data or spatio-temporal models for exposure characterization, but the relation to personal exposure is often not known.ObjectiveWe aimed to explore this relation for black carbon (BC) in central Stockholm.MethodsFamilies (n = 46) with an infant, one parent working and one parent on parental leave, carried battery-operated BC instruments for 7 days. Routine BC monitoring data were obtained from rural background (RB) and urban background (UB) sites. Outdoor levels of BC at home and work were estimated in 24 h periods by dispersion modelling based on hourly real-time meteorological data, and statistical meteorological data representing annual mean conditions. Global radiation, air pressure, precipitation, temperature, and wind speed data were obtained from the UB station. All families lived in the city centre, within 4 km of the UB station.ResultsThe average level of 24 h personal BC was 425 (s.d. 181) ng/m3 for parents on leave, and 394 (s.d. 143) ng/m3 for working parents. The corresponding fixed-site monitoring observations were 148 (s.d. 139) at RB and 317 (s.d. 149) ng/m3 at UB. Modelled BC levels at home and at work were 493 (s.d. 228) and 331 (s.d. 173) ng/m3, respectively. UB, RB and air pressure explained only 21% of personal 24 h BC variability for parents on leave and 25% for working parents. Modelled home BC and observed air pressure explained 23% of personal BC, and adding modelled BC at work increased the explanation to 34% for the working parents.ImpactShort-term studies of health effects from ambient air pollution usually rely on fixed site monitoring data or spatio-temporal models for exposure characterization, but the relation to actual personal exposure is often not known. In this study we showed that both routine monitoring and modelled data explained less than 35% of variability in personal black carbon exposure. Hence, short-term health effects studies based on fixed site monitoring or spatio-temporal modelling are likely to be underpowered and subject to bias.

Air-soil cycling of oxygenated, nitrated and parent polycyclic aromatic hydrocarbons in source and receptor areas

Polycyclic aromatic hydrocarbons (PAHs) and their oxygenated and nitrated derivatives, OPAHs and NPAHs, are semivolatile air pollutants which are distributed and cycling regionally. Subsequent to atmospheric deposition to and accumulation in soils they may re-volatilise, a secondary source which is understudied.We studied the direction of air-soil mass exchange fluxes of 12 OPAHs, 17 NPAHs, 25 PAHs and one alkylated PAH in two rural environments being influenced by the pollutant concentrations in soil and air, by season, and by land cover. The OPAHs and NPAHs in samples of topsoil, of ambient air particulate and gas phases and in the gas-phase equilibrated with soil were analysed by GC-APCI-MS/MS. The pollutants soil burdens show a pronounced seasonality, a winter maximum for NPAHs and PAHs and a summer maximum for OPAHs. One order of magnitude more OPAH and parent PAH are found stored in forest soil than in nearby grassland soil. Among a number of 3–4 ring PAHs, the OPAHs benzanthrone and 6H-benzo(c,d)pyren-6-one, and the NPAHs 1- and 2-nitronaphthalene, 9-nitrophenanthrene and 7-nitrobenz(a)anthracene are found to re-volatilise from soils at a rural background site in central Europe in summer. At a receptor site in northern Europe, net deposition of polycyclic aromatic compounds (PACs) prevails and re-volatilisation occurs only sporadic.Re-volatilisation of a number of PACs, including strong mutagens, from soils in summer and even in winter indicates that long-range atmospheric transport of primary PAC emissions from central Europe to receptor areas might be enhanced by secondary emissions from soils.

Positive matrix factorization of seasonally resolved organic aerosol at three different central European background sites based on nuclear magnetic resonance Aerosolomics data

