Showing papers by "Tuukka Petäjä published in 2021"

Is reducing new particle formation a plausible solution to mitigate particulate air pollution in Beijing and other Chinese megacities

Abstract: Atmospheric gas-to-particle conversion is a crucial or even dominant contributor to haze formation in Chinese megacities in terms of aerosol number, surface area and mass. Based on our comprehensive observations in Beijing during 15 January 2018-31 March 2019, we are able to show that 80-90% of the aerosol mass (PM2.5) was formed via atmospheric reactions during the haze days and over 65% of the number concentration of haze particles resulted from new particle formation (NPF). Furthermore, the haze formation was faster when the subsequent growth of newly formed particles was enhanced. Our findings suggest that in practice almost all present-day haze episodes originate from NPF, mainly since the direct emission of primary particles in Beijing has considerably decreased during recent years. We also show that reducing the subsequent growth rate of freshly formed particles by a factor of 3-5 would delay the buildup of haze episodes by 1-3 days. Actually, this delay would decrease the length of each haze episode, so that the number of annual haze days could be approximately halved. Such improvement in air quality can be achieved with targeted reduction of gas-phase precursors for NPF, mainly dimethyl amine and ammonia, and further reductions of SO2 emissions. Furthermore, reduction of anthropogenic organic and inorganic precursor emissions would slow down the growth rate of newly-formed particles and consequently reduce the haze formation.

The Synergistic Role of Sulfuric Acid, Bases, and Oxidized Organics Governing New-Particle Formation in Beijing

Abstract: Intense and frequent new particle formation (NPF) events have been observed in polluted urban environments, yet the dominant mechanisms are still under debate. To understand the key species and governing processes of NPF in polluted urban environments, we conducted comprehensive measurements in downtown Beijing during January–March, 2018. We performed detailed analyses on sulfuric acid cluster composition and budget, as well as the chemical and physical properties of oxidized organic molecules (OOMs). Our results demonstrate that the fast clustering of sulfuric acid (H2SO4) and base molecules triggered the NPF events, and OOMs further helped grow the newly formed particles toward climateand health-relevant sizes. This synergistic role of H2SO4, base species, and OOMs in NPF is likely representative of polluted urban environments where abundant H2SO4 and base species usually co-exist, and OOMs are with moderately low volatility when produced under high NOx concentrations. Plain Language Summary Atmospheric new particle formation (NPF) is a dominant source of atmospheric ultrafine particles worldwide. Those particles profoundly influence climate and human health. NPF includes two consecutive processes, that is, the formation of new particles (∼2 nm in diameter) and their subsequent growth to larger sizes. Extensive studies conducted in the laboratory and in forested areas have shown that many gaseous species can participate in NPF, such as sulfuric acid, ammonia, amines, and oxidize organic molecules. However, the actual roles of these vapors may vary significantly from location to location and are largely unclear in urban environments. Here, based on measurements of sulfuric acid, sulfuric acid clusters, and oxidize organic molecules, we demonstrate that sulfuric acid and base molecules were responsible for the initial formation of new particles during a wintertime field campaign in Beijing. The majority of oxidized organic molecules had a minor YAN ET AL. © 2021. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. The Synergistic Role of Sulfuric Acid, Bases, and Oxidized Organics Governing New-Particle Formation in Beijing Chao Yan , Rujing Yin, Yiqun Lu , Lubna Dada , Dongsen Yang, Yueyun Fu, Jenni Kontkanen , Chenjuan Deng, Olga Garmash , Jiaxin Ruan, Rima Baalbaki , Meredith Schervish, Runlong Cai, Matthew Bloss, Tommy Chan , Tianzeng Chen , Qi Chen, Xuemeng Chen, Yan Chen, Biwu Chu, Kaspar Dällenbach, Benjamin Foreback, Xucheng He, Liine Heikkinen , Tuija Jokinen, Heikki Junninen, Juha Kangasluoma , Tom Kokkonen , Mona Kurppa, Katrianne Lehtipalo , Haiyan Li, Hui Li , Xiaoxiao Li, Yiliang Liu, Qingxin Ma , Pauli Paasonen , Pekka Rantala , Rosaria E. Pileci , Anton Rusanen, Nina Sarnela , Pauli Simonen , Shixian Wang, Weigang Wang , Yonghong Wang , Mo Xue, Gan Yang, Lei Yao, Ying Zhou, Joni Kujansuu, Tuukka Petäjä, Wei Nie , Yan Ma, Maofa Ge , Hong He, Neil M. Donahue , Douglas R. Worsnop, Veli-Matti Kerminen, Lin Wang , Yongchun Liu, Jun Zheng , Markku Kulmala , Jingkun Jiang , and Federico Bianchi Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Aerosol and Haze Laboratory, Beijing University of Chemical Technology, Beijing, China, Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Helsinki, Finland, School of Environment, State Key Joint Laboratory of Environment Simulation and Pollution Control, Tsinghua University, Beijing, China, Department of Environmental Science & Engineering, Fudan University, Shanghai, China, Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Nanjing University of Information Science & Technology, Nanjing, China, Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA, USA, Research Center for EcoEnvironmental Sciences, Chinese Academy of Science, Beijing, China, School of Environmental Sciences, Peking University, Beijing, China, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China, Laboratory of Environmental Physics, Institute of Physics, University of Tartu, Tartu, Estonia, Finnish Meteorological Institute, Helsinki, Finland, Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), Villigen, Switzerland, Aerosol Physics Laboratory, Physics Unit, Tampere University, Tampere, Finland, School of Atmospheric Sciences, Joint International Research Laboratory of Atmospheric and Earth System Sciences, Nanjing University, Nanjing, China, Aerodyne Research Inc., Billerica, MA, USA Key Points: • Process-level understanding of new particle formation (NPF) in wintertime Beijing was obtained based on measurement state-of-theart instruments • The analysis of sulfuric acid cluster composition and budget showed that sulfuric acid-base clustering initiated NPF • Condensable organic vapors were characterized and demonstrated to have a crucial influence on the growth of newly formed particles Supporting Information: Supporting Information may be found in the online version of this article.

