Urban Background Site Research Articles

Source apportionment of particle number size distribution at the street canyon and urban background sites

Abstract. Particle size is one of the key factors influencing how aerosol particles affect their climate and health effects. Therefore, a better understanding of particle size distributions from various sources is crucial. In urban environments, aerosols are produced in a large number of varying processes and conditions. This study intended to develop the source apportionment of urban aerosols by utilising a novel approach to positive matrix factorisation (PMF). The particle source profiles were detected in particle number size distribution data measured simultaneously in a street canyon and at a nearby urban background station between February 2015 and June 2019 in Helsinki, southern Finland. The novelty of the method is combining the data from both sites and finding profiles for the unified data. Five aerosol sources were found. Four of them were detected at both of the stations: slightly aged traffic (TRA2), secondary combustion aerosol (SCA), secondary aerosol (SecA), and long-range-transported aerosol (LRT). One of the sources, fresh traffic (TRA1) was only detected at a street canyon. The factors were identified based on available auxiliary data. Additionally, the trends of the found factors were studied, and statistically significant decreasing trends were found for TRA1 and SecA. A statistically significant increasing trend was found for TRA2. This work implies that traffic-related aerosols remain important in urban environments and that aerosol sources can be detected using only particle number size distribution data as input in the PMF method.

Atmospheric black carbon in the metropolitan area of La Paz and El Alto, Bolivia: concentration levels and emission sources

Abstract. Black carbon (BC) is a major component of submicron particulate matter (PM), with significant health and climate impacts. Many cities in emerging countries lack comprehensive knowledge about BC emissions and exposure levels. This study investigates BC concentration levels, identifies its emission sources, and characterizes the optical properties of BC at urban background sites of the two largest high-altitude Bolivian cities: La Paz (LP) (3600 m above sea level) and El Alto (EA) (4050 m a.s.l.), where atmospheric oxygen levels and intense radiation may affect BC production. The study relies on concurrent measurements of equivalent black carbon (eBC), elemental carbon (EC), and refractory black carbon (rBC) and their comparison with analogous data collected at the nearby Chacaltaya Global Atmosphere Watch Station (5240 m a.s.l). The performance of two independent source apportionment techniques was compared: a bilinear model and a least-squares multilinear regression (MLR). Maximum eBC concentrations were observed during the local dry season (LP: eBC = 1.5 ± 1.6 µg m−3; EA: 1.9±2.0 µg m−3). While eBC concentrations are lower at the mountain station, daily transport from urban areas is evident. Average mass absorption cross sections of 6.6–8.2 m2 g−1 were found in the urban area at 637 nm. Both source apportionment methods exhibited a reasonable level of agreement in the contribution of biomass burning (BB) to absorption. The MLR method allowed the estimation of the contribution and the source-specific optical properties for multiple sources, including open waste burning.

Sources and Variability of Greenhouse Gases over Greece

This study provides an overview of the atmospheric drivers of climate change over Greece (Eastern Mediterranean), focusing on greenhouse gases (GHG: carbon dioxide, CO2; methane, CH4; etc.). CO2 in Greece is mostly produced by energy production, followed by transport, construction, and industry. Waste management is the largest anthropogenic source of methane, accounting for 47% of total CH4 emissions, surpassing emissions from the agricultural sector in 2017, while the energy sector accounts for the remaining 10.5%. In situ simultaneous observations of GHG concentrations in Greece conducted at three sites with different topologies (urban background; Athens, regional background; Finokalia and free troposphere; and Helmos) during the last 5 years (2019–2023) showed increasing trends of the order of 2.2 ppm·yr−1 and ~15 ppb·yr−1 for CO2 and CH4, respectively, in line with the global trends. These increasing trends were found from both ground-based and satellite-based remote-sensing observations. Finally, during the lockdown period due to the COVID-19 global pandemic, a 58% reduction in CO2 levels was observed in the urban background site of Athens after subtracting the regional background levels from Finokalia, while the respective reduction in CH4 was of only the order of 15%, highlighting differences in emission sources.

