Heavy pollution episodes, transport pathways and potential sources of PM2.5 during the winter of 2013 in Chengdu (China)

Air mass concentration data from 8 environmental quality monitoring sites and meteorological data of Chengdu from 1 December 2013 to 28 February 2014 were used in this study. Chengdu suffered five continuous heavy pollutions during this winter due to the basin terrain and the meteorological conditions of low wind speed, low precipitation and high relative humidity. Analysing the hourly resolution time series of pollutants' concentrations, variation of PM_2.5 in the urban area followed a growing "saw-tooth cycle" pattern during the heavy pollution, with a daily cycle of bimodal distribution. The massive letting-off of fireworks within a short period of time on the Eve of the Lunar New Year under the unfavourable diffusion conditions resulted in an extreme pollution event. The sharply rising Longmen-Qionglai Mountains to the west of the Sichuan Basin not only acted as a huge barrier to block the air mass from the east but also favoured the formation of a local circulation. The cluster analysis of back trajectories revealed that up to 77% of them came from the inner part of the Basin. Combining the concentration data of PM_2.5 with air mass back trajectories, a potential source contribution function (PSCF) model and a concentration-weighted trajectory (CWT) method were used to evaluate the transport pathways and sources over PM_2.5 of Chengdu, revealing that the main potential sources of PM_2.5 were located in southeast cities and the western margin of the Sichuan Basin. The result provided advice for the government to take measures in improving air quality.

Aerosol contributions at an urban background site in Eastern Mediterranean - Potential source regions of PAHs in PM10 mass

In this paper, two backward air mass trajectory-based models (Potential Source Contribution Function [PSCF] and Concentration Weighted Trajectory [CWT]) were combined, aiming to identify sources and factors defining the load of PM in the city of Limassol (Cyprus). The study also focused on the determination of atmospheric pathways enriching the aerosol phase of four carcinogenic Polycyclic Aromatic Hydrocarbons (PAHs): Benzo(a)pyrene (BaP), Benzo(a)anthracene (BaA), Benzo(b)fluoranthene (BbF) and Benzo(k)fluoranthene (BkF), in PM₁₀ mass. The analysis was performed on a 0.5°·0.5° resolution grid for the two-year period 2011-2012. During cold seasons, regional airflows triggered the accumulation of locally produced PM_2.5, while the impact of dust plumes originated from deserts in NE Africa, Syria and the Middle East, was apparent on PM_2.5 and principally on PM_COARSE levels. On the contrary, within warm seasons, weaker dust PM_COARSE contributions were detected in Limassol from areas in Egypt and Libya. Raised particulate-phase PAH concentrations in Limassol were clearly related to air parcels reaching Cyprus via continental areas. The use of outdated technologies for heating and transportation in Turkey and Syria, and fire events in central Turkey, are possible sources of exogenous PAHs throughout cold and warm period respectively. The influence of clean marine air masses dropped the levels of PAH compounds in all seasons.

Three year study of tropospheric ozone with back trajectories at a metropolitan and a medium scale urban area in Greece

Three years of hourly O3 concentration measurements from a metropolitan and a medium scale urban area in Greece: Athens and Ioannina respectively, were analyzed in conjunction with hourly wind speed/direction data and air mass trajectories, aiming to reveal local and regional contributions respectively. Conditional Probability Function was used to indicate associations among distinct wind directions and extreme O3 episodes. Backward trajectory clusters were elaborated by Potential Source Contribution Function on a grid of a 0.5°×0.5° resolution, in order to localize potential exogenous sources of O3 and its precursors. In Athens, an increased likelihood of extreme O3 events at the Northern suburbs was associated with the influence of SSW-SW sea breeze from Saronikos Gulf, due to O3 transportation from the city center. In Ioannina, the impacts of O3 conveyance from the city center to the suburban monitoring site were weaker. Potential O3 transboundary sources for Athens were mainly localized over Balkan Peninsula, Greece and the Aegean Sea. Potential Source Contribution Function hotspots were isolated over the industrialized area of Ptolemaida basin and above the region of Thessaloniki. Potential regional O3 sources for Ioannina were indicated across northern Greece and Balkan Peninsula, whereas peak Potential Source Contribution Function values were particularly observed over the urban area of Sofia in Bulgaria. The implemented methods, revealed local and potential transboundary source areas of O3, influencing Athens and Ioannina. Differences among the two cities were highlighted and the role of topography was emerged. These findings can be used in order to reduce the emission of O3 precursors.

