Insights into measurements of ambient air PM2.5 in China

Accepted Manuscript Title: Insights into Measurements of Ambient Air PM2.5 in China Authors: Zhipeng Bai, Jinbao Han, Merched Azzi PII: DOI: Reference:

S2214-1588(16)30065-4 http://dx.doi.org/doi:10.1016/j.teac.2017.01.001 TEAC 44

To appear in: Received date: Revised date: Accepted date:

13-12-2016 24-1-2017 25-1-2017

Please cite this article as: Zhipeng Bai, Jinbao Han, Merched Azzi, Insights into Measurements of Ambient Air PM2.5 in China, Trends in Environmental Analytical Chemistry http://dx.doi.org/10.1016/j.teac.2017.01.001 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Insights into Measurements of Ambient Air PM2.5 in China Zhipeng Bai a, Jinbao Han b, Merched Azzic,a a

State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research

Academy of Environmental Science, Beijing 100012, China b

College of Quality & Technical Supervision, Hebei University, Baoding 071002, China

c Commonwealth

Scientific and Industrial Research Organisation (CSIRO) Energy Flagship, 11

Julius Avenue, North Ryde, 2113 NSW, Australia

Abstract: Particulate matter with an aerodynamic diameter of 2.5 μm or less (PM2.5) is the main air pollutant in many countries. PM2.5 levels vary substantially over time and short distances, which directly affects the interpretation of data collected from reference stations. Although such data are usually accurate for one location at a certain time, they cannot be extrapolated to carry out complete spatial and temporal PM2.5 assessment. China’s varying geographies, climates and environment make it challenging to accurately measure ambient air PM2.5 levels. This paper describes the current state of PM2.5 pollution and standard/specifications of monitoring in China, reviews all available PM measurement techniques, highlights the advantages and limitations of the most widely used instruments, and discusses the related challenges. Based on our analysis of PM2.5 measurements, we suggest some ways to improve this measurement in China. In particular, suitable instruments need to be developed to accommodate different environments, climates and pollution levels across China. However, it is important to note that monitoring is merely a way to measure pollution levels, and not the main purpose of our research. The final purpose we have is creating a healthy and comfortable living environment for China’s residents. Keywords: Fine particles, air pollution, monitoring sites, measurement instruments, challenge. 1 Introduction Atmospheric particulate matter (PM) refers to a complex mixture of liquid and solid compounds, which are suspended in the air and can be detected and measured using monitoring instruments. PM consists of organic and inorganic compounds that can be emitted directly from combustion, exhaust emissions and industrial sources as primary emissions [1-3], or formed as secondary products resulting from non-linear atmospheric chemical reactions [3, 4]. The aerodynamic diameters of the suspended particles vary between a few nanometres to tens of micrometres, depending on their origins and their physical and chemical transformations. Particles with aerodynamic

diameters of less than 2.5 μm, designated as PM2.5, are likely to primarily originate from combustion and industrial sources, but also form through complex non-linear atmospheric chemical reactions [5] such as biogenic process forming secondary organic aerosols (SOAs). Numerous studies have concluded that PM2.5 is harmful to human health, e.g association with increase in mortality rate [6], hospitalisation due to respiratory diseases, disease of cardiovascular system [7-9] and/or reproductive system [10-12] and can play major roles in environmental processes, including the solar radiation budget, cloud formation and precipitation [13-19]. The PM2.5 particles can stay suspended in the air for several days and travel long distances downwind, until they come to rest by dry or wet deposition. Regulatory agencies are now introducing or updating regulations and policies to protect human health and the environment from PM2.5 pollution [20]. These regulations are regularly reviewed and updated to reflect new scientific health findings. These findings have drawn the attention of regulators to the need to collect continuous, accurate monitoring data of PM2.5 concentrations [21]. Meanwhile, research agencies are trying to develop advanced techniques for measuring PM2.5, and to deploy technologies for controlling primary emissions and the precursor emissions responsible for the production of secondary PM2.5 [22-27]. The available techniques and instruments use different scientific principles to collect and characterise PM2.5 data [28]. As a result, the collected data may depend on the instrument used, producing results that are not comparable for the same location. To ensure consistency in PM2.5 measurements, and to demonstrate the quality and comparability of PM2.5 data collected by diverse instruments, regulatory agencies have established standardised techniques, which should be fully implemented while collecting PM2.5 data. The reference method for monitoring PM2.5 is a manual, non-continuous method to determine PM mass [29, 30]. Continuous PM mass data are collected using technologies such as opacity monitors, light-scattering technologies, beta gauges and tapered-element oscillating microbalances (TEOM). Note that these techniques do not directly measure PM mass. In this paper, we review all available PM measurement techniques, including the reference method for monitoring PM2.5, and highlight the advantages and limitations of the most widely used instruments. Due to rapid urbanisation, concurrent with a sharp increase in energy consumption and motor-vehicle deployment in several major cities since the 1980s, PM2.5 pollution has become an alarming and serious concern in China. The 2015 environmental bulletin of China showed that the PM2.5 annual average concentration in 338 cities at prefecture level and above was 11–125 μm/m3, with an average of 50 μm/m3. Of these

cities, 265 (78.4%) have PM2.5 annual average concentrations exceeding the Grade II (35 μm/m3) of the Chinese Ambient Air Quality Standards (CAAQS). While PM2.5 pollution has emerged as an urgent problem for the Chinese Government that requires an immediate solution, Chinese research institutions have been concentrating on generating the fundamental and applied science that can be applied to resolve the problem. PM2.5 levels vary substantially over time and short distances. China’s different geographies, climates and environment make ambient air PM2.5 measurement in China a great challenge. In this paper, we describe the state of PM2.5 pollution and measurement in China, and discuss the challenges of PM2.5 monitoring. This information may be useful for researchers involved in PM2.5 studies, and for government agencies developing options to control and manage PM2.5 pollution in China. 2 Occurrence of PM2.5 in China In recent years, PM2.5 pollution in many Chinese cities has reached such extremely high levels that a special term, the ‘Chinese haze’, was created to describe the country’s air-quality problem [20]. 2.1 PM2.5 Pollution Level in China Despite the Chinese Government’s strict measures to improve air quality in major cities by relocating and controlling major sources of emissions, severe air pollution is still occurring. According to the annual report on the state of China’s environment [31], though the PM2.5 annual average concentration in the main regions (Beijing–Tianjin–Hebei, Yangtze River Delta and Pearl River Delta) and cities has been decreasing, it is still higher than the Grand II (35 μm/m3) of CAAQS (Fig. 1). These severe pollution episodes are more frequent during winter, due to a combination of coal combustion for house/building heating and prevailing meteorological conditions. Extremely high PM2.5 pollution episodes were not only observed in the megacities, but also in a range of Chinese cities at different times and seasons. This adds more complexity when exploring and defining proper solutions to control such pollution. In face of this complex situation, the Chinese Government is fully committed to reduce pollution below the current CAAQS levels while retaining focus on economic growth. Some relationships are apparent between PM2.5 concentration and topography [32]. China's landscapes vary significantly across the country, while the climate and environment differs from region to region because of its highly complex topography and land use. Huang et al. [33] investigated the 2013 haze pollution events with measurements at urban locations in Beijing, Shanghai, Guangzhou and Xi’an, located