Concentration data derived from 1H NMR analysis of the water-soluble organic compounds from fine aerosol (PM2.5) at three Central European background stations, Košetice, Frýdlant (both in the Czech Republic), and Melpitz (Germany), were used for detailed source apportionment analysis. Two winter and two summer episodes (year 2021) with higher organic concentrations and similar wind directions were selected for NMR analyses. The concentration profiles of 61 water-soluble organic compounds were determined by NMR Aerosolomics and a principal component analysis (PCA) was performed on this dataset. Based on the PCA results, 23 compounds were selected for positive matrix factorization (PMF) analysis in order to identify dominant aerosol sources at rural background sites in Central Europe. Both the PCA and the subsequent PMF analyses clearly distinguished the characteristics of winter and summer aerosol particles.In summer, four factors were identified from PMF and were associated with biogenic aerosol (61–78 %), background aerosol (9–15 %), industrial biomass combustion (7–13 %), and residential heating (5–13 %). In winter, only 3 factors were identified - industrial biomass combustion (33–49 %), residential heating (37–45 %) and a background aerosol (8–30 %). The main difference was observed in the winter season with a stronger contribution of emissions from industrial biomass burning at the Czech stations Košetice and Frýdlant (47–49 %) compared to the Melpitz station (33 %). However, in general, there were negligible differences in identified sources between stations in the given seasons, indicating a certain homogeneity in PM2.5 composition within Central Europe at least during the sampling periods.

A seven-year-based characterization of aerosol light scattering properties at a rural central European site

Our study investigates the temporal variability of aerosol light scattering properties measured at three wavelengths (total scattering coefficient, backscattering coefficient, Ångström scattering exponent, hemispheric backscattering ratio and asymmetry parameter) at the rural background site of the National Atmospheric Observatory Košetice over a period of over seven years (2012–2019). The influence of fog and cloudiness on aerosol light scattering properties (ASP), together with their comparison to particle number size distribution was also investigated. The overall medians of total scattering (σsp) and backscattering coefficient (σbsp), hemispheric backscattering ratio (b) and asymmetry parameter (g) measured at 550 nm and Ångström scattering exponent (SAE_450/700) were 35.20 Mm−1, 5.07 Mm−1, 0.14 and 0.57 and 1.82, respectively. σsp and g decreased by 2.05 Mm−1/year, and 0.009/year, respectively, whereas b increased by 0.004/year. The selected aerosol properties were strongly correlated with particle number, mass, area and volume concentrations in the 200–800 nm mode. A decrease in SAE_450/700 implies a shift towards larger particle sizes, and evolutions in b and g suggest a higher backscattering portion to total scattering. The highest σsp and σbsp levels were observed in the cold seasons together with higher concentrations of air pollutants (carbonaceous aerosol, SO2 and NOx). This could be explained by enhanced emissions from human activities such as domestic heating combined with the higher stability of the atmosphere (poor atmospheric dispersion). In the summer, decreases in particle size and higher rates of backscatter fraction were attributed to secondary organic aerosol (SOA) formation. The accumulation mode showed the strongest aerosol scattering potential, with SAE_450/700 values < 2. Aerosol light scattering was significantly higher during overcast and foggy days compared to fine, cloudy, partly cloudy and no-fog days, possibly due to the particle hygroscopic growth under high relative humidity (shift of particle size towards larger sizes), which in turn can lead to a lower aerosol backscattering fraction. Source identification linked the changes in ASP to the synoptic situation over Europe rather than to specific sources of pollution.

Assessing biases in atmospheric parameters for radiative effects estimation in tropical regions

Many studies highlight the importance of water vapor in tropical atmospheric radiative transfer calculations. However, limited research focuses on understanding the effects of biases in different atmospheric factors, such as pressure, temperature, water vapor, and ozone densities. These biases stem from various sources, including satellites, reanalysis data, and the standard TROPICAL atmosphere. This study explores how these biases influence estimates of two key things: atmospheric radiative forcing (ARF) and heating rate (HR) profiles over the tropical region. The study is undertaken at Gadanki, a rural background site in the tropics. It considers different situations - clear skies and those with aerosols - across different parts of the electromagnetic spectrum and throughout the seasons. Additionally, this study investigates how sensitive ARF and HR profiles are to biases in each of these atmospheric factors within specific spectral ranges. The study results show that the standard TROPICAL atmosphere often differs significantly from real-time measurements, leading to varied effects on radiation. Among the various factors, biases in water vapor density have the most substantial impact on ARF and HR, followed by biases in temperature. Moreover, longwave radiation is more sensitive to water vapor and temperature changes. This study emphasizes the importance of considering the exact state of the atmosphere, especially in tropical regions, when estimating ARF and HR. To improve estimates when real-time data isn't available, the study suggests combining data from the Microwave Limb Sounder (MLS) and the Atmospheric Infrared Sounder (AIRS), and using reanalysis data for broader assessments. It's also important to be cautious when using the TROPICAL atmosphere to analyze the radiative effects of aerosols.

