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Researchers have warned that the paradigm about who should measure air quality (AQ) in cities can change as low-cost commercial sensors for monitoring atmospheric composition gain global popularity. The new paradigm implies the expansion of the traditionally governmental responsibilities for AQ monitoring (to collect, interpret, and explain the data) to previously uninvolved actors. This study reports a first practical example of such changed AQ paradigm that occurred in a large industrial city of Krasnoyarsk (Russia). We describe how severe problems with urban AQ and a limited access to the AQ data from governmental sensors triggered decentralization of the AQ monitoring in the city. The decentralization is manifested by the fact that both governmental network and crowdfund-based activist AQ network, are being used for scientific and, to some extent, advisory purposes. The decentralization was foremost established due to the ambiguous quantitative information about AQ provided to users by the governmental network, exacerbated by efficient alternatives for alleviating this gap, offered by the activists. The unique decentralization of AQ monitoring in Krasnoyarsk can transform into the synergy between the government and citizen action aimed on easing air pollution as the governmental organizations can efficiently reinforce the resources (funds and manpower), and provide legal and technical support, while civic action groups with established audience can consolidate targeted groups of citizens for formulating efficient city-wide strategies in AQ management. Such synergy can become an inspiring example for the cities with degraded AQ, where the official monitoring is plagued by financial or technological limitations. • First example on how air quality (AQ) monitoring paradigm changed by cheap AQ nodes. • In Krasnoyarsk, some governmental AQ functions were replaced by AQ activists. • Government provided ambiguous AQ info; it undermined credibility of their AQ system. • Activists filled this gap: cheap nodes use, open access and use of social networks. • Synergies between government and activists for filling AQ information gaps proposed. [ABSTRACT FROM AUTHOR]

The Yellow Sea serves as a pathway for air pollution transport from the Asian continent into Korea and is annually monitored by the Korean Meteorological Administration (KMA) research vessel during the spring season. This study investigated the spatio-temporal variation of long-range transported greenhouse gases (CO 2 and CH 4) and air pollutants (CO, NO x , SO 2 , O 3) in the Yellow Sea during the Yellow Sea Air Quality (YES-AQ) campaign. Our analysis reveals that GHGs and air pollutants exhibit a clear latitudinal distribution. Lower concentrations are observed in the range of 31.2–34.5°N, primarily influenced by air masses traversing the ocean and the western part of Korean Peninsula. In contrast, higher concentrations occur more frequently at 34.5–37.8°N, primarily affected by continental air masses. The regression slopes of CO and CO 2 vary depending on regional characteristics, particularly in air originating from Korea and China. Regression slope analysis between CO, CO 2, and CH 4 , except for high plume of CH 4 (>2.05 ppm), indicates that fossil fuel sources play a significant role. A high plume of CH 4 (>2.05 ppm) was observed on April 22nd, coinciding with the maximum O 3 concentrations during the period of highest temperatures throughout the voyage. The potential source regions were identified in the west-southern coast of Korea, using footprint analysis from Stochastic Time-Inverted Lagrangian Transport (STILT) and column-averaged dry-air mole fraction of CH 4 (XCH 4) retrieval from the TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor (S5P) satellite. The high CH 4 enhancements are most likely due to biogenic emissions triggered by favorable near-surface temperatures for microbial activities in soil. Furthermore, the high CH 4 enhancements were not correlated with CO and CO 2 , indicating that the source was not related to fossil fuel combustion. On March 29–30, a high plume of NO x was detected and is likely attributed to the Bohai Sea, which is located just above the Yellow Sea and surrounded by highly industrialized and semi-enclosed areas. • Yellow Sea Air Quality campaign studies greenhouse/air pollutants distribution. • Greenhouse/air pollutants show a clear latitudinal gradient over Yellow Sea. • CO, CO 2 , CH 4 correlation suggests fossil fuel-based sources mainly from China and Korea. • Highly elevated CH 4 linked to microbial-related biogenic emissions from Korean based on STILT analysis. [ABSTRACT FROM AUTHOR]

To understand the changes in CH 4 emissions in East Asia, mainly in China, we analyzed the synoptic scale variability (SSV) of CO 2 and CH 4 mole fractions at Anmyeondo (AMY; 36.53°N, 126.32°E, 46 m above sea level) in South Korea using near-surface in-situ observations and an atmospheric chemical transport model (ACTM) to investigate the role of prescribed surface fluxes on SSV. The SSV of the tracers at AMY was mainly caused by emission variations from eastern and northeastern China during the winters in 2010–2020, as indicated by the simulated concentration footprints at AMY observed using the WRF-STILT model. The estimated SSV of ΔCH 4 /ΔCO 2 mole fraction ratios from the observations was 4.2–6.2 ppb ppm−1, with a mean of 5.7 ± 0.93 ppb ppm−1 during the winters in 2010–2020. We also calculated the CH 4 /CO 2 emission ratio from China's total annual fossil-fuel emissions, excluding seasonal sources estimated from the Emission Database for Global Atmospheric Research. We found that the ratio was overestimated by ∼98.1% compared to observations, which was likely driven either due to the overestimation of CH 4 or underestimation of CO 2. We discerned that the model-simulated SSV of the ΔCH 4 /ΔCO 2 ratios generally reproduced the observations when the CH 4 FixCoal simulation case was used. This implies that CH 4 from coal was a major contributor to the observed variations in the winter period ΔCH 4 /ΔCO 2 ratios. However, the model did not reproduce the observed ratio in 2012—this discrepancy requires further study. The trend of ΔCH 4 /ΔCO 2 was a slight decrease over time, which was attributed to the earlier onset of CH 4 emissions relative to fossil-fuel CO 2 , predominantly due to the reduction of CH 4 emissions from coal. In 2013, a relatively low tracer ratio was noted, which was caused by the large contribution of CO 2 from biomass burning. Overall, the observed AMY ΔCH 4 /ΔCO 2 ratios provide an efficient approach for validating the existing estimates of East Asian sectoral emissions of CH 4. • Synoptic scale variability (SSV) of CH 4 and CO 2 at Anmyeondo, South Korea was mainly caused by emission variations from eastern and northeastern China. • Simulated wintertime SSV of CH 4 a from coal was well matched with observations at Anmyeondo during 2010–2020. • EDGAR v6 China anthropogenic CH 4 /CO 2 emission ratio was overestimated against observation based SSV ΔCH 4 /ΔCO 2 mole fractions ratios. • Decline trend of wintertime SSV ΔCH 4 /ΔCO 2 mole fractions ratios Anmyeondo was attributed to a slower growth rate of China anthropogenic CH 4 emission compared to CO 2. • Observed low ΔCH 4 /ΔCO 2 ratio in 2013 was most likely caused by large contribution CO 2 from biomass burning. [ABSTRACT FROM AUTHOR]