respectively in the northern, eastern, southern and western regions of China. The daily average PM2.5 concentrations at Xi’an (345 μm/m3) were more than twice those of the other sites, followed by Beijing (159 μm/m3), Shanghai (91 μm/m3) and Guangzhou (69 μm/m3).

2.2 Chemical Characterisations of PM2.5 in China PM2.5 is a complex mixture of organic and inorganic substances that originate from different sources. The chemical composition of PM2.5 constituents are used to provide insight into the sources of compounds that require emission controls. Techniques used to characterise the chemical composition of PM2.5 samples collected on different media are shown in Table 1.

The physical growth and chemical composition of atmospheric fine particles are time-dependent, and driven by parameters such as the prevailing meteorological conditions and chemical reactions [41-43]. This situation adds additional complexities to the development of uniform, regional PM2.5 control options for a given airshed. Therefore, studies of PM physical and chemical properties are needed to understand the physical and chemical transformation processes that occur in the atmosphere[44]. PM2.5 chemical composition can vary substantially over geographical regions in China [45-47]. The variation can depend on pollution sources, including soil type and human activities, as well as meteorological conditions. For example, Zhao et al.[48] showed that secondary inorganic ions (sulfate, nitrate and ammonium), total carbon and secondary organic carbon were the significant components of PM2.5 in Shanghai. Lai et al.[49] showed that sulfate and organic matter were the major components of PM2.5 in rural Guangzhou, while Gao et al. [50] showed NO3−, SO42 −, NH4+, organic carbon (OC) and elemental carbon (EC) were the major chemical species of PM2.5 in Beijing. According to Tan et al.[51], the major constituents of PM2.5 were sulfate, OC, nitrate, ammonium and EC, and accounted for 50–88% of PM2.5 in Foshan city. We studied the characteristics of PM2.5 speciation in representative cities across China (Fig. 2). Crustal elements are the main chemical composition of PM2.5 in China. Organic matter is also an important chemical species of PM2.5 in China. Secondary particles, such as sulfate, nitrate and ammonium salt, have higher fractions in the eastern cities.

2.3 Sources of PM2.5 in China The formation of PM2.5 in China occurs by the same physical and chemical processes that have been described around the world, with the only difference being its high levels and growth. PM2.5 can be emitted directly from selected sources (primary PM), such as combustion and industry, or generated by gas-to-particle conversion in the atmosphere (secondary PM). Several techniques, including source apportionment modelling, isotope markers, trajectory modelling, are used to estimate the source of emissions [52-56]. We conducted source appointment studies in many cities in China (Fig. 3). Compared with developed countries, such as the United States [56, 57] and the United Kingdom [58, 59], dust accounts for a larger proportion of PM2.5 source apportionment in China, especially in western cities such as Xining. Secondary particles contributed more in megacities, such as Beijing, Wuhan and Chongqing. The contribution of the motor-vehicle exhaust to PM2.5 cannot be ignored in most cities of China, especially for megacities. The contribution of stationary sources, including coal combustion and industrial emissions, show a downward trend from north to south. Other recent published studies about source apportionment show that vehicle exhaust, coal combustion, crustal materials, industry, biomass burning and secondary particle formation are major sources, although the sources and their contribution to PM2.5 varied among different Chinese cities[60-67]. In coastal cities, such as Shenzhen[68] and Shanghai[69], sea salt is one of the major sources of PM2.5. These source apportionment studies provided valuable data for PM2.5 pollution control in China.

3 Standards/specifications about PM2.5 measurement in China Ambient air quality has been regulated in China since 1982. A standard for PM2.5 was established in 2012, when the new CAAQS (GB 3095-2012) was released. The new Chinese standards for PM2.5 limits are shown in Table 2, along with standards of other countries and organisations. Compared to the World Health Organization (WHO) and other countries’ standards, the Chinese standards are substantially less stringent. For example, the 24-hour limits in China (Grade II) are two times those in the United States, and three times those recommended by WHO. However, considering the current ambient levels of air pollutants, even achieving these relatively non-stringent new standards is very challenging.

To improve ambient air quality and protect people's health, a series of ambient air particle measurement standards and specifications have been issued since 2011 (Table 3). These documents are important guides to PM2.5 monitoring in China. In September 2013, China’s State Council issued the ‘Air Pollution Prevention and Control Action Plan’. This mandates 25, 20, 15 and 10% PM2.5 reductions from 2012 baseline annual average concentrations in the Beijing–Tianjin–Hebei region, the Yangtze River Delta region, the Pearl River Delta region and all other cities, respectively, by 2017. The declining proportion of PM2.5 concentration is one of the evaluation indicators for local governments. On 29 August 2015, China’s State Council released the final revision of the national Air Pollution Prevention and Control Law, which has been in force from 1 January 2016. The implementation of this law is a major step forward for governments determined to control ambient air pollution and protect public health. Monitoring networks were setup to collect data related to pollutants, and allow regulatory agencies to issue advisories and implement appropriate limits in target geographical locations when PM2.5 concentrations increase to unhealthy levels. China's ambient-air-quality monitoring network (AAQMN) consists of city stations, background stations, regional stations and key regional pre-warning platforms in almost all major regions. There are 1436 monitoring sites distributed in 338 cities, 14 background stations and 31 regional stations in rural areas[74]. These monitoring networks provide real-time, simultaneous measurements of PM2.5 across the entire country.

