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There has been controversy regarding the air pollutants emitted from sources closely related to the activities of daily life in China, such as cooking, setting off fireworks, sacrificial incense and joss paper burning, and barbecue (which have been named the five missing sources – FMSs), and the extent to which they impact the outdoor air quality. To date, due to the lack of both an activity dataset and emission factors, there have been no estimations of the emission of air pollutants from FMSs. In this work, we have attempted to combine questionnaire data, various statistical data, and data on points of interest to obtain a relatively complete set of activity data. The emission factors (EFs) of carbonaceous aerosols were tested in our lab. Emission inventories of carbonaceous aerosols with a high spatial–temporal resolution for FMSs were then established, and the spatial variation trend and driving forces were discussed. From 2000 to 2018, organic carbon (OC) emissions were in the range of 4268–4919 t. OC emissions from FMSs were between 1.5 ‰ and 2.2 ‰ of the total emissions in China. Black carbon (BC), elemental carbon (EC), and brown carbon (BrC) absorption cross-section (ACSBrC) emissions from FMSs were in the ranges of 22.6–43.9 t, 213–324 t, and 14.7–35.6 Gm2, respectively. Their emissions tended to be concentrated in certain periods and areas. The OC emission intensities in central urban areas were 3.85–50.5 times those in rural areas (due to the high density of human activity), while the ACSBrC emissions in rural regions accounted for 63.0–79.5 % of the total emissions (resulting from uncontrolled fireworks). A mass of fireworks led to much higher ACSBrC and EC emissions on Chinese New Year's Eve, with respective values that were 1444 and 262 times their corresponding yearly averages. Significant (p<0.01) correlations between the population's income and pollutant emissions were also found: these correlations were positive (r=0.94) and negative (r=-0.94) for urban and rural regions, respectively, indicating the necessity to regulate residents' lifestyles and increase residents' income in respective urban and rural regions. This study provides firsthand data to identify emissions, variation trends, and impacting factors from the FMSs. This is helpful for modeling works on air quality, the climate effect, and human health risks during specific periods or in specific regions as well as for modifying emission control policies. The data compiled in this work can found at https://doi.org/10.6084/m9.figshare.19999991.v2 (Cheng et al., 2022).

As an important issue in atmospheric environment, the contributions of anthropogenic emissions and meteorological conditions to air pollution have been little assessed over receptor regions in regional transport of air pollutants. In the present study of 5-year observations and modeling, we targeted the Twain-Hu Basin (THB), a large region of heavy PM2.5 pollution in central China, to assess the effects of meteorology on PM2.5 change over a receptor region in the regional transport of air pollutants. Based on observations of environment and meteorology over 2015–2019, the Kolmogorov–Zurbenko (KZ) filter was performed to decompose the PM2.5 variations into multiple timescale components over the THB, where the short-term, seasonal and long-term components accounted for, respectively, 47.5 %, 41.4 % and 3.7 % of daily PM2.5 changes. The short-term and seasonal components dominated the day-to-day PM2.5 variations with long-term component determining the change trend of PM2.5 concentrations over recent years. As the emission- and meteorology-related long-term PM2.5 components over the THB were identified, the meteorological contribution to the declining PM2.5 trend presented a distinct spatial pattern over the THB with northern positive rates up to 61.92 % and southern negative rates down to −24.93 %. The opposite effects of meteorology on PM2.5 pollution could accelerate and offset the effects of emission reductions in the northern and southern THB, which is attributed to the upwind diffusion and downward accumulation of air pollutants over receptor regions in regional PM2.5 transport. It is noteworthy that the increasing conversion efficiencies of SO2 and NO2 to sulfate and nitrate for secondary PM2.5 could have offset the effect of PM2.5 emission reduction on air pollution in the THB during recent years, revealing the enhancing contribution of gaseous precursor emissions to PM2.5 concentrations under control of anthropogenic emissions of PM2.5 and the gaseous precursors over receptor regions in the regional transport of air pollutants. Our results highlight the effects of emission mitigation and meteorological changes on the source–receptor relationship of the regional transport of air pollutants with the implication of long-range transport of air pollutants for regional and global environment changes.