Measurement report: Contribution of atmospheric new particle formation to ultrafine particle concentration, cloud condensation nuclei, and radiative forcing – results from 5-year observations in central Europe

Abstract. As an important source of sub-micrometer particles, atmospheric new particle formation (NPF) has been observed in various environments. However, most studies provide little more than snapshots of the NPF process due to their underlying observations being limited in space and time. To obtain statistically relevant evidence on NPF across various environments, we investigated the characteristics of NPF based on a 5-year dataset of the German Ultrafine Aerosol Network (GUAN). The results were also compared with observations in previous studies, with the aim to depict a relatively complete picture of NPF in central Europe. The highest NPF occurrence frequency was observed in regional background sites, with an average of about 19 %, followed by urban background (15 %), low-mountain-range (7 %), and high Alpine (3 %) sites. The annual mean growth rate between 10 and 25 nm varied from 3.7–4.7 nm h−1, while the formation rate with same size range 10–25 nm from 0.4 to 2.9 cm−3 s−1. The contribution of NPF to ultrafine particles (UFPs) was about 13 %, 21 %, and 7 % for the urban background, regional background, and low mountain range, respectively. The influence of NPF on cloud condensation nuclei (CCN) number concentration and the aerosol extinction coefficient for NPF days was the highest in mountainous areas. These findings underscore the importance of local environments when assessing the potential impact of NPF on regional climate in models, and they also emphasize the usefulness of a long-term aerosol measurement network for understanding the variation in NPF features and their influencing factors over a regional scale.

Health risks of PM2.5-bound metals at a street canyon: implication for traffic non-exhaust emissions

Traffic non-exhaust emissions are a significant source of toxic metals in fine particular matter (PM2.5), and thus pose adverse effects on human health. PM2.5-bound metals were sampled at a street canyon and urban background site during ozone and haze periods in Zhengzhou. Higher metal concentrations were observed at the street canyon than at the urban background site, which was more affected by traffic non-exhaust, oil combustion, and dust emissions. Consequently, PM2.5-bound metals may cause significant non-carcinogenic and carcinogenic hazards to residents at the street canyon. Traffic non-exhaust and oil combustion were the primary contributors to the non-carcinogenic and carcinogenic risk at the street canyon, respectively. Furthermore, the severe health risk of PM2.5-bound metals from traffic non-exhaust emissions will remain for a long time at street canyons. This work reveals the health risks from vehicles at street canyons, which is beneficial for further reduction of traffic-related emissions.

Dual-isotope ratios of carbonaceous aerosols for seasonal observation and their assessment as source indicators

Carbonaceous aerosols exhibit seasonal variations due to a complex interplay of emission sources, meteorological conditions, and chemical processes. This study presents the first year-round dual‑carbon isotopic analysis of carbonaceous aerosols in Northeastern Europe (Lithuania). The emphasis was placed on the processes affecting carbonaceous submicron particle (PM1) concentrations and their isotopic composition (δ13CTC, fc) during different seasons. Aerosol particles were collected in the two distinct sites: at an urban background site (Vilnius) and a coastal site (Preila). The concentrations of total carbon (TC) and black carbon (BC) varied both spatially and temporally. The annual average concentrations were 4 μg/m3 for TC and 2.3 μg/m3 for BC at the urban background site. They were considerably lower at the coastal site with 2.9 μg/m3 for TC and 0.74 μg/m3 for BC. The peak concentrations of TC and BC that occur during the cold season indicate a significant impact from residential heating. The δ13C in aerosols exhibited a distinct seasonal cycle with depleted δ13CTC values during the warm season (April–October). Through the integration of isotopic composition, contemporary carbon (fc), and BC source apportionment, we achieved precise predictions of isotopic parameter changes, encompassing pollution sources and the influence of meteorological parameters. To better understand the respective contributions of local and regional sources, air mass trajectories, wind patterns (speed and direction), and the polar conditional probability function (CPF) were studied in parallel. The study indicates that the isotopic composition of PM1 at both sites is primarily controlled by emission sources (local and regional), while meteorological conditions (temperature and mixing layer height) have less influence. These variations have important implications for regional air quality, climate dynamics, and public health, which are persistently subject to continuous research and monitoring.