4 The Challenge of PM2.5 Measurement in China As mentioned, PM2.5 levels vary substantially over time and short distances. This conclusion directly affects the interpretation of data collected from reference stations. Such data are usually accurate, but cannot be extrapolated to carry out complete spatial and temporal PM2.5 assessment. The challenges facing the interpretation of PM2.5 data analysis can only begin to be resolved by achieving meaningful comparisons between data collected from different sites, times and instruments. 4.1 Optimised Monitoring Station Selection for PM2.5 Measurement The proper site selection of ambient-air-quality monitoring stations is a key factor for the collection of representative ambient PM2.5 data. The documents of HJ 664-2013 specify the principles and requirement for ambient-air-quality monitoring sites. Each

monitoring station’s location is scientifically determined to reflect the average level of local air quality in each target area. However, the layout of PM2.5 monitoring stations faces some challenges. First, the method for optimising a monitoring station’s site selection is not described in detail in HJ 664-2013. China is still at the initial stage of PM2.5 monitoring, and it is therefore difficult to provide historical monitoring data to optimise monitoring station selection. Second, existing PM2.5 monitoring stations are mainly concentrated in urban built-up areas, which cannot properly describe regional air-quality levels. Third, the collected data from existing PM2.5 monitoring stations may not be representative enough to develop PM2.5 emissions control options. The layout of a monitoring network should consider the collection of representative data and optimise the number of monitoring stations deployed in a given airshed, without affecting the quality of the data needed for further analysis. While monitoring for the study of variation in PM2.5 concentrations at a given site, it is also suggested to monitor for other pollutants, such as oxides of sulfur and nitrogen (SOx and NOx). Finally, the existing PM2.5 monitoring stations should be considered used for source apportionment studies, and the data obtained from these scattered locations should be combined to form a nationwide network, as has been achieved in the United States’ Interagency Monitoring of Protected Visual Environments (IMPROVE) and Chemical Speciation Monitoring Network (CSN) programs [44]. 4.2 PM2.5 Measurement Techniques The established PM2.5 monitoring program that monitor, sample and analyse PM2.5 uses different instruments, and can be successfully used for physical and chemical characterisation. The instruments produce information related to mass, number concentration, particle size distribution and chemical speciation. The monitoring is used by researchers to assess PM2.5 concentrations and temporal and spatial trends at selected locations, and to develop knowledge about the chemical and physical characteristics of PM2.5. Different methods for PM2.5 monitoring use different types of instruments. These methods can be classified as offline and online measurement. 4.2.1 Offline measurement Offline measurement, such as the gravimetric method, is the fundamental method of measuring PM mass concentration. In this method, atmospheric PM2.5 can be sampled by filtering air through a variety of collecting media, such as glass fibre, quartz, Teflon/polytetrafluoroethylene (PTFE) or PTFE-bonded glass fibre filters. For mass concentration determination using filter sampling techniques, the choice of filter requires the consideration of many factors, such as maintaining high efficiency

throughout a sampling run, meeting any pre-sampling requirements of the analytical procedure, cost, availability and ease of handling[75]. A careful choice will allow filters to be used for mass concentration measurements as well as for analysis of the chemical components of PM2.5, such as ionic species, EC and OC determinations. For example, Teflon filters are preferred for gravimetric determinations, because of their higher insensitivity to relative humidity during the weighing procedure [76]. However, if the beta-attenuation method is selected, glass and quartz-fibre filters can be used for mass determination. When sampling aims to determine the chemical composition of particles, the choice of membrane filter would depend on the type of chemical analysis to be carried out. When a complete chemical characterisation is needed, sampling using multiple substrates would normally be required. Teflon filters have low background levels of many species, including ions and elements, and are thus often used in chemical speciation. EC, OC and some carbon isotope determinations require high temperatures; in these cases, quartz-fibre filters are used as media to collect particles [77]. The advantages and limitations of the major filters used to collect PM2.5 are summarised in Table 4.

After selecting filters, sampling time segments should be considered to avoid overload. A careful investigation of year-round monitoring for PM2.5 mass concentration in Beijing [78] showed that Teflon filters, as recommended for gravimetric analyses, were reliable most of the time, but often failed under heavy load, with running time less than 18 h. All of the interruptions took place during polluted days, with PM2.5 exceeding the threshold of 75 μg/m3; 26% of these days were severe pollution (>250 μg/m3). Since high PM2.5 mass concentrations associated with high relative humidity might bring about the interruption, shorter sampling time segments should be set during periods of heavy pollution. Close monitoring of instruments is also necessary to allow fresh Teflon filters to be installed after interruptions occur. Other potential problems that may affect PM2.5 measurement by the gravimetric method include sampling flow rate, collection efficiency and weighing accuracy. There is no provision for the flow of the sampler, nor showing the effect of sampling rate to sampling accuracy in specifications and test procedures of PM2.5 sampling in China. Therefore, further studies focusing on the effect of different sampling flow on PM2.5 measurement should be conducted. 4.2.2 Online measurement

Routine PM2.5 measurements have been carried out using filter-based samplers. Analysis of the collected samples provided robust and accurate results on the nature of the particles[79]. However, this type of monitoring cannot provide the real-time information that is needed by regulators. In an ambient environment, filters may take weeks or even months to collect the substantial amount of material required for analysis. Long sampling periods can mask the concentration spikes of short or average duration, and affect the total average of pollution episodes. This makes it very impractical to gain information on changing air parcels during a day or over a week. Continuous, real-time instruments capable of measuring PM2.5 concentrations present an alternative method for routine filter-based methods. The time resolution provided by real-time PM2.5 monitors depends on the instrument, but is typically in the order of minutes. With this detailed time resolution, it would be possible for regulatory agencies to monitor peak concentration events that could then be correlated to data on health effects, especially for the analysis of acute health effects of ambient air pollution. Online instruments can be classified as either microbalance methods, beta-radiation attenuation methods (BAM) or light scattering methods (LSM). According to HJ 653-2013 and CAAQS, the specified method for PM2.5 automatic monitoring is TEOM and BAM. TEOM methods must also be combined with a filter dynamics measurement system (FDMS), because of the influence of semi-volatile material[80]. One of the challenges for PM online measurement in China is the imperfect technical specifications and requirements of PM2.5 automatic monitoring. Though several Chinese cities have carried out PM2.5 automatic monitoring for about 10 years, the instruments used vary because of the lack of a national certified or designated directory for PM2.5 automatic monitoring instruments. Hence, it is difficult to compare monitoring results between different cities and analyse monitoring data in depth. The second challenge is that methods and instruments for directly calibrating the accuracy of PM2.5 online measurement have not yet been developed. Some countries, such as the United States, European Union and Japan, have formulated a series of standards and specifications for PM2.5 monitoring methods, performance indicators and quality control. Only those methods and instruments meeting the standards and specifications can be used for PM2.5 measurement. Comparison with offline measurement is one way to test the reliability of PM2.5 automatic monitoring data [81]. The technical specifications and requirements of PM2.5 automatic monitoring instruments (for trial implementation) (2013 edition) was issued by the China National Environmental Monitoring Centre based on the results