PM2.5 concentrations in Wuhan, China decreased by 36.0% between the period prior to the COVID-19 pandemic (1–23 January, 2020) and the COVID-lockdown period (24 January to 29 February, 2020). However, decreases in PM2.5 concentration due to regional PM2.5 transport driven by meteorological changes, and the relationship between the PM2.5 source and receptor, are poorly understood. Therefore, this study assessed how changes in meteorology, local emissions, and regional transport from external source emissions contributed to the decrease in Wuhan's PM2.5 concentration, using FLEXPART-WRF and WRF-Chem modelling experiments. The results showed that meteorological changes in central China explain up to 22.2% of the total decrease in PM2.5 concentrations in Wuhan, while the remaining 77.8% was due to air pollutant emissions reduction. Reduction in air pollutant emissions depended on both local and external sources, which contributed alomst equally to the reduction in PM2.5 concentrations (38.7% and 39.1% of the total reduction, respectively). The key emissions source areas affecting PM2.5 in Wuhan during the COVID-lockdown were identified by the FLEXPART-WRF modeling, revealing that regional-joint control measures in key areas accounted for 89.3% of the decrease in PM2.5 concentrations in Wuhan. The results show that regional-joint control can be enhanced by identifying key areas of emissions reduction from the source–receptor relationship of regional PM2.5 transport driven by meteorology under the background of East Asian monsoon climate change.

Global tropospheric nitrogen dioxide (NO2) changes have different or even opposite impacts on the photochemical formation of ozone in different regions under different weather and emission condition. However, the changes over regions affected by different levels of human activities are not well known. By using the Ozone Monitoring Instrument (OMI) measurements, we analyzed spatial and temporal variability of tropospheric NO2 vertical column densities (VCDs) from the megacity to the background regions during 2005–2019. Consistent with previous research, our results show a rapid decline of tropospheric NO2 column density over regions strongly affected by human activities, especially for source regions. The decline rates of annual mean NO2 VCDs are up to − 2.44% year−1, − 2.37% year−1, and − 1.43% year−1 over megacities of the USA, Europe, and China, respectively. However, the decreasing rate has slowed, and even reversed to an increasing trend, of tropospheric NO2 from megacities to developing and remote regions, especially over ocean and background areas less affected by anthropogenic activity. From 2005 to 2019, the NO2 VCDs over the ocean and background areas increased for all seasons, with the statistically significant (p

The light-absorbing organic aerosol (OA) constitutes an important fraction of absorbing components, counteracting major cooling effect of aerosols to climate. The mechanisms in linking the complex and changeable chemistry of OA with its absorbing properties remain to be elucidated. Here, by using solvent extraction, ambient OA from an urban environment was fractionated according to polarity, which was further nebulized and online characterized with compositions and absorbing properties. Water extracted high-polar compounds with a significantly higher oxygen to carbon ratio (O/C) than methanol extracts. A transition O/C of about 0.6 was found, below and above which the enhancement and reduction of OA absorptivity were observed with increasing O/C, occurring on the less polar and high polar compounds, respectively. In particular, the co-increase of nitrogen and oxygen elements suggests the important role of nitrogen-containing functional groups in enhancing the absorptivity of the less polar compounds (e.g., forming nitrogen-containing aromatics), while further oxidation (O/C0.6) on high-polar compounds likely led to fragmentation and bleaching chromophores. The results here may reconcile the previous observations about darkening or whitening chromophores of brown carbon, and the parametrization of O/C has the potential to link the changing chemistry of OA with its polarity and absorbing properties.