Annual variation of source contributions to PM10 and oxidative potential in a mountainous area with traffic, biomass burning, cement-plant and biogenic influences

Toxicity of particulate matter (PM) depends on its sources, size and composition. We identified PM10 sources and determined their contribution to oxidative potential (OP) as a health proxy for PM exposure in an Alpine valley influenced by cement industry. PM10 filter sample chemical analysis and equivalent black carbon (eBC) were measured at an urban background site from November 2020 to November 2021. Using an optimized Positive Matrix Factorization (PMF) model, the source chemical fingerprints and contributions to PM10 were determined. The OP assessed through two assays, ascorbic acid (AA) and dithiothreitol (DTT), was attributed to the PM sources from the PMF model with a multiple linear regression (MLR) model. Ten factors were found at the site, including biomass burning (34, 40 and 38% contribution to annual PM10, OPAA and OPDDT, respectively), traffic (14, 19 and 7%), nitrate- and sulphate-rich (together: 16, 5 and 8%), aged sea salt (2, 2 and 0%) and mineral dust (10, 12 and 17%). The introduction of innovative organic tracers allowed the quantification of the PM primary and secondary biogenic fractions (together: 13, 8 and 21%). In addition, two unusual factors due to local features, a chloride-rich factor and a second mineral dust-rich factor (named the cement dust factor) were found, contributing together 10, 14 and 8%. We associate these two factors to different processes in the cement plant. Despite their rather low contribution to PM10 mass, these sources have one of the highest OPs per µg of source. The results of the study provide vital information about the influence of particular sources on PM10 and OP in complex environments and are thus useful for PM control strategies and actions.

Ultrafine particle measurements in New York State

Measurements of ultrafine particles (UFP) over several years were carried out across seven different locations in New York State. The locations include urban background sites (Queens College and Albany), near road sites (Queens, Buffalo and Rochester) and rural sites (Pinnacle State Park and Whiteface Mountain). UFP at the urban background and near road sites generally show highest concentrations in the morning during the early commute period. Concentrations decrease during the day but increase again in the afternoon or evening period. Weekday concentrations are higher than on weekends. UFP correlates well with traffic related co-pollutants black carbon (BC) and nitrogen oxides (NOx). At the rural locations, UFP concentrations show less variation during the day with highest concentrations in the early afternoon to late evening hours particularly in spring. Seasonally, UFP concentrations across urban background and near road sites, are highest in winter (Dec, Jan, Feb) and lowest in summer (Jun, Jul, Aug). The variation in UFP concentration with temperature, relative humidity and wind speed was investigated. At the Queens College site, particle number concentrations in six different size fractions were measured using a TSI 3031 instrument. Annual average UFP concentrations at Queens College were found to decrease over time consistent with emission control strategies.

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.

WSOC in accumulation mode aerosols: Distribution and relationship with BrC light absorption at an urban background site

This paper presents the outcomes of a one-month long campaign (Jan 11, 2021 to Feb 11, 2021) of size segregated particulate matter (PM) in the accumulation mode (AM). Samples were collected at an urban background station (southeastern Iberian Peninsula) using a micro-orifice uniform deposit impactor (MOUDI). PM mass and water-soluble organic carbon (WSOC) were subsequently measured. The main goals of this research were: (1) to explore differences in WSOC mass size distributions under different meteorological conditions and (2) to determine the most efficient size for light absorption by WSOC. For the second objective, measurements of absorption coefficients (σap,λ) were obtained by means of an Aethalometer (AE33). Significant differences in WSOC concentrations and σap,λ values during stagnation episodes compared to non-event days were observed. Increases in WSOC concentrations during these episodes were most likely associated with the photochemical production of secondary compounds (in small-size ranges of the AM) and with water uptake (in large-size ranges of the AM). The average σap,λ value during this type of event was 2.6 higher than for non-event days. No significant increases in WSOC levels were detected under Saharan dust events. The average contribution of BrC to light absorption at 370 nm was ∼35%, revealing a significant influence of BrC on the absorption process. High contributions from BrC to light absorption were associated with AAE values above 1.5 and, in general, with high WSOC concentrations. WSOC in the smallest size mode (0.25 μm) was mainly emitted from biomass burning (BB) and showed the highest light absorption efficiency.