The seasonal cycle of ice-nucleating particles linked to the abundance of biogenic aerosol in boreal forests

Abstract: . Ice-nucleating particles (INPs) trigger the formation of cloud ice crystals in the atmosphere. Therefore, they strongly influence cloud microphysical and optical properties, as well as precipitation and the life cycle of clouds. Improving weather forecasting and climate projection requires an appropriate formulation of atmospheric INP concentrations. This remains challenging, as the global INP distribution and variability depend on a variety of aerosol types and sources, and neither their short-term variability nor their long-term seasonal cycles are well covered by continuous measurements. Here, we provide the first year-long set of observations with a pronounced INP seasonal cycle in a boreal forest environment. Besides the observed seasonal cycle in INP concentrations with a minimum in wintertime and maxima in early and late summer, we also provide indications for a seasonal variation in the prevalent INP type. We show that the seasonal dependency of INP concentrations and prevalent INP types is most likely driven by the abundance of biogenic aerosol. As current parameterizations do not reproduce this variability, we suggest a new parameterization approach, which considers the seasonal variation of INP concentrations. For this, we use the ambient air temperature as a proxy for the season which affects the source strength of biogenic emissions and by that the INP abundance over the boreal forest areas. Furthermore, we provide new INP parameterizations based on the Ice Nucleation Active Surface Site (INAS) approach, which specifically describes the ice nucleation activity of boreal aerosols particles prevalent in different seasons. Our results characterize the boreal forest as an important but variable INP source and provide new perspectives to describe these new findings in atmospheric models.

Biogenic particles formed in the Himalaya as an important source of free tropospheric aerosols

Abstract: Aerosols of biogenic and anthropogenic origin affect the total radiative forcing of global climate. Poor knowledge of the pre-industrial aerosol concentration and composition, in particular of particles formed directly in the atmosphere from gaseous precursors, constitutes a large uncertainty in the anthropogenic radiative forcing. Investigations of new particle formation at pre-industrial-like conditions can contribute to the reduction of this uncertainty. Here we present observations taken at the remote Nepal Climate Observatory Pyramid station at 5,079 m above sea level, a few kilometres from the summit of Everest. We show that up-valley winds funnel gaseous aerosol precursors to higher altitudes. During this transport, these are oxidized into compounds of very low volatility, which rapidly form a large number of aerosol particles. These are then transported into the free troposphere, which suggests that the whole Himalayan region may act as an ‘aerosol factory’ and contribute substantially to the free tropospheric aerosol population. Aerosol production in this region occurs mainly via organic precursors of biogenic origin with little evidence of the involvement of anthropogenic pollutants. This process is therefore likely to be essentially unchanged since the pre-industrial period, and may have been one of the major sources that contributes to the upper tropospheric aerosol population during that time. Newly formed biogenic particles in the Himalaya increase free-tropospheric background aerosol concentration by a factor of up to two.

Seasonality of the particle number concentration and size distribution: a global analysis retrieved from the network of Global Atmosphere Watch (GAW) near-surface observatories