Particle-size resolved aerosol levels of total and extractable platinum in urban and rural regions of Western Europe

In this study, we determined the levels of total and extractable platinum in size-resolved atmospheric aerosol (PM) samples obtained from roadside and background urban sites in each of six European cities (Amsterdam, Frankfurt, London, Milan, Stockholm, and Thessaloniki), as well as at three rural sites in northern, central and southern Europe. A Hi-Vol sampler was used to collect PM in three size classes (PM>7, PM7-3, PM3) which were characterized for total platinum and extractable platinum, using a suite of physiologically relevant extraction fluids – alveolar lung fluid (ALF), gambles saline, 0.07M HCl, and MQ (high purity, 18MΩ, water). The resulting large data set of Pt in ambient aerosols is one of the most extensive developed to date.Order-of-magnitude differences in air concentrations of total platinum were observed between urban sites, ranging from 2.4 to 45.6 pg/m3. Relatively consistent and low concentrations (0.9–4.9 pg/m3) of total platinum were observed at the rural background sites. Roadside canyon sites in London and Thessaloniki exhibited the highest concentrations. Levels of total platinum at urban background sites were similar across the cities (2.4–14.2 pg/m3) and were approximately ½ the levels measured at urban roadside/canyon sites. When total platinum concentrations were normalized to PM mass the range in air concentrations was substantially reduced to just 4-fold (mean of 129 ng/g at rural background sites to 532 ng/g, London/Thessaloniki). The majority of the total platinum was present in the fine (PM3) fraction, however the contribution of coarse particles (>7 μm and 7-3 μm) to total platinum was also very significant (>30% at nearly all sites).Median site class extractable platinum concentrations (total suspended particulate, TSP) were all below 1 pg/m3 except for the urban canyon sites in London and Thessaloniki (1.8–6.8 pg/m3). Rural background concentrations of extractable platinum (TSP) were especially low (0.05 pg/m3 in MQ and 0.13–0.25 pg/m3 in the other solvents). For the TSP, the MQ extractable fraction was 2.5–5.5% of total platinum across site classes and 6.1–21.1% across site classes for the other three solvents. Except for the most contaminated urban canyon sites (London and Thessaloniki) the differences in platinum extracted by the three non-MQ solvents was not significant when site class medians are compared; thus, 0.07M HCl may be used to address the putatively bioaccessible fraction of platinum in aerosol particulate matter.

A year-round observation of δ13C of dicarboxylic acids and related compounds in fine aerosols: Implications from Central European background site

Isotopic analysis of specific compounds in aerosols can be a useful tool when studying atmospheric processes. Here, we present the results of stable carbon isotope ratio (δ13C) measurements performed on a one-year set (n = 96, Sep. 2013–Aug. 2014) of dicarboxylic acids and related compounds in PM1 at a rural Central European background site, Košetice (Czech Republic).The most 13C enriched acid was oxalic (C2, annual average = −16.6 ± 5.0‰) followed by malonic (C3, avg. = −19.9 ± 6.6‰) and succinic (C4, avg. = −21.3 ± 4.6‰) acids. Thus, δ13C values decreased with an increase in carbon numbers. Azelaic acid (C9, avg. = −27.2 ± 3.6‰) was found to be the least 13C enriched.A comparison of δ13C of dicarboxylic acids from other background sites, especially in Asia, shows similar values to those from the European site. This comparison also showed that C2 is more 13C enriched at background sites than at urban ones. In general, we did not observe significant seasonal differences in δ13C values of dicarboxylic acids at the Central European station. We observed statistically significant differences (p value < 0.05) between winter and summer δ13C values solely for C4, glyoxylic acid (ωC2), glutaric acid (C5) and suberic acid (C8).The only significant correlations between δ13C of C2 and δ13C of C3 were found in spring and summer, suggesting that the oxidation of C3 to C2 is significant in these months with a strong contribution from biogenic aerosols. The strongest season-independent annual correlation was observed in δ13C values between C2 and C4, the two dominant dicarboxylic acids. Therefore, C4 appears to be the main intermediate precursor of C2 throughout the whole year.