Carbon monoxide (CO) is a key tracer of anthropogenic pollution, and it indirectly affects climate change. Anmyeon-do (AMY, 36.54° N, 126.33° E), a World Meteorological Organization/Global Atmosphere Watch Program (WMO/GAW) regional background station in Korea, provides continuous observations of CO mole fractions at the surface and vertical profiles within 0.5–9 km that are also collected by aircraft campaigns. The vertical profiles collected in 2019 were analyzed using meteorological parameters such as vertical velocity and boundary layer height (BLH), and a strong relationship was observed among them; however, the vertical distribution, which was influenced by unexpected strong pollution plumes, did not exhibit a strong relationship with vertical velocity and BLH. On November 16, we captured a strong CO signal within the boundary layer and at approximately 2 km above the BLH, where vertical profiles of the aerosol scattering coefficient at 550 nm were simultaneously observed with the same vertical structure. To identify the origins and source types of the stratification of the pollution plume for CO and aerosol, we also analyzed surface in situ observations of particle size distributions and reactive gases (NO x , O 3 , and SO 2) as well as the column averaged dry-air mole fraction of carbon monoxide (XCO) and measurements of aerosol optical depth obtained from the tropospheric monitoring instrument (TROPOMI) and moderate resolution imaging spectroradiometer (MODIS) satellite, respectively. The high CO event within the BLH, including observations at the surface site, was attributed to domestic burning sources. Convective uplifting of industrial fossil fuel emissions from eastern China was responsible for the high CO dry mole fraction in the low free troposphere (FT) and the elevated aerosol scattering coefficient. Statistical analyses of one-year surface in situ observations of CO reveal that CO-emission sources from eastern China contributed to extremely high CO spikes (≥80th percentile of CO or ≥ 350 ppb, approximately) in 2019. Therefore, we concluded that emissions from eastern China have a potentially leading role in the observed high pollution events at the surface and the lower FT over the AMY station in 2019. The increase in ground temperature, with the acceleration of the global warming process, can intensify the convective uplifting of pollution plumes from emission source regions to FT over East Asian regions. In addition, such an occurrence of the stratification of the atmospheric pollution plume in the troposphere should be considered in future studies on radiative forcing to improve air-quality forecasting in this region. • Collected vertical profiles of CO and aerosol scattering coefficient based on aircraft. • Estimated pollution stratification of CO and aerosol on the surface and free troposphere (FT). • Clarified regional transport of CO from source regions to troposphere over Korea. • East Asian continent deemed responsible for high CO pollution in surface and FT. [ABSTRACT FROM AUTHOR]

The lack of reference ground-based PM 2.5 observation leads to large gaps in air quality information, particularly in many areas of the developing world. This study investigated a new solution for urban air-quality monitoring in regions with limited reference ground-based monitoring. We developed an observation-based method by combining satellite remote-sensing techniques and a newly established low-cost sensor network to estimate long-term PM 2.5 concentrations over Krasnoyarsk, a highly industrialized Siberian city. First, a physical model was developed to estimate PM 2.5 concentrations using satellite remote-sensing with the aid of ground-based meteorological and radiosonde observations. Observations from the ground-based sensor network were then used to calibrate the deviations in the satellite-derived PM 2.5 concentrations. The results show that the satellite-based PM 2.5 concentrations obtained by our physical model were in good agreement with the sensor observations (R = 0.78 on the monthly scale). The deviation in satellite-derived annual PM 2.5 concentrations resulted from data restrictions that occurred at noon and data loss in winter were identified as 20% and 30%, respectively. The regional transport of smoke from forest wildfires increased PM 2.5 concentration to 150 μg/m3 in the summer 2018. The average PM 2.5 concentrations in the urban districts could reach 35 μg/m3, which far exceeded the World Health Organization air quality guideline. These results underscore the good ability of our new method to determine PM 2.5 concentrations in regions with limited reference ground-based monitoring. Use of sensor and meteorological observations greatly improved satellite detection of PM 2.5 concentration. In addition, our method has the potential for global application to improve determination of PM 2.5 concentrations, especially in sparsely monitored regions. • A physical model was developed to estimate PM 2.5 using satellite remote sensing. • Sensor observations were used to calibrate satellite-derived PM 2.5 concentrations. • Use of sensor and meteorological observations improved satellite detection of PM 2.5 • Transport of smoke from forest wildfires greatly increased PM 2.5 in summer 2018. • The method has the potential for worldwide use to determine global PM 2.5 [ABSTRACT FROM AUTHOR]