of a study comparing BAMs and TEOMs with gravimetric measurements in different environments and conditions. The document defined three methods of PM2.5 online measurement, including BAM with dynamic heating system (BAM-DHS), BAM-DHS-LSM and TEOM-FDMS [82]. In comparison to the gravimetric method, BAM-DHS can reduce the effect of air moisture on monitoring to a certain extent, and BAM-DHS-LSM can improve the time resolution of monitoring data. However, both methods are prone to faults in areas of high humidity or where humidity varies greatly in a short period. The measurement results based on TEOM-FDMS are closer to those obtained using the gravimetric method, and are the best among the three online methods. Unfortunately, the high concentration of PM2.5 in many cities of China quickly blocks the filters used in the system, reducing their service life and increasing monitoring costs[82]. Yet another challenge of PM2.5 online measurement in China is that most of the instruments used for PM2.5 online measurement have been developed by other countries. Although they have been certified in their native countries, these instruments have a certain measurement range that decreases the measurement accuracy when the working circumstances change (e.g. from environments with low PM concentration to high PM concentration, from the plain to the plateau, or from environments with low humidity to high humidity). We compared PM2.5 measurement results from different online instruments produced by overseas and domestic manufacturers, regressing the results against the gravimetric method in Jinan (summarized in Table 5). Only the monitoring result derived from the domestic instrument achieved all the performance requirements of the regression analysis. Therefore, China needs to develop self-designed instruments with low-cost, portable, and low-power [83] for PM measurement that can adapt to the different environments found across China. In addition, the definition of ‘standard state’ varies in different countries. This will produce unconformity when converting PM2.5 concentration in the normal state to that in the standard state.

Using two measurement techniques that use different physical approaches can introduce challenges for analysing results. Differences in operation and data collection can lead to concentration discrepancies, resulting in confusion and uncertainties. Therefore, the results produced by different measurement techniques require careful interpretation, which must include a detailed awareness of the often complex assumptions and uncertainties associated with these techniques. During the

selection of fine-particle measurement techniques, it is important to determine the purpose of selecting the techniques, understand the main theoretical and fundamental principles of the technique’s basis, and be aware of the location where the instrument will be deployed, maintenance requirements, data storage and control. More details about PM2.5 measurement instruments and techniques is given by Amaral et al. [28]. 5 Conclusions and Recommendations for PM Measurement in China In this paper, we provides an overview of the current state of PM2.5 pollution in China, including its pollution level, chemical characterizations and sources. While the PM2.5 annual average concentration in main regions and cities has been decreasing since PM2.5 standard established in 2012, it is still a challenge for achieving the relatively non-stringent CAAQS. Organic matter is one of major chemical species of PM2.5 in China, though PM2.5 speciation compositions can vary substantially over geographical regions across China. Based on several source apportionment studies in recent years, the major PM2.5 sources in China have been identified to be vehicle exhaust, coal combustion, dust, industry, biomass burning, and secondary particle formation. There are many instruments available on the market for PM2.5 measurement. We also have reviewed and discussed the most widely used offline and online PM2.5 instruments in China, and highlighted insights into their advantages and limitations. The gravimetric method is necessary to assess compliance with PM2.5 target levels, while continuous monitoring data can be used to assess variability in PM2.5. While each method has advantages and disadvantages, a combination of various methods can overcome these difficulties. However, there are some challenges for PM2.5 monitoring in China. In particular, China need to develop suitable instruments which can adapt to different environments, climates and pollution levels across China, such as in dusty and low pressure environment in western China. The deployment of new instruments can therefore lead to substantial differences in the results obtained using the old instruments and their interpretation. Of these advances, we can highlight the improvement of reference methods, in which tightening the use of filter materials or changing the humidity at which filters are brought to equilibrium become important aspects for collecting particles on representative filters. Advanced PM2.5 instruments that use different approaches to deduce particle mass, size, number and shape are also being developed and deployed. The complexity of the atmospheric and chemical processes responsible for the formation of PM2.5 pollution in China requires the development of sound science to support a future emissions control strategy that can reduce this pollution. The results of several studies focusing on PM measurements and characterisation have

highlighted the importance of secondary aerosol contribution to the burden of PM2.5. For instance, nucleation and growth processes play a major factor in the secondary PM formation in Beijing[84]. The atmospheric reactions between the elevated concentrations of volatile organic compounds (VOCs), NOx and SOx emitted from anthropogenic sources were assumed to be responsible for the nucleation process. Nucleation, followed by the growth mode, has shown to be active in the Beijing area. Biogenic emission is also one of important contributor to the SOAs of PM2.5. To improve the understanding of PM2.5 formation in different Chinese airsheds, we need to deploy instruments that allow for accurate speciation of PM2.5 composition. Detailed knowledge about the speciation of VOC precursors would allow the development of chemical reaction pathways responsible for the formation of semi-volatile products, which drive the formation of aerosols. In addition, a better understanding of the nucleation, accumulation and agglomeration modes of aerosols in a controlled environment is needed to develop appropriate mechanisms describing these phenomena. All in all, an integrative approach, from collaboration among academia, government, and industries, can effectively improve monitoring accuracy to support managing and mitigating the PM2.5 pollution in China.

Acknowledgments This article was funded by the Special Fund for Environmental Protection Research in the Public Interest of China (Grant Number: 201309010) and the Scientific Research Foundation of the Higher Education Institutions of Hebei Province, China (Grant Number: QN2016024). The authors are grateful to Dr. Steve White from CSIRO who advised over the contents. Special thanks go to Ms. Kath Kovac from the CSIRO for help with polishing some sentences and Dr. Bin Han and Mr. Wen Yang from Chinese Research Academy of Environmental Sciences for providing some data.

References [1] E. Winijkul, F. Yan, Z. Lu, D.G. Streets, T.C. Bond, Y. Zhao, Size-resolved global emission inventory of primary particulate matter from energy-related combustion sources, Atmospheric Environment, 107 (2015) 137-147. [2] F. Yan, E. Winijkul, S. Jung, T.C. Bond, D.G. Streets, Global emission projections of particulate matter (PM): I. Exhaust emissions from on-road vehicles, Atmospheric Environment, 45 (2011) 4830-4844. [3] J. Han, B. Han, P. Li, S. Kong, Z. Bai, D. Han, X. Dou, X. Zhao, Chemical Characterizations of PM10 Profiles for Major Emission Sources in Xining, Northwestern China, Aerosol and Air Quality Research, 14 (2014) 1017-1027.