Abstract: . Aerosol particles are a complex component of the atmospheric system which influence climate directly by interacting with solar radiation, and indirectly by contributing to cloud formation. The variety of their sources, as well as the multiple transformations they may undergo during their transport (including wet and dry deposition), result in significant spatial and temporal variability of their properties. Documenting this variability is essential to provide a proper representation of aerosols and cloud condensation nuclei (CCN) in climate models. Using measurements conducted in 2016 or 2017 at 62 ground-based stations around the world, this study provides the most up-to-date picture of the spatial distribution of particle number concentration ( Ntot ) and number size distribution (PNSD, from 39 sites). A sensitivity study was first performed to assess the impact of data availability on Ntot 's annual and seasonal statistics, as well as on the analysis of its diel cycle. Thresholds of 50 % and 60 % were set at the seasonal and annual scale, respectively, for the study of the corresponding statistics, and a slightly higher coverage (75 %) was required to document the diel cycle. Although some observations are common to a majority of sites, the variety of environments characterizing these stations made it possible to highlight contrasting findings, which, among other factors, seem to be significantly related to the level of anthropogenic influence. The concentrations measured at polar sites are the lowest ( ∼ 10 2 cm −3 ) and show a clear seasonality, which is also visible in the shape of the PNSD, while diel cycles are in general less evident, due notably to the absence of a regular day–night cycle in some seasons. In contrast, the concentrations characteristic of urban environments are the highest ( ∼ 10 3 –10 4 cm −3 ) and do not show pronounced seasonal variations, whereas diel cycles tend to be very regular over the year at these stations. The remaining sites, including mountain and non-urban continental and coastal stations, do not exhibit as obvious common behaviour as polar and urban sites and display, on average, intermediate Ntot ( ∼ 10 2 –10 3 cm −3 ). Particle concentrations measured at mountain sites, however, are generally lower compared to nearby lowland sites, and tend to exhibit somewhat more pronounced seasonal variations as a likely result of the strong impact of the atmospheric boundary layer (ABL) influence in connection with the topography of the sites. ABL dynamics also likely contribute to the diel cycle of Ntot observed at these stations. Based on available PNSD measurements, CCN-sized particles (considered here as either >50 nm or >100 nm) can represent from a few percent to almost all of Ntot , corresponding to seasonal medians on the order of ∼ 10 to 1000 cm −3 , with seasonal patterns and a hierarchy of the site types broadly similar to those observed for Ntot . Overall, this work illustrates the importance of in situ measurements, in particular for the study of aerosol physical properties, and thus strongly supports the development of a broad global network of near surface observatories to increase and homogenize the spatial coverage of the measurements, and guarantee as well data availability and quality. The results of this study also provide a valuable, freely available and easy to use support for model comparison and validation, with the ultimate goal of contributing to improvement of the representation of aerosol–cloud interactions in models, and, therefore, of the evaluation of the impact of aerosol particles on climate.

Global air quality and covid-19 pandemic: Do we breathe cleaner air?

Abstract: The authors of this study truly appreciate the funding provided by Nazarbayev University through the Collaborative Research Grant (grant number: 091019CRP2104). MAT, MN, EA, and NE are the members of the Chemical and Aerosol Research Team (CART) and also the Environment and Resource Efficiency Cluster (EREC) at Nazarbayev University, and they would like to acknowledge the resources provided by CART and EREC to conduct this research. For India, except for Delhi, daily and hourly averaged air quality data were obtained from the Central Pollution Control Board (CPCB) CCR, OpenAQ or Air quality historical data platform, and location of stations were obtained from the OpenAQ website. CPCB is gratefully acknowledged for making the data available. Further, the CPCB data were consolidated and curated by Mr Prem Maheshwarkar, Earth and Environmental Sciences, IISER Bhopal whose contribution is also acknowledged. In Chile, the contributions made by Mr. Roberto Martinez, Head of the Planning and the Standards, Department of the Air Quality and Climate Change Division, Ministry for the Environment to provide data to this study, are greatly appreciated. In Brazil, CETESB (Environmental Company of the State of Sao Paulo) is acknowledged for its contribution to data preparation. In Cyprus, the authors would like to thank the Department of Labor Inspection of the Ministry of Environment of the Republic of Cyprus for providing the observational data for their monitoring network. For New Zealand, authors acknowledge the Environment Canterbury as the source for the Christchurch data. For Spain, Barcelona, the authors would like to thank "Department of Environmental Quality, Generalitat de Catalunya" as the data source. Turkish Ministry of Environment and Urbanization and Turkish State of Meteorological Services provided air quality and meteorological data, respectively, that are greatly appreciated. In the Netherlands, data were obtained from the National Institute for Public Health and the Environment (RIVM) and contained additional data from the GGD Amsterdam (provided by Dave de Jonge) and the DCMR Environmental Protection Agency (provided by Ed van der Gaag) and National Institute for Public Health and the Environment (RIVM) that are greatly appreciated. The authors would like to thank Tehran Air Quality Control Company for providing the data for the city of Tehran.

