Assessing the role of the chemical composition of particulate matter and its impact on air quality and climate in urban and non-urban areas

Deterioration in air quality and increased damage to ecosystems caused by emissions and subsequent depositions of pollutants are one of the main environmental problems. Of the various substances, particulate matter (PM) affects the environment most comprehensively, due to the diversity of emission sources and formation mechanisms, and the resulting variation in chemical composition and particle size. In recent years, particular attention has been paid to fractions of fine particulate matter - PM2.5 and PM1 (particles with aerodynamic diameter ≤ 2.5 μm and 1.0 μm, respectively), primarily because of the health effects they may cause. Moreover, fine particles are capable of persisting in the air for a long time, are carriers of various hazardous substances, and affect climate, ecosystems, materials, and visibility.

Diagnosis

The studies carried out by the Ambient Concentration Team of the Air Protection Department of the IPIŚ PAN (Institute of Environmental Engineering, Polish Academy of Sciences – IEE PAS) over the past two decades have shown that one of the most important ways of assessing the contribution of particular types of emission sources to the recorded PM concentrations is the examination of the physicochemical composition of selected fractions of atmospheric aerosols combined with the use of these results as data for a different class of receptor models [1,2]. Measurements of short-lived atmospheric constituents from both natural and anthropogenic sources are also gaining particular importance in climate impact assessment. Studies of this type of pollution require the use of advanced automatic apparatus, not included in the equipment of standard measurement stations. Within the project ACTRIS- IMP - Infrastructure for studying aerosols, clouds and trace gases, in which a consortium of national research institutions participates, technical and organizational premises of a new subsystem for studying the atmosphere has been developed. In Europe, monitoring of the physicochemical composition of the atmosphere is carried out in national networks (e.g. AURN (for Atmospheric Urban and Rural Network) in the UK, PMŚ (State Environmental Monitoring) in Poland) and/or international networks (e.g. WMO/GAW (for World Meteorological Organization - Global Atmosphere Watch), EEA, EMEP) [3]. In Poland, measurements of selected PM fractions have been conducted for many years within the air quality monitoring subsystem [4]. Although data on the full chemical composition of PM measured in the main monitoring networks in Europe are limited, a lot of information is provided by research projects and large infrastructure projects. A good example is the ACTRIS Research Infrastructure currently being developed in the country. The activities of the ACTRIS-PL consortium are focused on several core areas, which perfectly fit into the strategy of the European Research Infrastructure, and at the same time this research relates to the main strands of the currently implemented and in the long-term research plans of the national units:

  • measurements of aerosols, which on the one hand are a poorly understood climatic factor and on the other hand, as air pollutants, affect the quality of human life,
  • studies of clouds and the interaction of aerosols with clouds and the impact of aerosol and cloud properties on the environment and climate,
  • modelling and forecasting of atmospheric processes.

The report presents selected results of the research activities of IPIŚ PAN in the context of developing research infrastructure in relation to the current issues of air quality and adaptation to climate change, including those conducted as part of the consortium's ACTRIS station in Racibórz in southern Poland. It is a particularly important area in the context of assessing the effects of transboundary flows of air pollutants (including secondary transformation products of the gaseous precursors) from the south-western regions of the EU.

Investigations into chemical composition of particulate matter

The chemical composition of aerosols determines the volatility, reactivity density and toxicity of its respective fractions [3]. The dominant components of particulate matter are carbon matter and ionic compounds. The total content of carbon material in PM - total carbon (TC), consists of elemental carbon (EC), inorganic carbon (IC) and organic carbon (OC), while in analytical methods EC and OC contents are usually examined. It is also possible to determine the temperature fractions of OC (OC1÷OC4, PC) and EC (EC1÷EC 4), which express the amount of OC and EC, released from the sample during its heating in helium stream (OC) and helium-oxygen atmosphere (EC), at given temperature steps [5]. Since the aforementioned fractions represent the fingerprints of emission sources, they have often been used in studies on the analysis of sources of fine particulate matter [e.g., 5]. Various analytical techniques are used to quantify OC and EC concentrations [6], and among them, the thermal-optical method is considered to be the reference method. This method allows measurements to be performed according to several standard temperature protocols that vary in temperature thresholds, their number and duration. The most commonly used protocols include NIOSH, IMPROVE_A and EUSAAR_2, the latter being the recommended standard method in Europe and already used by EMEP and ACTRIS (Aerosol, Clouds and Trace Gases Research Infrastructure).