[4] G. Shi, X. Peng, J. Liu, Y. Tian, D. Song, H. Yu, Y. Feng, A.G. Russell, Quantification of long-term primary and secondary source contributions to carbonaceous aerosols, Environmental Pollution, 219 (2016) 897-905. [5] J.H. Seinfeld, Atmospheric chemistry and physics : from air pollution to climate change / John H. Seinfeld, Spyros N. Pandis, 2006. [6] F. Laden, J. Schwartz, F.E. Speizer, D.W. Dockery, Reduction in fine particulate air pollution and mortality - Extended follow-up of the Harvard six cities study, American Journal of Respiratory and Critical Care Medicine, 173 (2006) 667-672. [7] F. Dominici, R.D. Peng, M.L. Bell, L. Pham, A. McDermott, S.L. Zeger, J.M. Samet, Fine particulate air pollution and hospital admission for cardiovascular and respiratory diseases, Jama-Journal of the American Medical Association, 295 (2006) 1127-1134. [8] R.D. Brook, S. Rajagopalan, C.A. Pope, J.R. Brook, A. Bhatnagar, A.V. Diez-Roux, F. Holguin, Y.L. Hong, R.V. Luepker, M.A. Mittleman, A. Peters, D. Siscovick, S.C. Smith, L. Whitsel, J.D. Kaufman, E. Amer Heart Assoc Council, D. Council Kidney Cardiovasc, M. Council Nutr Phys Activity, Particulate Matter Air Pollution and Cardiovascular Disease An Update to the Scientific Statement From the American Heart Association, Circulation, 121 (2010) 2331-2378. [9] J. Schwartz, L.M. Neas, Fine particles are more strongly associated than coarse particles with acute respiratory health effects in schoolchildren, Epidemiology, 11 (2000) 6-10. [10] N. Englert, Fine particles and human health - a review of epidemiological studies, Toxicology Letters, 149 (2004) 235-242. [11] M. Kampa, E. Castanas, Human health effects of air pollution, Environmental Pollution, 151 (2008) 362-367. [12] M. Brauer, C. Lencar, L. Tamburic, M. Koehoorn, P. Demers, C. Karr, A cohort study of traffic-related air pollution impacts on birth outcomes, Environmental Health Perspectives, 116 (2008) 680-686. [13] W.J. Shaughnessy, M.M. Venigalla, D. Trump, Health effects of ambient levels of respirable particulate matter (PM) on healthy, young-adult population, Atmospheric Environment, 123, Part A (2015) 102-111. [14] S. Gupta, R. Agarwal, S.K. Mittal, Respiratory health concerns in children at some strategic locations from high PM levels during crop residue burning episodes, Atmospheric Environment, 137 (2016) 127-134. [15] S. Ohta, N. Murao, T. Moriya, Evaluation of absorption properties of atmospheric aerosols at solar wavelengths based on chemical characterization, Atmospheric Environment. Part A. General Topics, 24 (1990) 1409-1416. [16] N. Manago, S. Miyazawa, Bannu, H. Kuze, Seasonal variation of tropospheric aerosol properties by direct and scattered solar radiation spectroscopy, Journal of Quantitative Spectroscopy and Radiative Transfer, 112 (2011) 285-291. [17] T. Schumann, Aerosol and hydrometeor concentrations and their chemical composition during winter precipitation along a mountain slope — III. size-differentiated in-cloud scavenging efficiencies, Atmospheric Environment. Part A. General Topics, 25 (1991) 809-824.

[18] Y. Zhang, X.Y. Wen, C.J. Jang, Simulating chemistry–aerosol–cloud–radiation–climate feedbacks over the continental U.S. using the online-coupled Weather Research Forecasting Model with chemistry (WRF/Chem), Atmospheric Environment, 44 (2010) 3568-3582. [19] N.-H. Lin, A.M. Sayer, S.-H. Wang, A.M. Loftus, T.-C. Hsiao, G.-R. Sheu, N.C. Hsu, S.-C. Tsay, S. Chantara, Interactions between biomass-burning aerosols and clouds over Southeast Asia: Current status, challenges, and perspectives, Environmental Pollution, 195 (2014) 292-307. [20] J.F. Zhang, J.M. Samet, Chinese haze versus Western smog: lessons learned, Journal of Thoracic Disease, 7 (2015) 3-13. [21] B. Wang, Y. Zhao, Z. Lan, Y. Yao, L. Wang, H. Sun, Sampling methods of emerging organic contaminants in indoor air, Trends in Environmental Analytical Chemistry, 12 (2016) 13-22. [22] F. Drewnick, S.S. Hings, P. DeCarlo, J.T. Jayne, M. Gonin, K. Fuhrer, S. Weimer, J.L. Jimenez, K.L. Demerjian, S. Borrmann, D.R. Worsnop, A new time-of-flight aerosol mass spectrometer (TOF-AMS) - Instrument description and first field deployment, Aerosol Science and Technology, 39 (2005) 637-658. [23] C.A. Miller, R.K. Srivastava, C.B. Sedman, Advances in control Of PM2.5 and PM2.5 precursors generated by the combustion of pulverized coal, International Journal of Environment and Pollution, 17 (2002) 143-156. [24] W.G. Tucker, An overview of PM2.5 sources and control strategies, Fuel Processing Technology, 65 (2000) 379-392. [25] M.P. Walsh, PM2.5: global progress in controlling the motor vehicle contribution, Frontiers of Environmental Science & Engineering, 8 (2014) 1-17. [26] M. Yoshikawa, T. Uemura, D. Kan, T. Fukui, T. Charinpanitkul, W. Tanthapanichakoon, M. Naito, DEVELOPMENT OF FILTRATION TECHNOLOGY FOR PM2.5 IN DIESEL EXHAUST, in: K. Ewsuk, K. Nogi, R. Waesche, Y. Umakoshi, T. Hinklin, K. Uematsu, T. Tomsia, H. Abe, H. Kamiya, M. Naito (Eds.) Characterization and Control of Interfaces for High Quality Advanced Materials Ii2007, pp. 339-344. [27] Y.S. Zhang, C.Y. Wang, L. Wang, J.W. Cheng, K. Qiao, Control Technology of PM2.5 in Coal-Fired Power Plant and Experiment on dedusting performance of Typical filters to PM2.5, in: J. Zhao, R. Iranpour, X. Li, B. Jin (Eds.) Advances in Environmental Technologies, Pts 1-62013, pp. 2135-2139. [28] S.S. Amaral, J.A. de Carvalho, M.A.M. Costa, C. Pinheiro, An Overview of Particulate Matter Measurement Instruments, Atmosphere, 6 (2015) 1327-1345. [29] V. Tasić, M. Jovašević-Stojanović, S. Vardoulakis, N. Milošević, R. Kovačević, J. Petrović, Comparative assessment of a real-time particle monitor against the reference gravimetric method for PM10 and PM2.5 in indoor air, Atmospheric Environment, 54 (2012) 358-364. [30] R.A. Bilonick, D.P. Connell, E.O. Talbott, J.R. Rager, T. Xue, Using structural equation modeling to construct calibration equations relating PM2.5 mass concentration samplers to the federal reference method sampler, Atmospheric Environment, 103 (2015) 365-377. [31] M.o.E.P.o. China, Report on the State of the Environment in China, Beijing.