The driving factors of new particle formation and growth in the polluted boundary layer

Abstract: . New particle formation (NPF) is a significant source of atmospheric particles, affecting climate and air quality. Understanding the mechanisms involved in urban aerosols is important to develop effective mitigation strategies. However, NPF rates reported in the polluted boundary layer span more than 4 orders of magnitude, and the reasons behind this variability are the subject of intense scientific debate. Multiple atmospheric vapours have been postulated to participate in NPF, including sulfuric acid, ammonia, amines and organics, but their relative roles remain unclear. We investigated NPF in the CLOUD chamber using mixtures of anthropogenic vapours that simulate polluted boundary layer conditions. We demonstrate that NPF in polluted environments is largely driven by the formation of sulfuric acid–base clusters, stabilized by the presence of amines, high ammonia concentrations and lower temperatures. Aromatic oxidation products, despite their extremely low volatility, play a minor role in NPF in the chosen urban environment but can be important for particle growth and hence for the survival of newly formed particles. Our measurements quantitatively account for NPF in highly diverse urban environments and explain its large observed variability. Such quantitative information obtained under controlled laboratory conditions will help the interpretation of future ambient observations of NPF rates in polluted atmospheres.

Significance of the organic aerosol driven climate feedback in the boreal area

Abstract: Aerosol particles cool the climate by scattering solar radiation and by acting as cloud condensation nuclei. Higher temperatures resulting from increased greenhouse gas levels have been suggested to lead to increased biogenic secondary organic aerosol and cloud condensation nuclei concentrations creating a negative climate feedback mechanism. Here, we present direct observations on this feedback mechanism utilizing collocated long term aerosol chemical composition measurements and remote sensing observations on aerosol and cloud properties. Summer time organic aerosol loadings showed a clear increase with temperature, with simultaneous increase in cloud condensation nuclei concentration in a boreal forest environment. Remote sensing observations revealed a change in cloud properties with an increase in cloud reflectivity in concert with increasing organic aerosol loadings in the area. The results provide direct observational evidence on the significance of this negative climate feedback mechanism. Vegetation emits organic vapors which can form aerosols in the atmosphere and influence cloud properties. Here, the authors show observational evidence that warmer temperatures lead to increased emissions of these aerosols in boreal forests which cause surface cooling, demonstrating a negative climate feedback mechanism.

Aerosol-boundary-layer-monsoon interactions amplify semi-direct effect of biomass smoke on low cloud formation in Southeast Asia.

Abstract: Low clouds play a key role in the Earth-atmosphere energy balance and influence agricultural production and solar-power generation. Smoke aloft has been found to enhance marine stratocumulus through aerosol-cloud interactions, but its role in regions with strong human activities and complex monsoon circulation remains unclear. Here we show that biomass burning aerosols aloft strongly increase the low cloud coverage over both land and ocean in subtropical southeastern Asia. The degree of this enhancement and its spatial extent are comparable to that in the Southeast Atlantic, even though the total biomass burning emissions in Southeast Asia are only one-fifth of those in Southern Africa. We find that a synergetic effect of aerosol-cloud-boundary layer interaction with the monsoon is the main reason for the strong semi-direct effect and enhanced low cloud formation in southeastern Asia. Biomass burning emissions have been shown to influence clouds in the Atlantic, but its influence in other regions is not well known. Here, the authors show that biomass burning aerosols increase the low-cloud cover over subtropical southeastern Asia by a similar magnitude than over the Atlantic.

Towards understanding the characteristics of new particle formation in the Eastern Mediterranean

Abstract: . To quantify the contribution of new particle formation (NPF) to ultrafine particle number and cloud condensation nuclei (CCN) budgets, one has to understand the mechanisms that govern NPF in different environments and its temporal extent. Here, we study NPF in Cyprus, an Eastern Mediterranean country located at the crossroads of three continents and affected by diverse air masses originating from continental, maritime, and desert-dust source areas. We performed 1-year continuous measurements of aerosol particles down to ∼ 1 nm in diameter for the first time in the Eastern Mediterranean and Middle East (EMME) region. These measurements were complemented with trace gas data, meteorological variables, and retroplume analysis. We show that NPF is a very frequent phenomenon at this site and has higher frequencies of occurrence during spring and autumn. NPF events were both of local and regional origin, and the local events occurred frequently during the month with the lowest NPF frequency. Some NPF events exhibited multiple onsets, while others exhibited apparent particle shrinkage in size. Additionally, NPF events were observed during the nighttime and during episodes of high desert-dust loadings. Particle formation rates and growth rates were comparable to those in urban environments, although our site is a rural one. Meteorological variables and trace gases played a role in explaining the intra-monthly variability of NPF events, but they did not explain why summer months had the least NPF frequency. Similarly, pre-existing aerosol loading did not explain the observed seasonality. The months with the least NPF frequency were associated with higher H 2 SO 4 concentrations but lower NO 2 concentrations, which is an indicator of anthropogenic influence. Air masses arriving from the Middle East were not observed during these months, which could suggest that precursor vapors important for nucleation and growth are transported to our site from the Middle East. Further comprehensive measurements of precursor vapors are required to prove this hypothesis.