Airborne heavy metals in two cities of North Rhine Westphalia - Performing inhalation cancer risk assessment in terms of atmospheric circulation

The main objective of this study was to examine the levels of four heavy metals (As, Cd, Pb and Ni) in PM₁₀ samples collected in two urban background stations in Dortmund and Bielefeld, in relation to atmospheric circulation. Pollution roses, Conditional Probability Function (CPF) roses and backward air mass trajectory clusters were used to identify air currents associated with the importation of PM₁₀ and of the included metal constituents. In addition, PM₁₀, NO₂, SO₂, O₃, As, Cd, Ni and Pb concentrations were analyzed by a Principal Component Analysis (PCA) to reveal major local emission sources of PM₁₀ metal content. Traffic was the main emitter of PM₁₀, As, Cd, and Pb in both cities, highlighting the existence of non-negligible lead quantities in unleaded gasoline, whilst nickel emissions were associated with heavy fuel oil combustion in industries and primarily for domestic heating. The created CPF roses and trajectory clusters were in good agreement, clearly revealing that eastern air currents enriched the locally produced PM₁₀ load with additional aerosols from Eastern Europe. The concentrations of arsenic and cadmium were also enhanced by the arrival of air parcels from the East, indicating the anthropogenic origin of the exogenous aerosols due to combustion. The induced cancer risk (CR_inh) for adults, due to inhalation of individual metal constituents, was also estimated in terms of atmospheric circulation, indicating higher risk in Dortmund than in Bielefeld. CR_inh values for arsenic exceeded the limit of 1 × 10^-6 in both cities, primarily during the influence of eastern circulation.

The covariance of air quality conditions in six cities in Southern Germany - The role of meteorology

This paper analyzed air quality in six cities in Southern Germany (Ulm, Augsburg, Konstanz, Freiburg, Stuttgart and Munich), in conjunction with the prevailing synoptic conditions. Air quality was estimated through the calculation of a daily Air Stress Index (ASI) constituted by five independent components, each one expressing the contribution of one of the five main pollutants (PM₁₀, O₃, SO₂, NO₂ and CO) to the total air stress. As it was deduced from ASI components, PM₁₀ from combustion sources and photochemically produced tropospheric O₃ are the most hazardous pollutants at the studied sites, throughout cold and warm periods respectively, yet PM₁₀ contribute substantially to the overall air stress during both seasons. The influence of anticyclonic high pressure systems, leading to atmospheric stagnation, was associated with increased ASI values, mainly due to the entrapment of PM₁₀. Moderate air stress was generally estimated in all cities however a cleaner atmosphere was detected principally in Freiburg when North Europe was dominated by low pressure systems. Daily events of notably escalated ASI values were further analyzed with backward air mass trajectories. Throughout cold period, ASI episodes were commonly related to eastern airflows carrying exogenous PM₁₀ originated from eastern continental Europe. During warm period, ASI episodes were connected to the arrival of regionally circulated air parcels reflecting lack of dispersion and accumulation of pollutants in accordance with the synoptic analysis.

Background concentrations of benzene, potential long range transport influences and corresponding cancer risk in four cities of central Europe, in relation to air mass origination

Benzene concentrations covering the three year period 2015-2017, were derived from four background monitoring stations located in Berlin (Germany), Budapest (Hungary), Mons (Belgium) and Torino (Italy), in order to calculate the corresponding Incremental Lifetime Cancer Risk (ILCR) of an average adult, associated with the inhalation of benzene. In addition, a cluster analysis of backward air mass trajectories was coupled with Potential Source Contribution Function (PSCF) model aiming to identify possible exogenous source regions of benzene affecting the four cities and also to allocate the ILCR in atmospheric circulation patterns. A potential health risk (ILCR>10^-6) from benzene exposure was estimated in all four cities. In Berlin and Mons, an enhanced fraction of the ILCR was associated with Southeast short range trajectories of slow moving air masses, which were also related to extreme long range transport episodes. Furthermore, increased benzene concentrations in Budapest were observed during the prevalence of short range Southwest airflows, whilst PSCF model isolated the transboundary emission sources in the industrialized North Italy. Long range trajectories of fast moving marine air masses from North Atlantic, not influenced by anthropogenic emissions, improved the benzene related air quality in Berlin and Mons due to dispersion. No long range transport effects were confirmed in Torino.