[32] A. van Donkelaar, R.V. Martin, M. Brauer, R. Kahn, R. Levy, C. Verduzco, P.J. Villeneuve, Global Estimates of Ambient Fine Particulate Matter Concentrations from Satellite-Based Aerosol Optical Depth: Development and Application, Environmental Health Perspectives, 118 (2010) 847-855. [33] R.J. Huang, Y.L. Zhang, C. Bozzetti, K.F. Ho, J.J. Cao, Y.M. Han, K.R. Daellenbach, J.G. Slowik, S.M. Platt, F. Canonaco, P. Zotter, R. Wolf, S.M. Pieber, E.A. Bruns, M. Crippa, G. Ciarelli, A. Piazzalunga, M. Schwikowski, G. Abbaszade, J. Schnelle-Kreis, R. Zimmermann, Z.S. An, S. Szidat, U. Baltensperger, I. El Haddad, A.S.H. Prevot, High secondary aerosol contribution to particulate pollution during haze events in China, Nature, 514 (2014) 218-222. [34] W.W. Buchberger, Detection techniques in ion chromatography of inorganic ions, TrAC Trends in Analytical Chemistry, 20 (2001) 296-303. [35] P.N. Nesterenko, Simultaneous separation and detection of anions and cations in ion chromatography, TrAC Trends in Analytical Chemistry, 20 (2001) 311-319. [36] P. Quincey, D. Butterfield, D. Green, M. Coyle, J.N. Cape, An evaluation of measurement methods for organic, elemental and black carbon in ambient air monitoring sites, Atmospheric Environment, 43 (2009) 5085-5091. [37] E.F. Mikhailov, S.Y. Mironova, M.V. Makarova, S.S. Vlasenko, T.I. Ryshkevich, A.V. Panov, M.O. Andreae, Studying seasonal variations in carbonaceous aerosol particles in the atmosphere over central Siberia, Izvestiya Atmospheric and Oceanic Physics, 51 (2015) 423-430. [38] M.A. Iqbal, K.-H. Kim, Sampling, pretreatment, and analysis of particulate matter and trace metals emitted through charcoal combustion in cooking activities, Trac-Trends in Analytical Chemistry, 76 (2016) 52-59. [39] S. Taner, B. Pekey, H. Pekey, Fine particulate matter in the indoor air of barbeque restaurants: Elemental compositions, sources and health risks, Science of The Total Environment, 454 (2013) 79-87. [40] R.J.C. Brown, M.J.T. Milton, Analytical techniques for trace element analysis: an overview, Trac-Trends in Analytical Chemistry, 24 (2005) 266-274. [41] M. Elbayoumi, N.A. Ramli, N.F.F.M. Yusof, Spatial and temporal variations in particulate matter concentrations in twelve schools environment in urban and overpopulated camps landscape, Building and Environment, 90 (2015) 157-167. [42] U. Dayan, I. Levy, The influence of meteorological conditions and atmospheric circulation types on PM10 and visibility in Tel Aviv, Journal of Applied Meteorology, 44 (2005) 606-619. [43] C. Rossi, P. Poli, A. Buschini, F. Cassoni, S. Cattani, E. DeMunari, Comparative investigations among meteorological conditions, air chemical-physical pollutants and airborne particulate mutagenicity: a long-term study (1990-1994) from a northern Italian town, Chemosphere, 30 (1995) 1829-1845. [44] D.Y.H. Pui, S.C. Chen, Z.L. Zuo, PM2.5 in China: Measurements, sources, visibility and health effects, and mitigation, Particuology, 13 (2014) 1-26. [45] J.L. Hu, Y.G. Wang, Q. Ying, H.L. Zhang, Spatial and temporal variability of PM2.5 and PM10 over the North China Plain and the Yangtze River Delta, China, Atmospheric Environment, 95 (2014) 598-609.