Intelligent and Scalable Air Quality Monitoring With 5G Edge

Abstract: Air pollution introduces a major challenge for societies, where it leads to the premature deaths of millions of people each year globally. Massive deployment of air quality sensing devices and data analysis for the resultant data will pave the way for the development of real-time intelligent applications and services, e.g., minimization of exposure to poor air quality either on an individual or city scale. 5G and edge computing supports dense deployments of sensors at high resolution with ubiquitous connectivity, high bandwidth, high-speed gigabit connections, and ultralow latency analysis. This article conceptualizes AI-powered scalable air quality monitoring and presents two systems of calibrating low-cost air quality sensors and the image processing of pictures captured by hyperspectral cameras to better detect air quality. We develop and deploy different AI algorithms in these two systems on a 5G edge testbed and perform a detailed analytics regarding to 1) the performance of AI algorithms and 2) the required communication and computation resources.

The effect of meteorological conditions and atmospheric composition in the occurrence and development of new particle formation (NPF) events in Europe

Abstract: . Although new particle formation (NPF) events have been studied extensively for some decades, the mechanisms that drive their occurrence and development are yet to be fully elucidated. Laboratory studies have done much to elucidate the molecular processes involved in nucleation, but this knowledge has yet to be conclusively linked to NPF events in the atmosphere. There is great difficulty in successful application of the results from laboratory studies to real atmospheric conditions due to the diversity of atmospheric conditions and observations found, as NPF events occur almost everywhere in the world without always following a clearly defined trend of frequency, seasonality, atmospheric conditions, or event development. The present study seeks common features in nucleation events by applying a binned linear regression over an extensive dataset from 16 sites of various types (combined dataset of 85 years from rural and urban backgrounds as well as roadside sites) in Europe. At most sites, a clear positive relation with the frequency of NPF events is found between the solar radiation intensity (up to R2=0.98 ), temperature (up to R2=0.98 ), and atmospheric pressure (up to R2=0.97 ), while relative humidity (RH) presents a negative relation (up to R2=0.95 ) with NPF event frequency, though exceptions were found among the sites for all the variables studied. Wind speed presents a less consistent relationship, which appears to be heavily affected by local conditions. While some meteorological variables (such as the solar radiation intensity and RH) appear to have a crucial effect on the occurrence and characteristics of NPF events, especially at rural sites, it appears that their role becomes less marked at higher average values. The analysis of chemical composition data presents interesting results. Concentrations of almost all chemical compounds studied (apart from O 3 ) and the condensation sink (CS) have a negative relationship with NPF event frequency, though areas with higher average concentrations of SO 2 had higher NPF event frequency. Particulate organic carbon (OC), volatile organic compounds (VOCs), and particulate-phase sulfate consistently had a positive relation with the growth rate of the newly formed particles. As with some meteorological variables, it appears that at increased concentrations of pollutants or the CS, their influence upon NPF frequency is reduced.

A phenomenology of new particle formation (NPF) at 13 European sites

Abstract: . New particle formation (NPF) events occur almost everywhere in the world and can play an important role as a particle source. The frequency and characteristics of NPF events vary spatially, and this variability is yet to be fully understood. In the present study, long-term particle size distribution datasets (minimum of 3 years) from 13 sites of various land uses and climates from across Europe were studied, and NPF events, deriving from secondary formation and not traffic-related nucleation, were extracted and analysed. The frequency of NPF events was consistently found to be higher at rural background sites, while the growth and formation rates of newly formed particles were higher at roadsides (though in many cases differences between the sites were small), underlining the importance of the abundance of condensable compounds of anthropogenic origin found there. The growth rate was higher in summer at all rural background sites studied. The urban background sites presented the highest uncertainty due to greater variability compared to the other two types of site. The origin of incoming air masses and the specific conditions associated with them greatly affect the characteristics of NPF events. In general, cleaner air masses present higher probability for NPF events, while the more polluted ones show higher growth rates. However, different patterns of NPF events were found, even at sites in close proximity ( 200 km), due to the different local conditions at each site. Region-wide events were also studied and were found to be associated with the same conditions as local events, although some variability was found which was associated with the different seasonality of the events at two neighbouring sites. NPF events were responsible for an increase in the number concentration of ultrafine particles of more than 400 % at rural background sites on the day of their occurrence. The degree of enhancement was less at urban sites due to the increased contribution of other sources within the urban environment. It is evident that, while some variables (such as solar radiation intensity, relative humidity, or the concentrations of specific pollutants) appear to have a similar influence on NPF events across all sites, it is impossible to predict the characteristics of NPF events at a site using just these variables, due to the crucial role of local conditions.

The impact of the atmospheric turbulence-development tendency on new particle formation: a common finding on three continents.