Different approaches to explore the impact of COVID-19 lockdowns on carbonaceous aerosols at a European rural background site

To prevent the fast spread of COVID-19, worldwide restrictions have been put in place, leading to a reduction in emissions from most anthropogenic sources. In this study, the impact of COVID-19 lockdowns on elemental (EC) and organic (OC) carbon was explored at a European rural background site combining different approaches: − “Horizontal approach (HA)” consists of comparing concentrations of pollutants measured at 4 m a.g.l. during pre-COVID period (2017–2019) to those measured during COVID period (2020-2021); − “Vertical approach (VA)” consists of inspecting the relationship between OC and EC measured at 4 m and those on top (230 m) of a 250 m-tall tower in Czech Republic. The HA showed that the lockdowns did not systematically result in lower concentrations of both carbonaceous fractions unlike NO2 (25 to 36 % lower) and SO2 (10 to 45 % lower). EC was generally lower during the lockdowns (up to 35 %), likely attributed to the traffic restrictions whereas increased OC (up to 50 %) could be attributed to enhanced emissions from the domestic heating and biomass burning during this stay-home period, but also to the enhanced concentration of SOC (up to 98 %). EC and OC were generally higher at 4 m suggesting a greater influence of local sources near the surface. Interestingly, the VA revealed a significantly enhanced correlation between EC and OC measured at 4 m and those at 230 m (R values up to 0.88 and 0.70 during lockdown 1 and 2, respectively), suggesting a stronger influence of aged and long distance transported aerosols during the lockdowns. This study reveals that lockdowns did not necessarily affect aerosol absolute concentrations but it certainly influenced their vertical distribution. Therefore, analyzing the vertical distribution can allow a better characterization of aerosol properties and sources at rural background sites, especially during a period of significantly reduced human activities.

Measurement Report: Wintertime new particle formation in the rural area of the North China Plain – influencing factors and possible formation mechanism

Abstract. The high concentration of fine particles and gaseous pollutants makes polluted areas, such as the urban setting of North China Plain (NCP) of China, a different environment for new particle formation (NPF) compared to many clean regions. Such conditions also hold for other polluted environments in this region (for instance, the rural area of NCP), yet the underlying mechanisms for NPF remain less understood, owing to the limited observations of particles in the sub−3 nm range. Comprehensive measurements, particularly covering the particle number size distribution down to 1.3 nm, were conducted at a rural background site of Gucheng (GC) in the North China Plain (NCP) from 12 November to 24 December 2018. In total, five NPF events during the 39 effective days of measurements for the campaign were identified, with the mean particle nucleation rate (J1.3) and growth rate (GR1.3–2.4) being 22.0 cm−3 s−1 and 3.9 nm h−1, respectively. During these 5 d, NPF concurrently occurred at an urban site in Beijing. Sharing similar sources and transport paths of air masses arriving at our site to that of urban Beijing, we hypothesize that NPF events during these days in this region might be a regional phenomenon. The simultaneous occurrence of NPF in both places implies that H2SO4-amine nucleation, concluded for urban Beijing there, could probably be the dominating mechanism for NPF at our rural site. The higher concentration of sulfuric acid during many non-event days compared to that of event days indicates that the content of sulfuric acid may not necessarily lead to NPF events under current atmosphere. Only when the condensation sink or coagulation sink was significantly lowered, atmospheric NPF occurred, implying that condensation sinks (CSs) and coagulation sinks (CoagSs) are the dominating factors controlling the occurrence of NPF for the present rural environment of the NCP, which is quite similar to the feature seen in urban Beijing.