[46] P. Huang, J.Y. Zhang, Y.X. Tang, L. Liu, Spatial and Temporal Distribution of PM2.5 Pollution in Xi'an City, China, International Journal of Environmental Research and Public Health, 12 (2015) 6608-6625. [47] W. Huang, E.S. Long, J. Wang, R.Y. Huang, L. Ma, Characterizing spatial distribution and temporal variation of PM10 and PM2.5 mass concentrations in an urban area of Southwest China, Atmospheric Pollution Research, 6 (2015) 842-848. [48] M.F. Zhao, Z.S. Huang, T. Qiao, Y.K. Zhang, G.L. Xiu, J.Z. Yu, Chemical characterization, the transport pathways and potential sources of PM2.5 in Shanghai: Seasonal variations, Atmospheric Research, 158 (2015) 66-78. [49] S.C. Lai, Y. Zhao, A.J. Ding, Y.Y. Zhang, T.L. Song, J.Y. Zheng, K.F. Ho, S.C. Lee, L.J. Zhong, Characterization of PM2.5 and the major chemical components during a 1-year campaign in rural Guangzhou, Southern China, Atmospheric Research, 167 (2016) 208-215. [50] J. Gao, X. Peng, G. Chen, J. Xu, G.L. Shi, Y.C. Zhang, Y.C. Feng, Insights into the chemical characterization and sources of PM2.5 in Beijing at a 1-h time resolution, Science of The Total Environment, 542 (2016) 162-171. [51] J.H. Tan, J.C. Duan, Y.L. Ma, K.B. He, Y. Cheng, S.X. Deng, Y.L. Huang, S.P. Si-Tu, Long-term trends of chemical characteristics and sources of fine particle in Foshan City, Pearl River Delta: 2008-2014, Science of The Total Environment, 565 (2016) 519-528. [52] N.N. Maykut, J. Lewtas, E. Kim, T.V. Larson, Source apportionment of PM2.5 at an urban IMPROVE site in Seattle, Washington, Environmental Science & Technology, 37 (2003) 5135-5142. [53] J.-K. Choi, S.-J. Ban, Y.-P. Kim, Y.-H. Kim, S.-M. Yi, K.-D. Zoh, Molecular marker characterization and source appointment of particulate matter and its organic aerosols, Chemosphere, 134 (2015) 482-491. [54] C.-S. Liang, F.-K. Duan, K.-B. He, Y.-L. Ma, Review on recent progress in observations, source identifications and countermeasures of PM2.5, Environment International, 86 (2016) 150-170. [55] W.Y. Xu, C.S. Zhao, L. Ran, Z.Z. Deng, N. Ma, P.F. Liu, W.L. Lin, P. Yan, X.B. Xu, A new approach to estimate pollutant emissions based on trajectory modeling and its application in the North China Plain, Atmospheric Environment, 71 (2013) 75-83. [56] S. Lee, W. Liu, Y. Wang, A.G. Russell, E.S. Edgerton, Source apportionment of PM2.5: Comparing PMF and CMB results for four ambient monitoring sites in the southeastern United States, Atmospheric Environment, 42 (2008) 4126-4137. [57] M. Zheng, G.R. Cass, J.J. Schauer, E.S. Edgerton, Source apportionment of PM2.5 in the southeastern United States using solvent-extractable organic compounds as tracers, Environmental Science & Technology, 36 (2002) 2361-2371. [58] A.M. Taiwo, Source Apportionment of Urban Background Particulate Matter in Birmingham, United Kingdom Using a Mass Closure Model, Aerosol and Air Quality Research, 16 (2016) 1244-1252. [59] A.M. Taiwo, R.M. Harrison, D.C.S. Beddows, Z. Shi, Source apportionment of single particles sampled at the industrially polluted town of Port Talbot, United Kingdom by ATOFMS, Atmospheric Environment, 97 (2014) 155-165.

[60] L.X. Yang, S.H. Cheng, X.F. Wang, W. Nie, P.J. Xu, X.M. Gao, C. Yuan, W.X. Wang, Source identification and health impact of PM2.5 in a heavily polluted urban atmosphere in China, Atmospheric Environment, 75 (2013) 265-269. [61] N.B. Geng, J. Wang, Y.F. Xu, W.D. Zhang, C. Chen, R.Q. Zhang, PM2.5 in an industrial district of Zhengzhou, China: Chemical composition and source apportionment, Particuology, 11 (2013) 99-109. [62] J. Tao, J. Gao, L. Zhang, R. Zhang, H. Che, Z. Zhang, Z. Lin, J. Jing, J. Cao, S.C. Hsu, PM2.5 pollution in a megacity of southwest China: source apportionment and implication, Atmospheric Chemistry and Physics, 14 (2014) 8679-8699. [63] L. Yao, L.X. Yang, Q. Yuan, C. Yan, C. Dong, C.P. Meng, X. Sui, F. Yang, Y.L. Lu, W.X. Wang, Sources apportionment of PM2.5 in a background site in the North China Plain, Science of The Total Environment, 541 (2016) 590-598. [64] X.H. Qiu, L. Duan, J. Gao, S.L. Wang, F.H. Chai, J. Hu, J.Q. Zhang, Y.R. Yun, Chemical composition and source apportionment of PM10 and PM2.5 in different functional areas of Lanzhou, China, Journal of Environmental Sciences, 40 (2016) 75-83. [65] Y.Z. Tian, G. Chen, H.T. Wang, Y.Q. Huang-Fu, G.L. Shi, B. Han, Y.C. Feng, Source regional contributions to PM2.5 in a megacity in China using an advanced source regional apportionment method, Chemosphere, 147 (2016) 256-263. [66] J. Wang, Y.F. Zhang, Y.C. Feng, X.J. Zheng, L. Jiao, S.M. Hong, J.D. Shen, T. Zhu, J. Ding, Q. Zhang, Characterization and source apportionment of aerosol light extinction with a coupled model of CMB-IMPROVE in Hangzhou, Yangtze River Delta of China, Atmospheric Research, 178 (2016) 570-579. [67] B.S. Liu, N. Song, Q.L. Dai, R.B. Mei, B.H. Sui, X.H. Bi, Y.C. Feng, Chemical composition and source apportionment of ambient PM2.5 during the non-heating period in Taian, China, Atmospheric Research, 170 (2016) 23-33. [68] X.F. Huang, H. Yun, Z.H. Gong, X. Li, L. He, Y.H. Zhang, M. Hu, Source apportionment and secondary organic aerosol estimation of PM2.5 in an urban atmosphere in China, Science China-Earth Sciences, 57 (2014) 1352-1362. [69] T. Qiao, M.F. Zhao, G.L. Xiu, J.Z. Yu, Simultaneous monitoring and compositions analysis of PM1 and PM2.5 in Shanghai: Implications for characterization of haze pollution and source apportionment, Science of The Total Environment, 557 (2016) 386-394. [70] M.o.E.P.o.t.P.s.R.o. China, http://kjs.mep.gov.cn/hjbhbz/bzwb/dqhjbh/dqhjzlbz/201203/W0201204103302323 98521.pdf. [71] EPA, https://www.epa.gov/criteria-air-pollutants/naaqs-table. [72] E. commission, http://ec.europa.eu/environment/air/quality/standards.htm. [73] W.H. Organization, http://www.who.int/mediacentre/factsheets/fs313/en/. [74] S. Du, Z. Bai, L. Hou, PM2.5 monitoring method and application Science Press, Beijing, 2016. [75] P.C. Raynor, D. Leith, K.W. Lee, R. Mukund, Sampling and Analysis Using Filters, Aerosol Measurement, John Wiley & Sons, Inc.2011, pp. 107-128.