Abstract: A new mechanism of new particle formation (NPF) is investigated using comprehensive measurements of aerosol physicochemical quantities and meteorological variables made in three continents, including Beijing, China; the Southern Great Plains site in the USA; and SMEAR II Station in Hyytiala, Finland. Despite the considerably different emissions of chemical species among the sites, a common relationship was found between the characteristics of NPF and the stability intensity. The stability parameter (ζ = Z/L, where Z is the height above ground and L is the Monin-Obukhov length) is found to play an important role; it drops significantly before NPF as the atmosphere becomes more unstable, which may serve as an indicator of nucleation bursts. As the atmosphere becomes unstable, the NPF duration is closely related to the tendency for turbulence development, which influences the evolution of the condensation sink. Presumably, the unstable atmosphere may dilute pre-existing particles, effectively reducing the condensation sink, especially at coarse mode to foster nucleation. This new mechanism is confirmed by model simulations using a molecular dynamic model that mimics the impact of turbulence development on nucleation by inducing and intensifying homogeneous nucleation events.

Ammonium nitrate promotes sulfate formation through uptake kinetic regime

Abstract: . Although the anthropogenic emissions of SO 2 have decreased significantly in China, the decrease in SO 4 2 - in PM 2.5 is much smaller than that of SO 2 . This implies an enhanced formation rate of SO 4 2 - in the ambient air, and the mechanism is still under debate. This work investigated the formation mechanism of particulate sulfate based on statistical analysis of long-term observations in Shijiazhuang and Beijing supported with flow tube experiments. Our main finding was that the sulfur oxidation ratio (SOR) was exponentially correlated with ambient RH in Shijiazhuang (SOR = 0.15 + 0.0032 × exp⁡ ( RH / 16.2 ) ) and Beijing (SOR = - 0.045 + 0.12 × exp⁡ ( RH / 37.8 ) ). In Shijiazhuang, the SOR is linearly correlated with the ratio of aerosol water content (AWC) in PM 2.5 (SOR = 0.15 + 0.40 × AWC / PM 2.5 ). Our results suggest that uptake of SO 2 instead of oxidation of S(IV) in the particle phase is the rate-determining step for sulfate formation. NH 4 NO 3 plays an important role in the AWC and the change of particle state, which is a crucial factor determining the uptake kinetics of SO 2 and the enhanced SOR during haze days. Our results show that NH 3 significantly promoted the uptake of SO 2 and subsequently the SOR, while NO 2 had little influence on SO 2 uptake and SOR in the presence of NH 3 .

Long-term measurement of sub-3 nm particles and their precursor gases in the boreal forest

Abstract: . The knowledge of the dynamics of sub-3nm particles in the atmosphere is crucial for our understanding of first steps of atmospheric new particle formation. Therefore, accurate and stable long-term measurements of the smallest atmospheric particles are needed. In this study, we analyzed over five years of particle concentrations in size classes 1.1–1.3 nm, 1.3–1.7 nm and 1.7–2.5 nm obtained with the Particle Size Magnifier (PSM) and three years of precursor vapor concentrations measured with the Chemical Ionization Atmospheric Pressure Interface Time-of-Flight mass spectrometer (CI-APi-ToF) at the SMEAR II station in Hyytiala, Finland. The results show that the 1.1–1.3 nm particle concentrations have a daytime maximum during all seasons, which is due to increased photochemical activity. There are significant seasonal differences in median concentrations of 1.3–1.7 nm and 1.7–2.5 nm particles, underlining the different frequency of new particle formation between seasons. In particular, concentrations of 1.3–1.7 nm and 1.7–2.5 nm particles are notably higher in spring than during other seasons. Aerosol precursor vapors have notable diurnal and seasonal differences as well. Sulfuric acid and highly oxygenated organic molecule (HOM) monomer concentrations have clear daytime maxima, while HOM dimers have their maxima during the night. HOM concentrations for both monomers and dimers are the highest during summer and the lowest during winter. Higher median concentrations during summer result from increased biogenic activity in the surrounding forest. Sulfuric acid concentrations are the highest during spring and summer, with autumn and winter concentrations being two to three times lower. A correlation analysis between the sub-3nm concentrations and aerosol precursor vapor concentrations indicates that HOMs, particularly their dimers, and sulfuric acid play a significant role in new particle formation in the boreal forest. Our analysis also suggests that there might be seasonal differences in new particle formation pathways that need to be investigated further.

A 3D study on the amplification of regional haze and particle growth by local emissions

Abstract: The role of new particle formation (NPF) events and their contribution to haze formation through subsequent growth in polluted megacities is still controversial. To improve the understanding of the sources, meteorological conditions, and chemistry behind air pollution, we performed simultaneous measurements of aerosol composition and particle number size distributions at ground level and at 260 m in central Beijing, China, during a total of 4 months in 2015–2017. Our measurements show a pronounced decoupling of gas-to-particle conversion between the two heights, leading to different haze processes in terms of particle size distributions and chemical compositions. The development of haze was initiated by the growth of freshly formed particles at both heights, whereas the more severe haze at ground level was connected directly to local primary particles and gaseous precursors leading to higher particle growth rates. The particle growth creates a feedback loop, in which a further development of haze increases the atmospheric stability, which in turn strengthens the persisting apparent decoupling between the two heights and increases the severity of haze at ground level. Moreover, we complemented our field observations with model analyses, which suggest that the growth of NPF-originated particles accounted up to ∼60% of the accumulation mode particles in the Beijing–Tianjin–Hebei area during haze conditions. The results suggest that a reduction in anthropogenic gaseous precursors, suppressing particle growth, is a critical step for alleviating haze although the number concentration of freshly formed particles (3–40 nm) via NPF does not reduce after emission controls.