Decomposing the profile of PM in two low polluted German cities--mapping of air mass residence time, focusing on potential long range transport impacts

This paper aims to decompose the profile of particulates in Karlsruhe and Potsdam (Germany), focusing on the localization of PM potential transboundary sources. An air mass cluster analysis was implemented, followed by a study of air mass residence time on a grid of a 0.5° × 0.5° resolution. Particulate/gaseous daily air pollution and meteorological data were used to indicate PM local sources. Four Principal Component Analysis (PCA) components were produced: traffic, photochemical, industrial/domestic and particulate. PM2.5/PM10 ratio seasonal trends, indicated production of PMCOARSE (PM10-PM2.5) from secondary sources in Potsdam during warm period (WP). The residing areas of incoming slow moving air masses are potential transboundary PM sources. For Karlsruhe those areas were mainly around the city. An air mass residence time secondary peak was observed over Stuttgart. For Potsdam, areas with increased dwelling time of the arriving air parcels were detected particularly above E/SE Germany.

A review of multivariate analysis: is there a relationship between airborne particulate matter and meteorological variables?

Among statistical tools for the study of atmospheric pollutants, trajectory regression analysis (TRA), cluster analysis (CA), and principal component analysis (PCA) can be highlighted. Therefore, this article presents a systematic review of such techniques based on (i) air mass influences on particulate matter (PM) and (ii) the study of the relationship between PM and meteorological variables. This article aims to review studies that use TRA and to review studies that adopt CA and/or PCA to identify the associations and relationship between meteorological variables and atmospheric pollutants. Papers published between 2006 and 2018 and indexed by five of the main scientific databases were considered (ScienceDirect, Web of Science, PubMed, SciELO, and Scopus databases). PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) recommendations supported this systematic review. From the resulting most relevant papers, eight studies analyzed the influence of air mass trajectories on PM using TRA and twenty-one studies searched for the relationship between meteorological variables and PM using CA and/or PCA. A combination of TRA and time series models was identified as the possibility of future works. Besides, studies that simultaneously combine the three techniques to identify both the influence of air masses on PM and its relationship with meteorological variables are a possibility of future papers, because it can lead to a better comprehension of such a phenomenon.

Source characterization of volatile organic compounds in urban Beijing and its links to secondary organic aerosol formation

Volatile organic compounds (VOCs) are precursors for ozone and secondary organic aerosol (SOA) formation, thereby playing a vital role in atmospheric chemistry and urban air quality. To characterize the relationship between VOCs and SOA, organics both in gas and particulate phases were concurrently measured in urban Beijing. The VOCs and organic aerosol (OA) were apportioned into factors with different oxidation levels by applying the factorization analysis on their detailed mass spectra. Six factors of VOCs were identified, including four primary VOCs (PVOC) factors and two secondary VOCs (SVOC) factors. The PVOC factors dominated the total VOCs when the air mass originated in the cleaner northern areas, while SVOC factors dominated for polluted southern air masses. The normalized concentrations of PVOC and primary OA factors showed consistent diurnal variations regardless of air mass directions, owing to the relatively stable local emissions during the experimental period. This contrasted with the secondary factors due to more complex transformation processes. The traffic-related VOCs and solid fuel combustion VOCs negatively correlated with SOA, implying that they may have contributed to the SOA formation through photooxidation. The VOCs in lower oxidation levels were found to have poor correlations with the less oxidized SOA, whereas they correlated strongly to the more oxidized SOA. This implied that the less oxidized SOA may be in a transition state, where its production and loss rates were balanced. These served as products of VOCs oxidation and reactants of more oxidized SOA formation, playing important roles on the VOC to SOA transformation. The identified VOC emission sources and their photochemical production of SOA should be considered in air quality policy planning.

Distinct atmospheric patterns and associations with acute heat-induced mortality in five regions of England

The main objective of this paper was to identify possible acute heat-induced summer mortality in five regions of England namely the Yorkshire and the Humber, West Midlands, North East, North West and South East regions and reveal associations with specific air flows. For this purpose, backward air mass trajectories corresponding to daily episodes of increased temperatures were produced and divided to clusters, in order to define atmospheric pathways associated with warm air mass intrusions. A statistically significant at 95 % confidence interval increase in daily total mortality (DTMORT) was observed during the selected episodes at all five regions and thus, heat-induced mortality was indicated. The calculated raise was more intense in the West Midlands, North West and South East regions, whereas the results in the North East and Yorkshire and the Humber regions were less evident. Large fractions of thermal episodes, elevated average temperature values and higher average DTMORT levels were primarily associated with the short-medium range South West (SW) and/or East-South East (E-SE) trajectory clusters, suggesting relations among heat-induced mortality and specific atmospheric circulations. Short-medium length of SW and E-SE airflows, calculated by an application of Haversine formula along the centroid trajectory of each cluster, implies the arrival of slow moving air masses. Atmospheric stagnation could enhance human thermal stress due to low wind speed.