Sources of primary organic carbon (POC) can be the processes of incomplete combustion of fossil fuels and biomass, mechanical processes (e.g. tire abrasion) and vegetation (including material from shredded plant waste), emissions from car engines [7,8]. Secondary organic carbon (SOC) is formed in the atmosphere in chain reactions of volatile organic compounds (VOCs) from natural and anthropogenic sources [9].

Along with elemental and organic carbon, inorganic ions account for the dominant share in the total PM mass of suspended particles [6]. In urban areas, the mass of sulfates and nitrates linked to dust may constitute up to 85% of the mass of all ions extracted in water and 15-55% of the total mass of fine particulate matter [10]. Inorganic ions form an important part of the so-called secondary inorganic aerosol (SIA), especially sulfates (SO42-), nitrates (NO3-) and ammonium ions (NH4+) [11]. This component significantly affects the concentrations and composition of fine PM, both in areas remote from the significant emission sources and in urban areas [12]. The intensity of formation of individual SIA components depends strongly on the concentration of gaseous precursors, atmospheric oxidants and neutralizing compounds, and the characteristics of already existing aerosol particles, including water content and aerosol acidity [3]. Moreover, many papers emphasized the considerable impacts of atmospheric conditions, especially air temperature and relative humidity, as well as the great importance of long-haul transport processes [3,13].

The results of the annual measurement campaign (2019) run by IPIŚ PAN at two sites in Racibórz (urban background - "SZKOŁA" ("SCHOOL"); non-urban background - "IMGW" ("IMWM")) (Figure 1), located in the Silesian Voivodeship (southern Poland), are discussed below. It was found that the average annual concentration of PM2.5, both at the suburban background site (26.61 µg∙m-3) and the urban site (25.73 µg∙m-3), slightly exceeded the permissible value for the average annual concentration of PM2.5 (25 µg∙m-3) [14]. Much worse living conditions affecting the residents of the analyzed area, related to PM2.5 exposure, occurred during the heating season when 90 (Racibórz - IMGW) and 100 (Racibórz - SZKOŁA) cases of exceeding the value recommended by the WHO for daily average PM2.5 concentration (25 µg∙m-3) were found [15]. In both locations, carbon aerosol was the dominant component of fine particulate matter, with PM2.5 contributions of ~45% and ~39%. OC and EC concentrations showed significant seasonal variability, as did PM2.5 concentrations, more pronounced for organic carbon. In addition to TC, ions represented a dominant contribution to the mass of fine particulate matter at the suburban background site and the urban site in Racibórz, with average shares (entire period) of ~37% and ~39%, respectively. Concentrations of all analysed ions varied during the studied period, however, similarly as in the case of PM2.5 and carbon matter, higher concentration levels of these substances were recorded during the heating season. Irrespective of the season, the dominance of sulphate (SO42-), nitrate (NO3-) and ammonium (NH4+) ions was evident, which together accounted (for the entire period) ~24% (IMGW) and ~26% (SCHOOL).


Figure 1. The comparison of the chemical composition of PM2.5 at two measurement stations in Racibórz (period: 2019).
(IMGW - suburban background; SZKOŁA - urban background)

Particulate matter chemical composition and episodes of elevated PM concentrations

Although air quality has improved significantly over the past two decades, the problem of exceeding PM2.5 and PM10 limit values remains unresolved in many areas of Europe [12]. Periods of elevated concentrations of PM and other air pollutants raise serious concerns due to their adverse effects on public health [5]. To better understand the occurrence of PM2.5 episodes of elevated concentrations, the results of an annual measurement campaign carried out at a suburban background station in Racibórz (Silesian Province) were analyzed [3]. The PM2.5 concentrations and the concentrations and contributions of the main chemical components varied during the studied period, with a characteristic seasonal trend associated with fluctuations in the intensity of PM emissions and its precursors from anthropogenic sources, as well as the prevailing meteorological situation (Figure 2). A situation in which daily PM2.5 concentrations exceeded 50 µg∙m-3 was defined as an episode - 38 such exceedances were identified in 2018, including 7 longer periods. It was concluded that high PM2.5 concentrations in Racibórz and other similar stations in Poland were mainly caused by secondary organic carbon (SOC) and to a lesser extent nitrates. The results of the study provided valuable scientific information for the development of air protection strategies and programs, in which special attention should be paid to measures aimed at reducing emissions of PM gaseous precursors, especially non-methane volatile organic compounds ((NMVOCs) and nitrogen oxides (NOx). The possible impact of regional and long-haul transportation should also be considered, as it can significantly affect the quality of air, especially in non-urban areas.