Aerosol particle formation in the upper residual layer

Abstract: . According to current estimates, atmospheric new particle formation (NPF) produces a large fraction of aerosol particles and cloud condensation nuclei in the Earth's atmosphere, which have implications for health and climate. Despite recent advances, atmospheric NPF is still insufficiently understood in the lower troposphere, especially above the mixed layer (ML). This paper presents new results from co-located airborne and ground-based measurements in a boreal forest environment, showing that many NPF events ( ∼42 %) appear to start in the topmost part of the residual layer (RL). The freshly formed particles may be entrained into the growing mixed layer (ML) where they continue to grow in size, similar to the aerosol particles formed within the ML. The results suggest that in the boreal forest environment, NPF in the upper RL has an important contribution to the aerosol load in the boundary layer (BL).

Fire and vegetation dynamics in northwest Siberia during the last 60 years based on high-resolution remote sensing

Abstract: . The rapidly warming Arctic undergoes transitions that can influence global carbon balance. One of the key processes is the shift towards vegetation types with higher biomass underlining a stronger carbon sink. The shift is predicted by bioclimatic models based on abiotic climatic factors, but it is not always confirmed with observations. Recent studies highlight the role of disturbances in the shift. Here we use high-resolution remote sensing to study the process of transition from tundra to forest and its connection to wildfires in the 20 000 km2 area in northwest Siberia. Overall, 40 % of the study area was burned during a 60-year period. Three-quarters of the burned areas were dry tundra. About 10 % of the study area experienced two–three fires with an interval of 15–60 years suggesting a shorter fire return interval than that reported earlier for the northern areas of central Siberia (130–350 years). Based on our results, the shift in vegetation (within the 60-year period) occurred in 40 %–85 % of the burned territories. All fire-affected territories were flat; therefore no effect of topography was detected. Oppositely, in the undisturbed areas, a transition of vegetation was observed only in 6 %–15 % of the territories, characterized by steeper topographic slopes. Our results suggest a strong role of disturbances in the tree advance in northwest Siberia.

Transit Pollution Exposure Monitoring using Low-Cost Wearable Sensors

Abstract: Transit activities are a significant contributor to a person’s daily exposure to pollutants. Currently obtaining accurate information about the personal exposure of a commuter is challenging as existing solutions either have a coarse monitoring resolution that omits subtle variations in pollutant concentrations or are laborious and costly to use. We contribute by systematically analysing the feasibility of using wearable low-cost pollution sensors for capturing the total exposure of commuters. Through extensive experiments carried out in the Helsinki metropolitan region, we demonstrate that low-cost sensors can capture the overall exposure with sufficient accuracy, while at the same time providing insights into variations within transport modalities. We also demonstrate that wearable sensors can capture subtle variations caused by differing routes, passenger density, location within a carriage, and other factors. For example, we demonstrate that location within the vehicle carriage can result in up to 25 % increase in daily pollution exposure – a significant difference that existing solutions are unable to capture. Finally, we highlight the practical benefits of low-cost sensors as a pollution monitoring solution by introducing applications that are enabled by low-cost wearable sensors.

Influence of vegetation on occurrence and time distributions of regional new aerosol particle formation and growth

Abstract: . The occurrence frequency of regional atmospheric new aerosol particle formation and consecutive growth events ( fNPF ) were studied with respect to vegetation activity, aerosol properties, air pollutants and meteorological data in Budapest over the time interval from 2008 to 2018. The data set evaluated contained results of in situ measurements on the land surface that were mostly performed at the Budapest platform for Aerosol Research and Training Laboratory, of satellite-based products recorded by MODIS on Terra and of modelled vegetation emission-related properties from an advanced regional biogeochemical model. The annual mean relative occurrence frequencies were considerable (with an overall mean of 21 %), remained at a constant level (with an overall SD of 5 %) and did not exhibit tendentious change over the years. The shape of the distributions of monthly mean fNPF exhibited large variability from year to year, while the overall average distribution already possessed a characteristic pattern. The structure of the new particle formation (NPF) occurrence distributions was compared to those of environmental variables including concentrations of gas-phase H2SO4 , SO2 , O3 , NO, NO2 , CO, PM10 mass and NH3 ; particle numbers in the size fractions of 6–1000, 6–100 and 100–1000 nm ; condensation sink; air temperature ( T ); relative humidity (RH); wind speed (WS); atmospheric pressure ( P ); global solar radiation (GRad); gross primary production (GPP) of vegetation; leaf area index (LAI); and stomatal conductance (SCT). There were no evident systematic similarities between fNPF on the one hand and all of the variables studied on the other hand, except for H2SO4 and perhaps NH3 . The spring maximum in the NPF occurrence frequency distribution often overlapped with the time intervals of positive T anomaly in vegetated territories. The link between the potential heat stress exerted on plants in sultry summer intervals and the summer fNPF minimum could not be proven. The relevance of environmental variables was assessed by their ratios on NPF event days and on non-event days. The gas-phase H2SO4 concentration showed the largest monthly ratios, followed by O3 . The WS, biogenic precursor gases and SO2 can generally favour NPF events, although their influence seemed to be constrained. An association between the fNPF and vegetation growth dynamics was clearly identified.