The less improvement of ambient visibility suspects the government’s efforts on alleviating PM2.5 pollution. The COVID-19 lockdown reduced PM2.5 and increased visibility in Wuhan. Compared to pre-lockdown period, the PM2.5 concentration decreased by 39.0 μg m−3, dominated by NH4NO3 mass reduction (24.8 μg m−3) during lockdown period. The PM2.5 threshold corresponding to visibility of 10 km (PTV10) varied in 54–175 μg m−3 and an hourly PM2.5 of 54 μg m−3 was recommended to prevent haze occurrence. The lockdown measures elevated PTV10 by 9–58 μg m−3 as the decreases in PM2.5 mass scattering efficiency and optical hygroscopicity. The visibility increased by 107%, resulted from NH4NO3 extinction reduction. The NH4NO3 mass reduction weakened its mutual promotion with aerosol water and increased PM2.5 deliquescence humidity. Controlling TNO3 (HNO3 + NO3−) was more effective to reduce PM2.5 and improve visibility than NHx (NH3 + NH4+) unless the NHx reduction exceeded 11.7–17.5 μg m−3.

China has enacted the "Clean Heating" (CH) policy in north China. The domain-specific impacts on PM

There has been controversy about the air pollutants emitted from sources closely related to people's daily life (such as cooking, fireworks burning, sacrificial incenses and joss paper burning, and barbecue, named as five missing sources, FMS) impacting the outdoor air quality to what extent. Till now, there is no emission estimation of air pollutants from FMS, as the missing of both activity dataset and emission factors. We attempted to combine the questionnaire data, various statistical data, and data of points of interest to obtain a relatively complete set of activity data. The emission factors (EFs) of carbonaceous aerosols were tested in our lab. Then, the emission inventories of carbonaceous aerosol with the high spatial-temporal resolution for FMS were established firstly, and the spatial-variation trend and driving forces were discussed. From 2000 to 2018, organic carbon (OC) increased from 4268 t to 4919 t. The OC emission from FMS was 1.48–2.18 ‰ of its total emission in China. The emissions of black carbon, element carbon (EC), and brown carbon absorption cross-section (ACSBrC) emissions from FMS were in the ranges of 22.6–43.9 t, 213–324 t, and 14.7–35.6 Gm2, respectively. Their emissions tended to concentrate in special periods and areas. The OC emission intensities in central urban areas were 3.85–50.5 times that of rural areas due to the high density of human activities. While the ACSBrC emissions in rural regions accounted for 63.0–79.5 % of the total emission result from uncontrolled fireworks burning. A mass of fireworks burning led to extremely higher ACSBrC and EC emissions on Chinese New Year’s eve, as 1444 and 262 times their corresponding yearly average values. Interestingly, significant (p

Regional PM

Summertime ozone pollution has become increasingly severe over many parts of China in recent years. Due to lack of historical ozone observations, few studies have analyzed the linkage between natural climate variability and ozone levels for a long time series. This study uses the simulation datasets from CMIP6 to explore the effects of El Niño-Southern Oscillation (ENSO) on summertime (June/July/August) surface ozone concentrations in central-eastern China (CEC; 20°N-42°N, 100°E-123°E) during the period of 1950-2014. Our results show that, after excluding the emission-related trend, the detrended summertime daily mean surface ozone concentrations averaged over CEC in El Niño years (30.69 ppb) are higher than those in La Niña events (29.34 ppb). Compared to the summertime mean ozone of 1950-2014 (30.25 ppb), the maximum anomalies in CMIP6 are 2.88 ppb (9.52% higher) and - 5.52 ppb (18.25% lower) in El Niño and La Niña years, respectively. In addition, the summertime MDA8 ozone of CEC is significantly correlated with the central-eastern equatorial Pacific SST (5°N-5°S, 170°W-120°W) (R = 0.29, P-value = 0.02). Such ozone increases/declines in El Niño/La Niña years are also found in satellite observations of OMI ozone. The results show that the ENSO affects the large-scale circulations over central-eastern China, which regulate the regional atmospheric stability and meteorological conditions (including horizontal wind fields, geopotential height, vertical velocity, surface air temperature, and precipitation) to influence the efficiency of ozone photochemical formation and transport. Our study makes better estimation and attribution of future surface ozone pollution in China.