Figure 2: Share of selected chemical components in PM2.5 from suburban background stations in Racibórz for different averaging periods

Carbon matter as the dominant chemical component of particulate matter

Figure 3 presents the summarized results of investigations into carbon matter conducted by IPIŚ PAN at selected measurement stations in southern Poland [16]. Samples of particulate matter from urban (Skawina, Trzebinia, Racibórz-Szkoła, Zabrze) and non-urban (Krynica, Rokitno, Racibórz-IMGW, Złoty Potok) background stations were analysed. The content of OC and EC was determined using the thermal-optical method with the Sunset Laboratory carbon analyser ("eusaar_2" protocol); the concentration of particular OC fractions (OC1÷OC4, PC) was also determined. The studies showed that the contribution of TC to PM was determined primarily by variations in the contribution of OC, with POC predominating over SOC, especially at rural background stations, which could be due to the combustion of low-quality fuels in local sources. Irrespective of the type of location, the dominant OC fractions were PC, followed by OC4 and OC2. Higher contributions of PC to OC during the heating season were observed at all considered measurement stations, suggesting that residential heating, including biomass burning and formation of secondary organic aerosol, may be an important source of PC. The relatively low spatial variability of OC4/OC and OC3/OC ratios may be indicative of different origins of these fractions associated with impacts from regional and long-haul transport. The lack of distinct seasonal variability for the proportion of OC3 and OC4 observed in Zabrze may indicate the influence of transport sources, including road dust and car exhaust. High content of OC2 and OC1 fractions in some areas was mainly related to the impact of local emission sources, such as industrial (e.g. Trzebinia, Skawina), coal and biomass combustion (e.g. Racibórz-C) or transport sources (e.g. Zabrze).

Figure 3. The share of EC and OC temperature fractions together with the share of secondary (SOC) and primary (POC) organic carbon in total carbon of the selected measuring stations of southern Poland
ALL – the entire measurement period; H - heating season; NH - non-heating season

Automatic measurements of soot concentrations in the Silesian Voivodeship

Carbon matter occurs in aerosols in many different chemical and physical forms. The term eBC (equivalent black carbon) means carbon aerosol, commonly known as soot, which can be quantified using an optical method [17]. Soot originates mainly from anthropogenic sources, including transportation, industries, and burning coal and biomasses for heating purposes. Soot particles also can absorb light - it is on this basis that they are measured in optical devices. Concerning the environment, the high light absorption efficiency of soot causes it to be recognized as a contributor to climatic change. Optical eBC analysis is based on the measurement of light absorption on an aerosol sample filter. One of the devices that monitors soot concentrations in atmospheric air is an instrument of the next generation, namely the AE33 model aethalometer. The AE33 aethalometer (Magee Scientific) is a highly sensitive automatic device that measures aerosol light absorption at seven different wavelengths (λ) ranging from near ultraviolet to near infrared (λ = 370, 470, 520, 590, 660, 880, and 950 nm). The aethalometer's built-in model allows estimation of the effects of fossil fuel combustion (eBCff) and biomass combustion (eBCbb) on total BC mass.

The results of eBC measurements made using AE33 in Zabrze from 2019 to 2020 are presented below. The results indicate that eBC, eBCff and eBCbb concentrations were within the range of 0.05-20.48 µg-m-3, 0.02-16.08 µg-m-3 and 0.02-4.40 µg-m-3, respectively (Table 1). There were distinct seasonal variations in eBCff and eBCbb concentrations during the analyzed measurement period (Figure 4).