The effect of mixed layer across air mass trajectory pathways on PM2.5 constituent levels: The case of a major urban center in the Eastern Mediterranean

Αn advanced three dimensional (3D) version of air mass Concentration Weighted Trajectory (CWT) model was applied, coupled with Mixed Layer Depth (MLD) estimations across the trajectory pathways. Three years daily PM2.5 composition measurements from an urban background site in Athens (Greece) were incorporated in the 3D-CWT model, to identify the atmospheric circulation patterns affecting PM2.5 constituent levels during cold (October 16th to April 15th) and warm (April 16th to October 15th) periods. The recirculation of local air masses inside the Mixed Layer (ML) during the cold period, was associated with accumulation of all PM2.5 constituents emitted from combustion sources (EC, OC, SO42−, NO3−, NH4+ and K+), whilst regional contributions of the same species were mainly associated with Northern airflows above the ML through Balkan Peninsula. In the cold period, transport of sea spray (Cl−, Na+ and Mg2+) and dust (Ca2+), from the Mediterranean and the Sahara desert respectively, was detected mainly through the ML, whilst sea salt from the Black Sea and dust from Balkan Peninsula were also transferred with Northern airflows above the ML. Contrariwise, transport from the Balkans area especially above the ML enriched the levels of all constituents of anthropogenic origin during the warm period, whilst the pattern of Saharan dust advections was also vertically extended above the ML. Conclusively, the implemented 3D-CWT model revealed a more detailed description of PM2.5 transport pathways in Athens, in comparison with the classic CWT model, by including the effect of MLD across the air mass trajectories.

Submicron aerosol pollution in Greater Cairo (Egypt): A new type of urban haze?

Greater Cairo, the largest megacity of the Middle East North Africa (MENA) region, is currently suffering from major aerosol pollution, posing a significant threat to public health. However, the main sources of pollution remain insufficiently characterized due to limited atmospheric observations. To bridge this knowledge gap, we conducted a continuous 2-month field study during the winter of 2019–2020 at an urban background site, documenting for the first time the chemical and physical properties of submicron (PM1) aerosols. Crustal material from both desert dust and road traffic dust resuspension contributed as much as 24 % of the total PM1 mass (rising to 66 % during desert dust events), a figure not commonly observed in urban environments. Our observations showed significant decreases in black carbon concentrations and ammonium sulfate compared to data from 15 years ago, indicating an important reduction in both local and regional emissions as a result of effective mitigation measures. The diurnal variability of carbonaceous aerosols was attributed to emissions emanating from local traffic at rush hours and nighttime open biomass burning. Surprisingly, semi-volatile ammonium chloride (NH4Cl) originating from local open biomass and waste burning was found to be the main chemical species in PM1 over Cairo. Its nighttime formation contributed to aerosol water uptake during morning hours, thereby playing a major role in the build-up of urban haze. While our results confirm the persistence of a significant dust reservoir over Cairo, they also unveil an additional source of highly hygroscopic (semi-volatile) inorganic salts, leading to a unique type of urban haze. This haze, with dominant contributors present in both submicron (primarily as NH4Cl) and supermicron (largely as dust) modes, underscores the potential implications of heterogeneous chemical transformation of air pollutants in urban environments.

