key: cord-0739064-y5zm7z3y authors: Ma, Qingxin; Qi, Yu; Shan, Qiuli; Liu, Sijin; He, Hong title: Understanding the knowledge gaps between air pollution controls and health impacts including pathogen epidemic date: 2020-07-19 journal: Environ Res DOI: 10.1016/j.envres.2020.109949 sha: ee8ea1993a9e607e9a0389d1fb0fd96637669192 doc_id: 739064 cord_uid: y5zm7z3y Sustainable development calls for a blue sky with quality air. Encouragingly, the current mass reduction-oriented pollution control is making substantial achievements, as the data from Chinese Environmental Monitoring Stations show a significant drop in the annual average concentrations of particulate matters (i.e., PM(10) and PM(2.5)) and SO(2). But many challenges and knowledge gaps are still confronted nowadays. On one hand, long-term health impacts of fine air particles have to be closely probed through both epidemiological and laboratory studies, and the toxic effects owing to the interactions between particles and associated chemical pollutants should be differentially teased out. On the other hand, due to sole mass control, there are significant changes of overall pollutant fingerprint, such as the increase of ground-level ozone concentration, which should be taken into account for altered health effects relative to the past. Moreover, the interplays with air pollutants and air-borne pathogens should be scrutinized in more details. In other words, it is worth investigating likely spread of pathogens (even for SARS-CoV-2) with aid of aerosols. Here, we recapitulate the current knowledge gaps between air pollution controls and health impacts including pathogen epidemic, and we also propose future research directions to support policy making in balance mass control and health impacts. Air pollution poses an outstanding challenge to sustainable development, human health and even pathogen epidemics. According to the report of World Health Organization (WHO) in 2019, air pollution ranked in the first place of top 10 threats to human health. 1 Under this setting, air pollution control and according health risks have popularly emerged in both academic research and strategic agendas worldwide. Although significant achievements have been reached due to the efforts in improving air quality in recent decades, there still exist many hurdles with respect to health issues to be addressed, e.g., geographical differences in pathophysiological responses to air pollution, insufficient long-term epidemiological data, uncertainty on the divergent toxicities due to the complicated interactions among versatile environmental factors from different sources, and previously neglected or underestimated adverse effects. Moreover, as the mass of particulate particles (such as fine particulate matter, PM 2.5 ) falls, the ground-level O 3 concentration arises (Figure 1 ), 2 which may cause unknown threats to humans. Importantly, mounting data evidence the implications of air pollution in pathogen spread and epidemics. 3 Air pollution has been recently found to correlate to increased risk of active tuberculosis 4 and influenza 5 . Strikingly, the current outbreak of novel coronavirus pneumonia (COVID-19) caused by the 2019 novel coronavirus (SARS-CoV-2) is attracting global attention. However, there is still no insight into the reasons for its outbreak from the eco-environmental and climate aspects. It would be great interest to embark on the role of aerosols, especially in indoor circumstance and airtight space, in enhancing the transport, viability and infection of the SARS-CoV-2 virus. [6] [7] Thus, the sole mass decline of total air pollutants may not be able to reflect the full profiles of health impacts (Figure 2 ). To this end, here we summarize the current knowledge gaps Page 5 of 21 between air pollution controls and health impacts, and discuss the future development in health impact assessment upon air pollution. In recent decades, China has been suffering serious air pollution, especially the high loading PM 2.5 . Challenged by diverse serious problems caused by air pollution, the Chinese government has largely increased investment in basic research on air pollution formation and control. These studies greatly expand the understanding of the formation mechanism and fundamental principles of air pollution. It is now recognized that air pollution in China is a new type of haze chemical smog, different from London smog and Los Angeles photochemical smog. 8 The complexity of air pollution resides in its versatile sources, including coal combustion emissions, vehicle emissions, agricultural emissions, industrial emissions and high concentration of natural dust aerosol. 9 In the meanwhile, the numerical model for early warning and forecast of air pollution has been greatly upgraded, and the prediction accuracy has also been significantly improved, providing an important scientific support for taking effective pollution control measures and the health assessment of air pollution. On the basis of these scientific understandings, Chinese government has strengthened the furious regulations on the control of these critical source emission in recent decades. 