Emissions of light-absorbing black carbon (BC) and organic aerosol (OA) from biomass burning are presented as complex mixtures, which introduce challenges in modeling their absorbing properties. In this study, we chose typical residential wood burning emission and used a novel designed chamber to investigate the early stage evolution of plumes from different burning phases under real ambient conditions. The detailed mixing state between BC and OA was evaluated, on the basis of which optical modeling was performed to achieve a closure of aerosol-absorbing properties. Intensive secondary OA (SOA) formation was observed under solar radiation. OA from flaming conditions showed a higher absorptivity than from smoldering conditions, as OA is mostly internally and externally mixed with BC, respectively. For flaming (smoldering), the imaginary refractive index of OA (kOA) was initially at 0.03 ± 0.01 (0.001) and 0.15 ± 0.02 (0.05 ± 0.02) at λ = 781 and 405 nm, respectively, with a half-decay time of 2-3 h in light but a

Currently, mitigating severe particle pollution in autumn and winter is the key to further improving the air quality of China. The source contributions and transboundary transport of fine particles (PM2.5) in pollution episodes are closely related to large-scale or synoptic-scale atmospheric circulation. How to effectively reduce emissions to control haze pollution under different synoptic conditions is rarely reported. In this study, we classify the synoptic conditions over central China from 2013 to 2018 by using Lamb–Jenkinson method and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Final (FNL) operational global analysis data. The effectiveness of emission control to reduce PM2.5 pollution during winter haze episodes under potential synoptic controls is simulated by GEOS-Chem model. Among the 10 identified synoptic patterns, four types account for 87 % of the total pollution days. Two typical synoptic modes are characterized by low surface wind speed and stable weather conditions or high relative humidity (A or C type) over central China due to a high-pressure system or a southwest trough and low-pressure system, blocking pollutants dispersion. Sensitivity simulations show that these two heavy pollution processes are mainly contributed by local emission sources with ∼82 % for A type and ∼85 % for C type, respectively. The other two patterns lead to pollution of transport characteristics affected by northerly or southerly winds (NW or SW type), carrying air pollution from northern or southern China to central China. The contribution of pollution transmission from northern and southern China is 36.9 % and 7.6 %, respectively of PM2.5, and local emission sources contribute 41 % and 69 %, respectively. We also estimate the effectiveness of emission reduction in these four typical severe pollution synoptic processes. By only reducing SO2 and NOx emission and not controlling NH3, the enhanced nitrate counteracts the effect of sulfate reduction on PM2.5 mitigation, with a less than 4 % decrease in PM2.5. In addition, to effectively mitigate haze pollution of NW- and SW-type synoptic-controlled episodes, local emission control actions should be in coordination with regional collaborative actions.

Stringent pollution control measures are generally applied to improve air quality, especially in the Spring Festival in China. Meanwhile, human activities are reduced significantly due to nationwide lockdown measures to curtail the COVID-19 spreading in 2020. Herein, to better understand the influence of control measures and meteorology on air pollution, this study compared the variation of pollution source and their health risk during the 2019 and 2020 Spring Festival in Linfen, China. Results revealed that the average concentration of PM