Exploring the Formation of High Levels of Hydroxyl Dicarboxylic Acids at an Urban Background Site in South China

AbstractHydroxyl dicarboxylic acids (OHDCA) are ubiquitous in the atmosphere as an important constituent of secondary organic aerosol, yet the formation mechanisms remain unclear. At an urban background site on the coast of South China, we observed notable levels of OHDCA, with the highest concentration of malic acid (a typical OHDCA species) reaching 533 ng m−3. In the coastal air, the correlation between OHDCA and sulfate was better (R2 = 0.48) in the period when the relative humidity was higher and the sulfate size distribution was in a droplet mode, fitting the features of aqueous formation. In the short‐range continental air, a significant rise in OHDCA levels from morning through early afternoon (588 ng m−3) was observed under marked daytime increment of ozone that was corrected for titration loss (O3_corr, sum of ozone and nitrogen dioxide). In addition, good correlation between OHDCA and O3_corr was identified in this period, illuminating the role for gas‐phase photochemistry in regulating OHDCA formation. Therefore, the elevated OHDCA was likely attributed to aqueous photooxidation, and the dominant factors varied under different atmospheric conditions. The precursors of OHDCA could be derived from biogenic emissions, as indicated by the correlations of OHDCA with 2‐methylglyceric acid (bihourly data) and isoprene and monoterpenes (daily average data). However, anthropogenic aromatics might also be involved in OHDCA formation, especially in the short‐range continental air. The formation mechanisms probed through observational evidence will be an important reference for rectifying simulations of OHDCA and its impact on air quality and climate.

Characterization of water-soluble organic carbon absorption at an urban background site in the south-eastern Iberian Peninsula

Measurements of absorption coefficients (σap,λ) and carbonaceous components (OC, EC, WSOC and levoglucosan) in PM1 were conducted at an urban background site in southeastern Spain throughout 2021. The main goal of this research was to determine the contribution from different sources to WSOC light absorption (σWSOC). For this, σBrC,λ values were previously obtained. The mean contribution of BrC to total aerosol absorption was ∼29% at 370 nm, revealing a significant influence of BrC to light absorption in the study area. Assuming that BrC light absorption was from WSOC and WIOC, a multilinear regression (MLR) model was used to estimate σWSOC and σWIOC. Average values (mean ± SD) were very similar for both components: σWSOC,370 = 1.6 (±0.7) Mm−1 and σWIOC,370 = 1.9 (±0.7) Mm−1. Finally, the PMF technique coupled with MLR analysis was used to identify the sources of WSOC light absorption and estimate their contribution. Our findings point to biomass burning as the dominant source of σWSOC during the cold season, with a contribution of ∼37%. The Mineral Dust and Secondary Nitrate sources, that were not included in the model due to their low contribution to WSOC mass concentrations, accounted for a significant percentage of σWSOC during this period. Secondary organic aerosol was the major source during the warm season (∼56%), followed by traffic emissions (∼30%).

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.

Improving 3-day deterministic air pollution forecasts using machine learning algorithms