Period
Indicator
BC
BCff
BCbb
The entire measuring period (4/1/2019-12/31/2020)
Avg
2,66
1,93
0,73
Min
0,05 (10/27,29-30/20;11/2-3/20)
0,02 (7/8/19)
0,02 (11/1/20)
Max
20,48 (1/16/20)
16.08 (1/16/20)
4,40 (1/16/20)
Non-heating season (4/1/2019-9/31/2019)
Avg
1,79
1,28
0,51
Min
0.40 (7/8/19)
0.32 (9/30/19)
0.06 (8/7/19)
Max
8.02 (4/17/19)
5.82 (4/17/19)
2.21 (4/17/19)
Heating season (10/1/2019-3/31/2020)
Med
4,70
3,39
1,32
Min
0.88 (2/11/20)
0.53 (2/11/20)
0.27 (10/3/19)
Max
20,48 (1/16/20)
16.08 (1/16/20)
4.40 (1/16/20)
Non-heating season (4/1/2020-9/31/2020)
Avg
1,00
0,71
0,29
Min
0,20 (7/13/20)
0,15 (7/12/20)
0,02 (6/21/20)
Max
3,57 (4/11/20)
2,45 (5/9/20)
1,29 (4/1/20)
Heating season (10/1/2020-12/31/2020)
Avg
3,65
2,77
0,88
Min
0,05 (10/27,29-30/20;11/2-3/20)
0,02 (11/2/20)
0,02 (11/1/20)
Max
14,85 (11/8/20)
12,08 (11/8/20)
3,85 (12/2/20)

Table 1. Descriptive statistics of the series of measurements of eBC, eBCff, eBCbb concentrations - daily concentrations during the entire period, divided into non-heating and heating seasons

Regardless of the season, the obtained results indicated significantly higher concentrations of eBCff (71-76% share in total eBC) compared to eBCbb (24-29%), which is consistent with numerous literature reports - long-term measurement trends confirm the dominant role of fossil fuel combustion in urban air pollution with carbon compounds [18,19]. The share of biomass combustion will be visible mainly in areas with compact rural development [20]. Biomass, mainly wood and waste are used among other things to fuel homes in stoves and fireplaces. Biomass burning is also a global phenomenon arising from forest fires. Currently, biomass burning is also recognized as one of the main sources of air pollution such as soot, organic particulates, free radicals and other substances that adversely affect human health, air quality, cloud formation processes and climatic changes [21].


Figure 4. Daily patterns of eBCff and eBCbb concentrations (µg·m−3) and their average contribution to total BC (%) recorded for the heating and non-heating seasons (April 2019 - December 2020)

Another instrument used to measure eBC concentrations is an aethalometer, model AE51, currently located at the Raciborz suburban station. This is a miniature instrument that measures the soot absorption coefficient for a wavelength of 880 nm. Figure 5 shows the results of measurements carried out in 2019-2020. The eBC concentrations at the background station in Racibórz (suburban area) were measured with the AE51. The eBC concentrations fell within the range of 0.14-3.62 µg·m−3 and, analogically to eBC concentrations from fossil fuel and biomass combustion, showed seasonal variability. In autumn and winter, eBC concentrations were elevated with a maximum value in December 2020.

Figure 5. Monthly patterns of eBC concentrations (µg·m−3) recorded from March 2019 to December 2020 in Racibórz.


Figure 6. The trend of eBC concentration changes at an urban background site in Zabrze, 2009-2020

At the measuring station in Zabrze, eBC concentrations were also measured using the MAAP 5012 (Multi-Angle Absorption Photometer) automatic analyzer. The MAAP measures the BC aerosol mass concentration at a single nominal wavelength of 637 nm [22,23]. Long-term measurements conducted in Zabrze indicate that the maximum average annual eBC concentration occurred in 2009 (Figure 6). After this period, there was a systematic decrease in eBC concentrations until 2013, which could suggest a "shutdown" of certain emission sources that significantly affected the measuring site. From 2013 to 2016, there was an upward trend in eBC concentrations which ranged from 3.93 to 4.79 µg·m−3. In the following years, the average annual eBC concentrations did not exceed 4 µg·m−3 and the minimum value (2.62 µg·m−3) was recorded in 2020. 

Solutions

There is currently a great demand for research aimed at understanding the impact of air pollutants on the climate and environment, the results of which will support air quality standards and help prioritize remedial and adaptation actions. The National Air Protection Programme (NAP) and the regional programmes (POPs) are aimed at efforts to gradually reduce PM emissions from major sources. The strategy presented in these programmes is based on imposing restrictions in the technical sphere, in the form of standards for fuel-burning devices not covered by local anti-smog resolutions (UAS). Neither KOP, POP and UAS indicate methods of controlling the implementation of the established principles of air protection policy, apart from the available results of the State Environmental Monitoring. Understanding the reasons for air quality non-compliance, as well as evaluating available and widely used tools for predicting air quality and its impacts, is critical to any decision-making process [24]. To reduce the effects of air pollution, especially in cities where most of the European population lives, it is important to define effective control strategies and corrective actions. Directive 2008/50/EC encourages the use of models in combination with data from fixed monitoring points in several applications. Developing new models and improving the quality of existing ones requires the provision of high-quality data on both spatial and temporal variability and vertical profile. The in situ and remote sensing methods planned within  ACTRIS, including studies of aerosol physicochemical composition, can fill an existing gap in data resources for model validation.