A yearlong monitoring campaign of polycyclic aromatic compounds and other air pollutants at three sites in Sweden: Source identification, in vitro toxicity and human health risk assessment

Air pollution is a complex mixture of gases and particulate matter (PM) with local and non-local emission sources, resulting in spatiotemporal variability in concentrations and composition, and thus associated health risks. To study this in the greater Stockholm area, a yearlong monitoring campaign with in situ measurements of PM10, PM1, black carbon, NOx, O3, and PM10-sampling was performed. The locations included an Urban and a Rural background site and a Highway site. Chemical analysis of PM10 was performed to quantify monthly levels of polycyclic aromatic compounds (PACs), which together with other air pollution data were used for source apportionment and health risk assessment. Organic extracts from PM10 were tested for oxidative potential in human bronchial epithelial cells. Strong seasonal patterns were found for most air pollutants including PACs, with higher levels during the winter months than summer e.g., highest levels of PM10 were detected in March at the Highway site (33.2 μg/m3) and lowest in May at the Rural site (3.6 μg/m3). In general, air pollutant levels at the sites were in the order Highway > Urban > Rural. Multivariate analysis identified several polar PACs, including 6H-Benzo[cd]pyren-6-one, as possible discriminatory markers for these sites. The main sources of particulate pollution for all sites were vehicle exhaust and biomass burning emissions, although diesel exhaust was an important source at the Highway site. In vitro results agreed with air pollutant levels, with higher oxidative potential from the winter samples. Estimated lung cancer cases were in the order PM10 > NO2 > PACs for all sites, and with less evident seasonal differences than in vitro results. In conclusion, our study presents novel seasonal data for many PACs together with air pollutants more traditionally included in air quality monitoring. Moreover, seasonal differences in air pollutant levels correlated with differences in toxicity in vitro.

Anthropogenic and biogenic tracers in fine aerosol based on seasonal distributions of dicarboxylic acids, sugars and related compounds at a rural background site in Central Europe

Water-soluble organic compounds in aerosols are considered as relevant indicators of atmospheric processes. Fine particulate matter (PM1) samples were collected at National Atmospheric Observatory Košetice (NAOK), a rural background site representative of Central Europe, from September 27, 2013 to August 9, 2014. The samples (n = 146) were analyzed for water-soluble dicarboxylic acids (hereafter referred to as diacids) and related compounds to identify their seasonal variations and origins. Based on the Positive Matrix Factorization (PMF) analysis, we identified 5 factors – 2 anthropogenic, 2 biogenic and 1 background factors.In winter, anthropogenic contributions dominated in total organic matter (OM). Typical tracers for the main winter anthropogenic factor 1, connected with biomass burning (BB), were anhydrosugars together with maleic (M), methylmaleic (mM) and methylsuccinic (iC5) acids. This BB factor accounted for 64.1 ± 14.3% of OM in winter (annual avg. 36.7 ± 27.4%). A secondary anthropogenic factor 2 was characterized by phthalic (Ph), terephthalic (tPh) and ketomalonic (kC3) acids, which we assigned to secondary combustion products. The contribution of anthropogenic factor 2 was at a similar level throughout the year (12.5 ± 10.1% in OM). Mainly in winter, although also in spring and autumn, was the characteristic formation of diacids by secondary aqueous phase reactions, typically accompanied by lower temperatures, global radiation and ozone (O3) concentrations, yet higher relative humidity (RH) and aerosol liquid water content (ALWC).In summer, contributions of biogenic origin dominated. Secondary organic aerosols (SOA) of biogenic origin were typically represented by malonic (C3), methylmalonic (iC4), 3-oxopropanoic (ωC3), 4-ketopimelic (kC7), 7-oxoheptanoic (ωC7), pimelic (C7) and suberic (C8) acids. The factor, named as Biogenic 1, was dominant in summer with a contribution of 40.3 ± 19.6% in OM, while in other seasons, its contribution was below 10%. This factor was mainly characterized by a relative summer increase in the concentrations of kC7 and ωC7 acids. The second biogenic factor 2, also significant in summer (36.8 ± 20.5%) and dominant in spring (34.9 ± 19.9%), was represented by primary sugars (fructose, galactose and sucrose), normal chain diacids (oxalic (C2) to azelaic (C9)) and their oxidative precursors (ωC3, 4-oxobutanoic (ωC4) and 5-oxopentanoic (ωC5) acids). The photochemical formation of SOA in the gas phase was characteristic mostly for the summer season, accompanied by higher temperatures, global radiation and O3 concentrations, and lower RH.Additionally, background factor was resolved, which represents compounds with no distinctive seasonal variation and can therefore be of both anthropogenic and biogenic origin and contained mainly less oxidized compounds (methylglyoxal (MeGly), glyoxal (Gly), glyoxylic acid (ωC2) and pyruvic acid (Pyr)).