Abstract. As air pollution is regarded as the single largest environmental health risk in Europe it is important that communication to the public is up to date and accurate and provides means to avoid exposure to high air pollution levels. Long- and short-term exposure to outdoor air pollution is associated with increased risks of mortality and morbidity. Up-to-date information on present and coming days' air quality helps people avoid exposure during episodes with high levels of air pollution. Air quality forecasts can be based on deterministic dispersion modelling, but to be accurate this requires detailed information on future emissions, meteorological conditions and process-oriented dispersion modelling. In this paper, we apply different machine learning (ML) algorithms – random forest (RF), extreme gradient boosting (XGB), and long short-term memory (LSTM) – to improve 1, 2, and 3 d deterministic forecasts of PM10, NOx, and O3 at different sites in Greater Stockholm, Sweden. It is shown that the deterministic forecasts can be significantly improved using the ML models but that the degree of improvement of the deterministic forecasts depends more on pollutant and site than on what ML algorithm is applied. Also, four feature importance methods, namely the mean decrease in impurity (MDI) method, permutation method, gradient-based method, and Shapley additive explanations (SHAP) method, are utilized to identify significant features that are common and robust across all models and methods for a pollutant. Deterministic forecasts of PM10 are improved by the ML models through the input of lagged measurements and Julian day partly reflecting seasonal variations not properly parameterized in the deterministic forecasts. A systematic discrepancy by the deterministic forecasts in the diurnal cycle of NOx is removed by the ML models considering lagged measurements and calendar data like hour and weekday, reflecting the influence of local traffic emissions. For O3 at the urban background site, the local photochemistry is not properly accounted for by the relatively coarse Copernicus Atmosphere Monitoring Service ensemble model (CAMS) used here for forecasting O3 but is compensated for using the ML models by taking lagged measurements into account. Through multiple repetitions of the training process, the resulting ML models achieved improvements for all sites and pollutants. For NOx at street canyon sites, mean squared error (MSE) decreased by up to 60 %, and seven metrics, such as R2 and mean absolute percentage error (MAPE), exhibited consistent results. The prediction of PM10 is improved significantly at the urban background site, whereas the ML models at street sites have difficulty capturing more information. The prediction accuracy of O3 also modestly increased, with differences between metrics. Further work is needed to reduce deviations between model results and measurements for short periods with relatively high concentrations (peaks) at the street canyon sites. Such peaks can be due to a combination of non-typical emissions and unfavourable meteorological conditions, which are rather difficult to forecast. Furthermore, we show that general models trained using data from selected street sites can improve the deterministic forecasts of NOx at the station not involved in model training. For PM10 this was only possible using more complex LSTM models. An important aspect to consider when choosing ML algorithms is the computational requirements for training the models in the deployment of the system. Tree-based models (RF and XGB) require fewer computational resources and yield comparable performance in comparison to LSTM. Therefore, tree-based models are now implemented operationally in the forecasts of air pollution and health risks in Stockholm. Nevertheless, there is big potential to develop generic models using advanced ML to take into account not only local temporal variation but also spatial variation at different stations.

Evaluation of a Partector Pro for atmospheric particle number size distribution and number concentration measurements at an urban background site

Abstract. Particle number size distributions, total number concentrations and mean particle sizes have been measured for 70 d at an urban background site in Mülheim-Styrum, Germany, with a handheld Partector Pro of the first generation and a TSI mobility particle size spectrometer (MPSS). The aim of the study was to evaluate the performance of the Partector Pro against the MPSS. The results show that the size distributions, measured with the Partector Pro, agree with the MPSS mostly within ± 25 % for particle sizes between 10 and 113.5 nm, whereas higher, systematic differences were observed for larger particles. The measurement accuracy was shown to be dependent on the geometric mean diameter and the geometric standard deviation of the aerosol. Best results were found for the most abundant size distributions with geometric mean particle diameters ≥ 30 nm and geometric standard deviations larger than 1.8. The total number concentration, measured by the Partector Pro, was found to be in excellent agreement with the MPSS with a slope of the linear fit of 0.9977 and a regression coefficient of R2=0.9956. The agreement of the geometric mean particle diameter, determined with the Partector Pro and the MPSS was good but moderately dependent on the particle size distribution. For mean particle sizes between 20 and 50 nm, the bias was within ±15 %. Higher deviations of up to 30 % were observed when the geometric mean particle sizes exceeded 70 nm and when the geometric standard deviations exceeded approximately 2.7.