Episodes of high concentrations of air pollutants, including dust, are observed in most agglomerations and large cities of the world. During such episodes, concentrations of dust in the atmospheric air usually exceed the permissible levels of this pollutant several - to even a dozen times. Detailed knowledge of the formation, properties and transformations of aerosols is necessary to evaluate their impact on processes occurring in the atmosphere, climate and human health. An in-depth analysis of the chemical composition of dust will allow the estimation of sources of atmospheric aerosol emissions in an urban agglomeration. Obtaining reliable data on chemical composition will make it possible to rationalise air quality management under the POPs implemented and, at the same time, to assess the effects of implementing the so-called low-emission economy programmes under new EU investment priorities and the strategy of restricted traffic zones [25]. In the light of the research carried out at the IPIŚ PAN, it appears that the measurement of eBC using optical methods allows the tracking of structural changes in the emission of carbon-rich substances, in particular the share of fossil fuels and biomass in the energy mix.

Climate change adaptation programs and mitigation activities in the area of low emission reduction should be directly connected with the expansion of atmospheric research facilities. This will make possible the objective evaluation of the effects of implementing the programmes, improve the reliability of modelling and short-term forecasting, and establishes the foundation for personnel training and broad ecological education.

Authors:
dr inż. Krzysztof Klejnowski
dr Barbara Błaszczak
mgr Natalia Zioła
Department of Air Protection of IPIŚ PAN
www.ipis.pan.edu.pl 