The secondary production of oxygenated organic aerosol (OOA) impacts air quality, climate, and human health. The importance of various sources in contributing to the OOA loading and associated different ageing mechanisms remains to be elucidated. Here we present a concurrent observation and factorization analysis on the mass spectra of organic aerosol (OA) by a high-resolution aerosol mass spectrometer and volatile organic compounds (VOCs) by a proton transfer reaction mass spectrometer in Wuhan, a megacity in central China, during autumn. The full mass spectra of organics with two principle anthropogenic sources were identified as the traffic and cooking sources, for their primary emission profiles in aerosol and gas phases, the evolutions, and their respective roles in producing OOA and secondary VOCs. Primary emissions in gas and aerosol phases both contributed to the production of OOA. The photooxidation of traffic sources from the morning rush hour caused a 2.5 fold increase in OOA mass in a higher oxidation state (oxygen-to-carbon ratio as O/C =0.72), co-producing gas phase carboxylic acids, while, at night, cooking aerosols and VOCs (particularly acrolein and hexanal) importantly caused the nocturnal formation of oxygenated intermediate VOCs, increasing OOA mass by a factor of 1.7 (O/C =0.42). The daytime and nighttime formation of secondary aerosols, as contributed by different sources, was found to be modulated by solar radiation and air moisture, respectively. The environmental policy should, therefore, consider the primary emissions and their respective ageing mechanisms influenced by meteorological conditions.

The regional transport of air pollutants, controlled by emission sources and meteorological factors, results in a complex source–receptor relationship of air pollution change. Wuhan, a metropolis in the Yangtze River middle basin (YRMB) of central China, experienced heavy air pollution characterized by hourly PM2.5 concentrations reaching 471.1 µg m−3 in January 2016. To investigate the regional transport of PM2.5 over central eastern China (CEC) and the meteorological impact on wintertime air pollution in the YRMB area, observed meteorological and other relevant environmental data from January 2016 were analyzed. Our analysis presented noteworthy cases of heavy PM2.5 pollution in the YRMB area with unique “non-stagnant” meteorological conditions of strong northerly winds, no temperature inversion, and additional unstable structures in the atmospheric boundary layer. This unique set of conditions differed from the stagnant meteorological conditions characterized by near-surface weak winds, air temperature inversion, and stable structure in the boundary layer that are typically observed in heavy air pollution over most regions in China. The regional transport of PM2.5 over CEC aggravated PM2.5 levels, thus creating heavy air pollution in the YRMB area. This demonstrates a source–receptor relationship between the originating air pollution regions in CEC and the receiving YRMB region. Furthermore, a backward trajectory simulation using a Flexible Particle dispersion (FLEXPART) Weather Research and Forecasting (WRF) model to integrate the air pollutant emission inventory over China was used to explore the patterns of regional transport of PM2.5 governed by the strong northerly winds in the cold air activity of the East Asian winter monsoon season. It was estimated that the regional transport of PM2.5 from non-local air pollutant emissions contributes more than 65 % of the PM2.5 concentrations to the heavy air pollution in the YRMB region during the study period, revealing the importance of the regional transport of air pollutants over China as a causative factor of heavy air pollution over the YRMB area.