Meteorologically normalized spatial and temporal variations investigation using a machine learning-random forest model in criteria pollutants across Tehran, Iran

Investigating road traffic contribution to urban air pollution is helpful to determine traffic management approaches and environmental intervention policies that focus on better air quality. To this end, hourly average values of air pollutants collected from 2015 to 2021 from 20 monitoring sites including 10 traffic (TS) and 10 urban background (UB) sites in Tehran, Iran were retrieved. A machine learning-random forest (RF) model was applied to decouple the meteorology effects of the observed air pollutant values. The meteorologically normalized concentrations of air quality data were used for calculating the traffic increment and trend analysis. The seasonal component showed the greatest importance for predicting PM2.5 and PM10 and boundary layer heights (BLH) was the dominant explanatory variable for the predictions of CO, NO, NO2, and O3 concentrations. The overall annual average value of traffic increment during study period was found as PM10 (10.5 μg m−3), PM2.5 (0.19 μg m−3), NO (9.24 ppb), NO2 (3.67 ppb), NOx (15.6 ppb), and SO2 (0.33 ppb). Ozone indicates a traffic decrement in concentration (−0.70 ppb). The Theil-Sen estimated slopes showed meteorological normalized negative trends for PM2.5, PM10, CO, NO, NOx, and SO2, while meteorological normalized positive trends were observed for NO2 and O3. The PM10, CO, NO, NOx, and SO2 concentrations trends at the traffic sites that experience more anthropogenic emissions revealed greater reductions when emission interventions or control policies are used. The higher increase of NO2 at the UB sites than the traffic sites can be due to the weaker control policies, high traffic volume, higher number of diesel-fueled vehicles, and a higher NO to NO2 conversion because of the relatively high levels of temperature and O3. This quantitative summary provides useful information for decision-makers for evaluating the intervention policies related to road traffic pollutants.

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.

Assessing the role of atmospheric dispersion vs. emission strength in the southern Po Valley (Italy) using dispersion-normalised multi-time receptor modelling

In this paper, we applied the Dispersion Normalised Positive Matrix Factorisation (DN-PMF) approach recently proposed in the literature to provide a more realistic picture of the relative importance of emission strength vs. atmospheric dispersion conditions. The disentanglement of such effects is of great concern in pollution hot spots like the Po Valley (Italy), where particulate matter limit values are exceeded despite the existing abatement measures. To explore the potentiality of the DN-PMF approach – still scarcely applied in the literature – a well-chemically characterised PM1 (atmospheric particles with aerodynamic diameter <1 μm) dataset comprising samples collected at different time resolutions at an urban background site (Bologna) in the southern Po Valley was used. Indeed, it is well known that shallow mixing layers promote pollutant accumulation but this observation is not enough to exclude an enhancement of emission strength which could be tackled by appropriate abatement strategies.The source apportionment of sub-micron sized aerosols having a quite long atmospheric residence time in a complex environment like the Po Valley - which is also strongly impacted by secondary aerosol formation on a basin-scale - is generally quite challenging when using receptor models. Due to the availability of a huge dataset with variables having multiple time resolutions, in this work the DN-PMF was implemented in a multi-time resolution approach (MT) to achieve a better source identification and to gain knowledge about the relative importance of atmospheric dilution vs. emissions. A comparison between results obtained by the application of the regular multi time resolution (REG-MT) vs. the DN-MT approach is presented here for the five factors identified (nitrate-dominated, sulphate-dominated, biomass burning, mineral dust, and urban aerosol). The first interesting outcome is that REG-MT and DN-MT results do not point at significant differences in temporal patterns for aerosol components and sources impacting at the basin-scale (i.e. sulphate- and nitrate-dominated aerosol, biomass burning) thus suggesting that the diel modulation of these PM1 emissions is somehow masked by the stronger variability of the mixing layer. Conversely, contributions from local sources with more pronounced diel variation like traffic are quite well reproduced by DN-MT and the ambient concentrations are enhanced compared to REG-MT. This is an important piece of information highlighting that PM1 concentrations from local sources have been likely underestimated by REG-MT assessments.To our knowledge, this is one of the very few applications of DN-MT and the first one at a European site where the huge effort made to implement air pollution containment measures is still not very much effective in reducing PM levels; moreover, in this paper a detailed discussion about the possible interpretation of the output of DN-MT in terms of temporal patterns is reported.