[76] Z.Y. Zhang, X.L. Zhang, D.Y. Gong, W.J. Quan, X.J. Zhao, Z.Q. Ma, S.J. Kim, Evolution of surface O-3 and PM2.5 concentrations and their relationships with meteorological conditions over the last decade in Beijing, Atmospheric Environment, 108 (2015) 67-75. [77] J.C. Chow, Measurement Methods to Determine Compliance with Ambient Air Quality Standards for Suspended Particles, Journal of the Air & Waste Management Association, 45 (1995) 320-382. [78] Y.L. Wang, W. Yang, B. Han, W.J. Zhang, M.D. Chen, Z.P. Bai, Gravimetric analysis for PM2.5 mass concentration based on year-round monitoring at an urban site in Beijing, Journal of Environmental Sciences, 40 (2016) 154-160. [79] A. Chung, D.P.Y. Chang, M.J. Kleeman, K.D. Perry, T.A. Cahill, D. Dutcher, E.M. McDougall, K. Stroud, Comparison of real-time instruments used to monitor airborne particulate matter, Journal of the Air & Waste Management Association, 51 (2001) 109-120. [80] J. Sciare, H. Cachier, R. Sarda-Esteve, T. Yu, X. Wang, Semi-volatile aerosols in Beijing (RP China): Characterization and influence on various PM2.5 measurements, Journal of Geophysical Research-Atmospheres, 112 (2007). [81] C. Yan, Z. Yihua, S. Fei, S. Liping, H. Haiyan, Determination of PM2.5 concentration by manual sampling and auto monitoring, ENVIRONMENTAL SCIENCE AND MANAGEMENT, (2012) 110-113. [82] J. LI, L. DU, X. WANG, B. PAN, L. LI, G. LI, H. ZHENG, W. WANG, Y. ZHAO, S. XIE, B. LIU, W. WANG, The test report in the first phaseand technical requirements of PM2.5 automatic monitoring instruments, China national environmental monitoring centre, Beijing, 2012. [83] J.E. Thompson, Crowd-sourced air quality studies: A review of the literature & portable sensors, Trends in Environmental Analytical Chemistry, 11 (2016) 23-34. [84] S. Guo, M. Hu, M.L. Zamora, J. Peng, D. Shang, J. Zheng, Z. Du, Z. Wu, M. Shao, L. Zeng, M.J. Molina, R. Zhang, Elucidating severe urban haze formation in China, Proceedings of the National Academy of Sciences of the United States of America, 111 (2014) 17373-17378.

Fig. 1 PM2.5 annual average concentration in China’s main regions and cities[31]

Fig. 2 PM2.5 speciation indifferent cities of China

Fig.3 The major sources of PM2.5 in selected Chinese cities

Table 1 Techniques used to characterise the chemical composition of PM2.5 Components

Sources/formation

Analytical methods

Sulfate, nitrate, ammonium

All sources contributing to SOx and NOx emissions, such as power generation, motor vehicles, energy-intensive industry, agriculture activities

Ion chromatography [34, 35]

Elemental carbon

Formed during combustion of fossil fuels

Thermo-optical method corrected for charring [36, 37]

Organic carbon

Originates partly directly from combustion sources, and as a secondary pollutant formed by oxidation of volatile organic compounds

Thermo-optical method corrected for charring [36, 37]

Trace metals, including lead, cadmium, mercury, nickel, chromium, zinc, manganese

Generated mainly by metallurgical processes, such as steelmaking, or from fuel additives

Inductively coupled plasma mass spectrometry (ICP-MS) or graphite furnace atomic absorption spectroscopy or inductively-coupled plasma atomic emission spectroscopy (ICP-AES) [38-40]

Minerals: aluminium, silicon, iron, calcium

Crustal materials (rock and soil) arising from construction, quarrying and wind-driven dust

ICP-MS or ICP-AES [38-40]

Trace organic compounds

Very large number of individual organic compounds. arising directly from fuel combustion processes and generated by traffic and solvents

ICP-MS or ICP-AES [38-40]

Sodium chloride

Sea salt

Ion chromatography [34, 35]

Table 2 PM2.5 standards set by different countries and organisations China [70] PM2.5 (μm/m3)

24-h average Annual average

United States Environmental

European Union [72]

World Health Organization [73]

Grade I

Grade II

Protection Agency [71]

35

75

35

–

25

15

35

12 (primary)

25

10

15(secondary)

Note: Grade I standards apply to category I of ambient air quality function regions, such as nature reserves, scenic areas and other areas that need to be protected. Grade II standards apply to category II of ambient air quality function regions, such as residential areas, combination areas with commercial, transportation and residential areas, cultural areas, industrial areas and rural areas.

Table 3 The standards and specifications of ambient air particle measurement in China [74] Standard code

Standard name

HJ 618-2011

Determination of atmospheric particles PM10 and PM2.5 in ambient air by gravimetric method

HJ 93-2013

Specifications and test procedures for PM10 and PM2.5 sampler

HJ 653-2013

Specifications and test procedures for ambient-air-quality continuous automated monitoring system for PM10 and PM2.5

HJ 655-2013

Technical specifications for installation and acceptance of ambient-air-quality continuous automated monitoring system for PM10 and PM2.5

HJ 656-2013

Technical specifications for gravimetric-measurement methods for PM2.5 in ambient air

HJ 664-2013

Technical regulation for selection of ambient-air-quality monitoring stations (on trial)

Table 4 Advantages and limitations of various PM2.5sampling filters [75] Filter types Glass fibre

Quartz

Teflon/Polytetrafluoroethylene

Advantages 

Low pressure drop during high-volume sampling

 

Low cost High particulate-loading capacity



Stable to temperatures up to 800 C

 

Friable Humidity effect



Low trace contaminant levels





Can be baked to remove trace organics before sampling

Artifact nitrate formation has been



Particle collection occurs throughout the depth of the filter

observed



Low artifact formation



Inert to chemical transformations



Loss of nitrates observed



Extremely low moisture sensitivity



Temperature range limited to about



Low race/background concentrations

150 C for supported membranes and



Chemical resistant

260 C for pure PTFE membranes

 

Low moisture uptake Minimises chemical transformation artifacts

(PTFE)

PTFE-coated glass fibre

Limitations



Artifact nitrate

Table 5 Summary of regression analysis of online measurement by different instruments against the gravimetric method for PM2.5 in Jinan, China Parameter

Performance

A

B

C

D

E

F

1±0.15

0.75

1.14

1.03

0.97

0.88

0.96

Intercept (μg/m3)

≤±10

–25

–40

–25

–23

4.1

–8.6

Correlation coefficient (r)

≥0.93

0.951

0.952

0.952

0.942

0.945

0.956

Sample number>23 days

N/A

36

32

36

35

28

36

Slope (dimensionless)

requirements

Notes: A–E are overseas instruments, F is a domestic instrument.