Discovering oxidative potential (OP) drivers of atmospheric PM10, PM2.5, and PM1 simultaneously in North-Eastern Spain

Ambient particulate matter (PM) is a major contributor to air pollution, leading to adverse health effects on the human population. It has been suggested that the oxidative potential (OP, as a tracer of oxidative stress) of PM is a possible determinant of its health impact. In this study, samples of PM10, PM2.5, and PM1 were collected roughly every four days from January 2018 until March 2019 at a Barcelona urban background site and Montseny rural background site in northeastern Spain. We determined the chemical composition of samples, allowing us to perform source apportionment using positive matrix factorization. The OP of PM was determined by measuring reactive oxygen species using dithiothreitol and ascorbic acid assays. Finally, to link the sources with the measured OP, both a Pearson's correlation and a multiple linear regression model were applied to the dataset. The results showed that in Barcelona, the OP of PM10 was much higher than those of PM2.5 and PM1, whereas in Montseny results for all PM sizes were in the same range, but significantly lower than in Barcelona. In Barcelona, several anthropogenic sources were the main drivers of OP in PM10 (Combustion + Road Dust + Heavy Oil + OC-rich) and PM2.5 (Road Dust + Combustion). In contrast, PM1 -associated OP was driven by Industry, with a much lower contribution to PM10 and PM2.5 mass. Meanwhile, Montseny exhibited no clear drivers for OP evolution, likely explaining the lack of a significant difference in OP between PM10, PM2.5, and PM1. Overall, this study indicates that size fraction matters for OP, as a function of the environment typology. In an urban context, OP is driven by the PM10 and PM1 size fractions, whereas only the PM1 fraction is involved in rural environments.

Source attribution of nitrogen oxides across Germany: Comparing the labelling approach and brute force technique with LOTOS-EUROS

Millions of people are exposed to enhanced levels of nitrogen dioxide in urbanized areas, leading to severe health effects. Moreover, nitrogen oxides contribute to the formation of ozone and particulate matter, and as such have wider health related impacts. A substantial reduction of nitrogen oxides may offer considerable health benefits for the human society. As a first step, this requires a detailed understanding of source sector contributions to nitrogen oxide levels. Whereas many regions have information on the local (traffic) contributions, the source contributions to the rural and urban background levels are commonly not available. In this study we compared and evaluated the results of two source attribution techniques to quantify the contribution of 5 source sectors to background nitrogen oxide levels across Germany. The results of a labelling technique were compared to brute force simulations with variable emission reduction percentages. The labelled NO2 source contributions of the main sectors averaged for all urban background stations are road transport (45 ± 5%), non-road transport (24 ± 6%), energy & industry (20 ± 3%), households (10 ± 6%), and the remaining source sectors (1 ± 1%). For the brute force technique, the explained mass differs from the unperturbed baseline concentration after scaling the impact of each sensitivity simulation to 100%. The attributed concentration of NO2 is lower in urban background areas (−3 ± 5%) and larger in the rural background (4 ± 6%) than that of the labelling. Largest deviations up to −15% are calculated for the major cities along the Rhine and Main. The annual average overestimation for NO is about 53 ± 24% for urban and 40 ± 26% for rural background sites based on a 20% reduction of emissions. On shorter time scales the differences are larger. These deviations are caused by (the lack of) regime changes in the titration of ozone, most notably present at ozone-limiting conditions during nocturnal winter periods. As a consequence, the differences between the methodologies are larger for smaller emission reduction percentages applied in the brute force technique. Similarly, for small-sized emission source sectors larger deviations were found compared to large-sized sector categories. Hence, applying the brute force technique for the source attribution for a single sector should be avoided as there is no way to verify for consistency and quantify the error for the sector and total explained contribution. We recommend applying the labelling approach to estimate sector contributions in forthcoming studies for nitrogen oxides.