Measurement report: The influence of traffic and new particle formation on the size distribution of 1-800 nm particles in Helsinki - a street canyon and an urban background station comparison

Abstract: . Most of the anthropogenic air pollution sources are located in urban environments. The contribution of these sources to the population of atmospheric particles in the urban environment is poorly known. In this study, we investigated the aerosol particle number concentrations in a diameter range from 1 to 800 nm at a street canyon site and at a background station within 1 km from each other in Helsinki, Finland. We use these number size distribution data together with complementary trace gas data and develop a method to estimate the relative contributions of traffic and atmospheric new particle formation (NPF) to the concentrations of sub-3 nm particles. During the daytime, the particle concentrations were higher at the street canyon site than at the background station in all analyzed modes: sub-3 nm particles, nucleation mode (3–25 nm), Aitken mode (25–100 nm), and accumulation mode (100–800 nm). The population of sub-3 nm and nucleation mode particles was linked to local sources such as traffic, while the accumulation mode particles were more related to non-local sources. Aitken mode particles were dominated by local sources at the street canyon site, while at the background station they were mainly influenced by non-local sources. The results of this study support earlier research showing direct emissions of the sub-3 nm particles from traffic. However, by using our new method, we show that, during NPF events, traffic contribution to the total sub-3 nm particle concentration can be small and during daytime (6:00–20:00) in spring it does not dominate the sub-3 nm particle population at either of the researched sites. In the future, the contribution of traffic to particle number concentrations in different urban environments can be estimated with a similar approach, but determining the relationships between the gas and particle concentrations from observations needs to be conducted with longer data sets from different urban environments.

Research agenda for the Russian Far East and utilization of multi-platform comprehensive environmental observations

Abstract: The Russian Far East is a region between China and the Russian Arctic with a diverse climatological, geophysical, oceanic, and economical characteristic. The southern region is located in the Far E...

Atmospheric gaseous hydrochloric and hydrobromic acid in urban Beijing, China: detection, source identification and potential atmospheric impacts

Abstract: . Gaseous hydrochloric (HCl) and hydrobromic acid (HBr) are vital halogen species that play essential roles in tropospheric physicochemical processes. Yet, the majority of the current studies on these halogen species were conducted in marine or coastal areas. Detection and source identification of HCl and HBr in inland urban areas remain scarce, thus limiting the full understanding of halogen chemistry and potential atmospheric impacts in the environments with limited influence from the marine sources. Here, both gaseous HCl and HBr were concurrently measured in urban Beijing, China, during winter and early spring of 2019. We observed significant HCl and HBr concentrations ranging from a minimum value at 1 × 10 8 molecules cm −3 (4 ppt) and 4 × 10 7 molecules cm −3 (1 ppt) up to 6 × 10 9 molecules cm −3 (222 ppt) and 1 × 10 9 molecules cm −3 (37 ppt), respectively. The HCl and HBr concentrations are enhanced along with the increase of atmospheric temperature, UVB and levels of gaseous HNO 3 . Based on the air mass analysis and high correlations of HCl and HBr with the burning indicators (HCN and HCNO), gaseous HCl and HBr are found to be related to anthropogenic burning aerosols. The gas–particle partitioning may also play a dominant role in the elevated daytime HCl and HBr. During the daytime, the reactions of HCl and HBr with OH radicals lead to significant production of atomic Cl and Br, up to 2 × 10 4 molecules cm −3 s −1 and 8 × 10 4 molecules cm −3 s −1 , respectively. The production rate of atomic Br (via HBr + OH) is 2–3 times higher than that of atomic Cl (via HCl + OH), highlighting the potential importance of bromine chemistry in the urban area. On polluted days, the production rates of atomic Cl and Br are faster than those on clean days. Furthermore, our observations of elevated HCl and HBr may suggest an important recycling pathway of halogen species in inland megacities and may provide a plausible explanation for the widespread halogen chemistry, which could affect the atmospheric oxidation in China.