10 In fact, over a long-term timescale, the reduction of Frankly speaking, the situation of PM pollution varies from place to place and from time to time in China, in that numerous industrialized cities undergo heavier pollution than western countries, giving rise to greater challenges in pollution control and health impact evaluation. Nonetheless, recent epidemiological studies indicate that PM pollution would increase the occurrence of incident stroke, ischemic heart diseases and even impaired fetal growth. [12] [13] Moreover, many in vitro models have been developed for the regarding toxic effects of pollutants that are adhered on PMs has also been a highly active topic. The high-risk components in PMs exhibit significant temporal-spatial variation. [17] [18] Therefore, it has been argued that the infrastructure of PMs and laden pollutants (e.g., polycyclic aromatic hydrocarbons (PAHs) and heavy metals) on PMs together account for the overall net toxicity (Figure 2 ). PAHs and toxic heavy metals are often integrated into PMs through anthropogenic atmospheric emissions. Studies actually suggest that PAHs and heavy metals on PMs are deemed to be the determining causes of a range of diseases, ranging from asthma, emphysema to lung cancers. [19] [20] However, the bio-availability of such pollutants once integrated on PMs, namely their release from particles in biological Page 8 of 21 system, as well as their individual toxic effects, still remain elusive (Figure 2 ). In addition, due to complex interplay of chemicals and unknown surface properties on PMs, the desorption mechanism of chemicals from PMs in biological settings and likely "Trojan Horse" (i.e. vehicle-conduced delivery) effects are intertwined and could not be readily differentiated. 21 Third, little is known about the potential bio-transformation of PMs in biological systems. Due to the large surface area and ample active functional groups, PMs would react with bio-molecules (e.g., surfactants, enzymes and lipids), [22] [23] and PMs may catalyze the formation of reactive oxygen species (ROS) undermined cellular oxidative potential, leading to oxidative stress and even cell death. [24] [25] This process might also induce bio-transformation of PMs, which may alter their physicochemical properties, such as aggregation state, enzyme-mediated changes of functional groups and even degradation by biomolecules ( Figure 2) . 22, [26] [27] The bio-transformation would consequently alter the bio-reactivity and bio-safety profiles of particles. 23 Thus far, future work should aim to interrogate the toxicity mechanisms underlying PMs per se and their transformation under biological conditions. Importantly, another previously underestimated issue is the transmission of pathogens through PMs and aerosols in the atmosphere as well as the indoor environments ( Figure 2 ). So far, only a few studies have looked into the interplay between pathogens (i.e., viruses and bacteria) and air pollution. 5, [28] [29] Although most reports documented that influenza virus dissemination relies on short-distance dispersion of droplets from cough or sneeze, mainly through indoor aerosols, a crucial role of PMs in facilitating virus transport in longer distance has been also proposed. [30] [31] Moreover, mounting evidence suggests that air pollutants, e.g., SO 2 and PMs, positively correlated Together, the mass reduction oriented-control policy is desirable when the air pollution was serious in the past years. With the great decline in the total mass of air pollutants, more efforts should be devoted to accurate prediction of air pollution, precision control of specific components, and adequate insights into health effects under chronic exposure and upon altered pollutant profiles. Under this setting, many obstacles should be addressed in the future, such as the health risks of PMs and adherent pollutants, the interplays between the spread of air-borne pathogens and air pollution, and the synergistic health effects of O 3 and other air pollutants. Hence, the focuses on health risks of air pollution should involve diverse fields, such as molecular biology, toxicology and environmental chemistry, epidemiology and even clinical medicine. The laboratory experimental systems also need to be improved to reach realistic atmosphere standards. Moreover, a more openly shared database for air conditions, toxicological results and epidemic data could be commonly shared and integrated worldwide. Thereby, filling in these fundamental knowledges would be surely beneficial in gaining new insights into health risks, a prerequisite of for policy-making of precision control of air pollution. 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(Data collected from Chinese Bulletin on Environmental Conditions Page 12 of 21 The authors declare no competing financial interest.Page 13 of 21 The authors declare no competing financial interest.