Nine-year trends of PM10 sources and oxidative potential in a rural background site in France

Abstract. Long-term monitoring at sites with relatively low particulate pollution could provide an opportunity to identify changes in pollutant concentration and potential effects of current air quality policies. In this study, 9-year sampling of PM10 (particles with an aerodynamic diameter below 10 µm) was performed in a rural background site in France (Observatoire Pérenne de l'Environnement or OPE) from 28 February 2012 to 22 December 2020. The positive matrix factorization (PMF) method was used to apportion sources of PM10 based on quantified chemical constituents and specific chemical tracers analysed on collected filters. Oxidative potential (OP), an emerging health metric that measures PM capability to potentially cause anti-oxidant imbalance in the lung, was also measured using two acellular assays: dithiothreitol (DTT) and ascorbic acid (AA). The sources of OP were also estimated using multiple linear regression (MLR) analysis. In terms of mass contribution, the dominant sources are secondary aerosols (nitrate- and sulfate-rich) associated with long-range transport (LRT). However, in terms of OP contributions, the main drivers are traffic, mineral dust, and biomass burning factors. There is also some OP contribution apportioned to the sulfate- and nitrate-rich sources influenced by processes and ageing during LRT that could have encouraged mixing with other anthropogenic sources. The study indicates much lower OP values than in urban areas. A substantial decrease (58 % reduction from the year 2012 to 2020) in the mass contributions from the traffic factor was found, even though this is not clearly reflected in its OP contribution. Nevertheless, the findings in this long-term study at the OPE site could indicate effectiveness of implemented emission control policies, as also seen in other long-term studies conducted in Europe, mainly for urban areas.

Chemically speciated mass size distribution, particle density, shape and origin of non-refractory PM&amp;lt;sub&amp;gt;1&amp;lt;/sub&amp;gt; measured at a rural background site in central Europe

Abstract. Seasonal variability of non-refractory PM1 (NR-PM1) was studied at a rural background site (National Atmospheric Observatory Košetice – NAOK) in the Czech Republic to investigate the effect of regional and long-range atmospheric transport in central Europe. NR-PM1 measurements were performed by compact time-of-flight aerosol mass spectrometry (C-ToF-AMS), and the chemically speciated mass size distributions, density, shape, and origin were discussed. Average PM1 concentrations, calculated as the sum of the NR-PM1 and the equivalent black carbon (eBC) concentrations measured by an aethalometer (AE), were 8.58 ± 3.70 µg m−3 in summer and 10.08 ± 8.04 µg m−3 in winter. Organics were dominant during both campaigns (summer/winter: 4.97 ± 2.92/4.55 ± 4.40 µg m−3), followed by SO42-in summer (1.68 ± 0.81/1.36 ± 1.38 µg m−3) and NO3- in winter (0.67 ± 0.38/2.03 ± 1.71 µg m−3). The accumulation mode dominated the average mass size distribution during both seasons, with larger particles of all species measured in winter (mode diameters: Org: 334/413 nm, NO3-: 377/501 nm, SO42-: 400/547 nm, and NH4+: 489/515 nm) indicating regional and long-range transport. However, since the winter aerosols were less oxidized than the summer aerosols (comparing fragments f44 and f43), the importance of local sources in the cold part of the year was still enough to be considered. Although aged continental air masses from the south-east (SE) were rare in summer (7 %), they were related to the highest concentrations of PM1, eBC, and all NR-PM1 species, especially SO42- and NH4+. In winter, slow continental air masses from the south-west (SW) (44 %) were linked to inversion conditions over central Europe and were associated with the highest concentrations among all NR-PM1 species as well as PM1 and eBC. Average PM1 material density (ρm) corresponded to higher inorganic contents in both seasons (summer: ∼ 1.30 g cm−3 and winter: ∼ 1.40 g cm−3). During episodes of higher mass concentrations ρm ranged from 1.30–1.40 g cm−3 in summer and from 1.30–1.50 g cm−3 in winter. The dynamic shape factors (χ) decreased slightly with particle mobility diameter (Dm) in both seasons. This study provides insights into the seasonal effects and air mass variability on aerosol particles, focusing on episodes of high mass and number concentrations measured at a central European rural background site.