Literature
[1]    Juda-Rezler K., Reizer M., Maciejewska K., Błaszczak B., Klejnowski K., Characterization of atmospheric PM2.5 sources at a Central European urban background site, Science of the Total Environment 713 (2020) 136729.
[2]    Claudio A. Belis, Bo R. Larsen, Fulvio Amato, Imad El Haddad, Olivier Favez, Roy M.Harrison, Philip K. Hopke, Silvia Nava, Pentti Paatero, André Prévôt, Ulrich Quass, Roberta Vecchi, Mar Viana, European Guide on Air Pollution Source Apportionment with Receptor Models, JRC REFERENCE REPORTS, 2014.
[3]    Barbara, B., Zioła, N., Mathews, B., Klejnowski, K., Słaby, K. (2020). The Role of PM2.5 Chemical Composition and Meteorology during High Pollution Periods at a Suburban Background Station in Southern Poland. Aerosol Air Qual. Res. 20, 2433–2447.
[4]    Strona internetowa Głównego Inspektoratu Ochrony Środowiska – Portal o jakości powietrza:
http://powietrze.gios.gov.pl/pjp/home (dostęp: 28.08.2018 r.)
[5]    DOS SANTOS D.A.M., BRITO J.F., GODOY J.M., ARTAXO P., Ambient concentrations and insights on organic and elemental carbon dynamics in São Paulo, Brazil, Atmospheric Environment, 2016, Vol. 144, 226–233.
[6]    Chow, J.C., Lowenthal, D.H., Chen, L.-W.A., Wang, X., Watson, J.G. (2015). Mass reconstruction methods for PM2.5: a review. Air Quality, Atmosphere & Health 8, 243–263.
[7]    Jones, A.M., Harrison, R.M. (2005). Interpretation of particulate elemental and organic carbon concentrations at rural, urban and kerbside sites. Atmospheric Environment 39, 7114–7126.
[8]    Gelencsér, A., May, B., Simpson, D., Sánchez-Ochoa, A. i inni (2007). Source apportionment of PM2.5 organic aerosol over Europe: Primary/secondary, natural/anthropogenic, and fossil/biogenic origin. Journal of Geophysical Research 112, D23S04, doi: 10.1029/2006JD008094
[9]    Mancilla, Y., Herckes, P., Fraser, M.P., Mendoza, A. (2015). Secondary organic aerosol contributions to PM2.5 in Monterrey, Mexico: Temporal and seasonal variation. Atmospheric Research 153, 348–359
[10]    Rogula-Kozłowska, W., Klejnowski, K., Rogula-Kopiec, P., Ośródka, L., Krajny, E., Błaszczak, B. i inni (2014b). Spatial and seasonal variability of the mass concentrations and chemical composition of PM2.5 in Poland. Air Quality, Atmosphere & Health 7, 41–58.
[11]    Błaszczak, B., Juda-Rezler, K., Rogula-Kozłowska, W., Reizer, M. i inni (2017). Ionic Composition of Fine Particulate Matter from Urban and Regional Background Sites in Poland. Environmental Engineering Science 34(4), 236–250.
[12]    Błaszczak, B., Widziewicz-Rzońca, K., Zioła, N., Klejnowski, K., Juda-Rezler, K. (2019). Chemical Characteristics of Fine Particulate Matter in Poland in Relation with Data from Selected Rural and Urban Background Stations in Europe. Applied Sciences 9(1), 98.
[13]    Reizer, M., Juda-Rezler, K. (2016). Explaining the high PM10 concentrations observed in Polish urban areas. Air Quality, Atmosphere & Health 9(5), 517–531.
[14]    Dyrektywa 2008/50/WE Parlamentu Europejskiego i Rady z dnia 21 maja 2008 r. w sprawie jakości powietrza i czystszego powietrza dla Europy (Dz. Urz. UE L. 152 z 11.06.2008, str.1)
[15]    WHO, 2013: World Health Organization. Health Effects of Particulate Matter. Policy implications for countries in eastern Europe, Caucasus and Central Asia; WHO Regional Office for Europe: Copenhagen, Denmark, 2013; ISBN 978-92-890-0001-7.
[16]    Błaszczak, B.; Mathews, B. (2020). Characteristics of Carbonaceous Matter in Aerosol from Selected Urban and Rural Areas of Southern Poland. Atmosphere 11, 687.
[17]    Contini, D., Vecchi, R., Viana, M. (2018). Carbonaceous Aerosols in the Atmosphere. Atmosphere 9, 181.
[18]    Putaud, J.P., Cavalli, F., Crippa, M. Long-Term Trends in Black Carbon from Biomass and Fossil Fuel Combustion Detected at the JRC Atmospheric Observatory in Ispra, EUR 29147 EN; JRC110502; Publications Office of the European Union: Luxembourg, 2018; ISBN 978-92-79-80976-7.
[19]    Zheng, H., Kong, S., Wu, F., Cheng, Y., Niu, Z., Zheng, S., Yang, G., Yao, L., Yan, Q., Zheng, M., et al. (2019). Intra-regional transport of black carbon between the south edge of the North China Plain and central China during winter haze episodes. Atmos. Chem. Phys. 19, 4499–4516.
[20]    Klejnowski K., Janoszka K., Czaplicka M. (2017). Characterization and seasonal variation of organic and elemental carbon and levoglucosan in PM10 in Krynica Zdroj, Poland. Atmosphere 8, 1– 13.
[21]    Janoszka, K., Czaplicka, M., 2019. Methods for the determination of levoglucosan and other sugar anhydrides as biomass burning tracers in environmental samples – A review. J. Sep. Sci. 42, 319-329.
[22]    Hyvärinen A.-P., Vakkari V., Laakso L., Hooda R.K., Sharma V.P., Panawar T.S., Beukes J.P., van Zyl P.G., Josipovic M., Garland R.M., Andreae M.O., Pӧschl U., Petzold A. (2013). Correction for a measurement artefact of the Multi-Angle Absorption Photometer (MAAP) at high black carbon mass concentration levels. Atmos. Meas. Tech., 6, 81-90.
[23]    Massling A., Nielsen I.E., Kristensen D., Christensen J.H., Sørensen L.L., Jensen B., Nguyen Q.T., Nøjgaard J.K., Glasius M., Skov H. (2015). Atmospheric black carbon and sulfate concentrations in Northeast Greenland, Atmos. Chem. Phys., 15, 9681-9692.
[24]    Miranda, A., Silveira, C., Ferreira, J., Monteiro, A., Lopes, D., Relvas, H., Borrego, C, Roebeling, P. (2015). Current air quality plans in Europe designed to support air quality management policies. Atmospheric Pollution Research 6, 434–443.
[25]    INSPEKCJA OCHRONY ŚRODOWISKA, Pyły drobne w atmosferze, Kompendium wiedzy o zanieczyszczeniu powietrza pyłem zawieszonym w Polsce, Biblioteka Monitoringu Środowiska Warszawa, 2016.