Sub-type source profiles for atmospheric fine particle (PM2.5) were still scare in China, which limited the accurate source identification of it. Fugitive dust (including road dust, soil dust, resuspended dust, and construction dust, etc.) was one type of the most important contributors to PM2.5 and its associated toxic metals held potential threaten to human health. The chemical compositions, sources, and health risks of sub-type fugitive dust deserved an investigation for further accurate control of particles and alleviating human health risks. A total of sixty-five fugitive dust samples were collected in Suzhou, a fast-developing city in southern China, including eleven sub-types of road dust (overpass, main street, collector street, and ordinary street), soil dust (farmland and tree lawn), resuspended dust (site types were corresponding to those of road dust), and construction dust (large construction sites). Chemical analysis of water-soluble ions, elements, and carbonaceous components was carried out to establish the sub-type source profiles of PM2.5 for fugitive dust. Results showed that crustal elements were the most abundant components of fugitive dust, and soil dust was less polluted by anthropogenic activities. High contents of OC and low contents of EC were found in all the eleven types of dust. Equivalent ratios of anions and cations indicated that the fugitive dust was obviously alkaline. The contents of OC and EC in the four types of road dust were higher than those in other types of dust, while there existed differences among the sub-types of road dust. The NO3-/SO42- ratios (0.03-0.09) implied that coal-burning and motor vehicle emission co-existed in Suzhou. Coefficient divergence (CD) values of eleven sub-type source profiles showed that there were certain differences among them, which suggested the possibility of sub-type source identification. Cluster analysis indicated the heavy metals in fugitive dust were mainly from crustal materials, metallurgical manufacturing, vehicle emissions, and industrial activities. The enrichment degree of heavy metals for the four types of road dust was also inconsistent. Heavy metals in road dust and soil dust posed a non-carcinogenic risk to children through direct ingestion, and the non-carcinogenic risk of direct intake of heavy metals was much higher than that of respiratory and skin contact. It was found that the accumulative health risks of heavy metals were higher in densely populated areas, traffic intensive areas, and industrial areas through the spatial analysis. This study firstly discussed the chemical compositions of PM2.5 for eleven sub-types of fugitive dust in a Chinese city and assessed the accumulative health risks of heavy metals, which could be a demonstration for further related researches.

Ammonia emission reduction is increasingly being considered one of the control measures to mitigate wintertime fine particulate matter (PM

Atmospheric lead (Pb) pollution has attracted long-term and widespread concerns due to its high toxicity. The definite source identification of atmospheric Pb is the key step to mitigate this pollution. Here, we first report an overlooked source of atmospheric nanosized Pb particles using transmission electron microscopy and bulk sample analyses, finding that residential honeycomb briquette combustion emits large numbers of nanosized Pb-rich particles. We found that 33.7 ± 19.9 % of primary particles by number from residential honeycomb briquette combustion contains the crystalline Pb particles. These Pb-rich particles range in size from 14 to 956 nm with a mean diameter of 117 nm. Compared with raw coal chunks, honeycomb briquette combustion could emit less carbonaceous particles, but largely increase nanosized Pb particle emissions. This result is attributed to two key factors: (1) higher Pb content in honeycomb briquette (63.6 μg g

The extent of PM2.5 pollution has reduced in traditional polluted regions such as the North China Plain (NCP), Yangtze River Delta (YRD), Sichuan Basin (SB), and Pearl River Delta (PRD) over China in recent years. Despite this, the Twain-Hu Basin (THB), which covers the lower flatlands in Hubei and Hunan provinces in central China, was found to be a high PM2.5 pollution region, with annual mean PM2.5 concentrations of 41–63 μg·m−3, which is larger than the values in YRD, SB, and PRD during 2014–2019, and high aerosol optical depth values (>0.8) averaged over 2000–2019 from the MODIS products. Heavy pollution events (HPEs) are frequently observed in the THB, with HPE-averaged concentrations of PM2.5 reaching up to 183–191 μg·m−3, which exceeds their counterparts in YRD, SB, and PRD for 2014–2019, highlighting the THB as a center of heavy PM2.5 pollution in central China. During 2014–2019, approximately 65.2% of the total regional HPEs over the THB were triggered by the regional transport of PM2.5 over Central and Eastern China (CEC). This occurred in view of the co-existing HPEs in the NCP and the THB, with a lag of almost two days in the THB-PM2.5 peak, which is governed by the strong northerlies of the East Asian monsoon (EAM) over CEC. Such PM2.5 transport from upstream source regions in CEC contributes 60.3% of the surface PM2.5 pollution over the THB receptor region. Hence, a key PM2.5 receptor of the THB in regional pollutant transport alters the distribution patterns of PM2.5 pollution over China, which is attributable to the climate change of EAMs. This study indicates a complex relationship between sources and receptors of atmospheric aerosols for air quality applications.

The importance of regional air pollutant transport modulated by large-scale synoptic circulation has been poorly understood for air pollution. In the present study of 5-year (2015-2019) observation...