[1] This study was part of the international field measurement Campaigns of Air Quality Research in Beijing and Surrounding Region 2006 (CAREBeijing-2006). We investigated a new particle formation event in a highly polluted air mass at a regional site south of the megacity Beijing and its impact on the abundance and properties of cloud condensation nuclei (CCN). During the 1-month observation, particle nucleation followed by significant particle growth on a regional scale was observed frequently (~30%), and we chose 23 August 2006 as a representative case study. Secondary aerosol mass was produced continuously, with sulfate, ammonium, and organics as major components. The aerosol mass growth rate was on average 19 μg m -3 h -1 during the late hours of the day. This growth rate was observed several times during the 1-month intensive measurements. The nucleation mode grew very quickly into the size range of CCN, and the CCN size distribution was dominated by the growing nucleation mode (up to 80% of the total CCN number concentration) and not as usual by the accumulation mode. At water vapor supersaturations of 0.07-0.86%, the CCN number concentrations reached maximum values of 4000-19,000 cm -3 only 6-14 h after the nucleation event. During particle formation and growth, the effective hygroscopicity parameter κ increased from about 0.1-0.3 to 0.35-0.5 for particles with diameters of 40-90 nm, but it remained nearly constant at ~0.45 for particles with diameters of ~190 nm. This result is consistent with aerosol chemical composition data, showing a pronounced increase of sulfate.

Rapid aerosol particle growth and increase of cloud condensation nucleus activity by secondary aerosol formation and condensation: A case study for regional air pollution in northeastern China

Reconstructing 1-km-resolution high-quality PM2.5 data records from 2000 to 2018 in China: spatiotemporal variations and policy implications

. Fine particulate matter with aerodynamic diameters ≤2.5 µ m
(PM 2.5 ) has adverse effects on human health and the atmospheric
environment. The estimation of surface PM 2.5 concentrations has made
intensive use of satellite-derived aerosol products. However, it has been a great challenge to obtain high-quality and high-resolution PM 2.5 data from both ground and satellite observations, which is essential to monitor air pollution over small-scale areas such as metropolitan regions. Here, the space–time
extremely randomized trees (STET) model was enhanced by integrating updated
spatiotemporal information and additional auxiliary data to improve the
spatial resolution and overall accuracy of PM 2.5 estimates across
China. To this end, the newly released Moderate Resolution Imaging
Spectroradiometer Multi-Angle Implementation of Atmospheric Correction AOD product, along with meteorological, topographical and land-use data and
pollution emissions, was input to the STET model, and daily 1 km PM 2.5 
maps for 2018 covering mainland China were produced. The STET model performed
well, with a high out-of-sample (out-of-station) cross-validation coefficient
of determination ( R2 ) of 0.89 (0.88), a low root-mean-square error of
10.33 (10.93)  µ g m −3 , a small mean absolute error of 6.69 (7.15)  µ g m −3 and a small mean relative error of 21.28 % (23.69 %).
In particular, the model captured well the PM 2.5 concentrations at both
regional and individual site scales. The North China Plain, the Sichuan
Basin and Xinjiang Province always featured high PM 2.5 pollution
levels, especially in winter. The STET model outperformed most models
presented in previous related studies, with a strong predictive power (e.g.,
monthly R2=0.80 ), which can be used to estimate historical
PM 2.5 records. More importantly, this study provides a new approach
for obtaining high-resolution and high-quality PM 2.5 dataset across mainland
China (i.e., ChinaHighPM 2.5 ), important for air pollution studies
focused on urban areas.

/pdf/improved-1-km-resolution-pm-2-5-estimates-across-china-using-2guh8bqr18.pdf

Improved 1 km resolution PM 2.5 estimates across China using enhanced space–time extremely randomized trees

Influence of meteorological conditions on PM2.5 concentrations across China: A review of methodology and mechanism.

MODIS Collection 6.1 aerosol optical depth products over land and ocean: validation and comparison

Air quality is concerned with pollutants in both the gas phase and solid or liquid phases. The latter are referred to as aerosols, which are multifaceted agents affecting air quality, weather and climate through many mechanisms. Unlike gas pollutants, aerosols interact strongly with meteorological variables with the strongest interactions taking place in the planetary boundary layer (PBL). The PBL hosting the bulk of aerosols in the lower atmosphere is affected by aerosol radiative effects. Both aerosol scattering and absorption reduce the amount of solar radiation reaching the ground and thus reduce the sensible heat fluxes that drive the diurnal evolution of the PBL. Moreover, aerosols can increase atmospheric stability by inducing a temperature inversion as a result of both scattering and absorption of solar radiation, which suppresses dispersion of pollutants and leads to further increases in aerosol concentration in the lower PBL. Such positive feedback is especially strong during severe pollution events. Knowledge of the PBL is thus crucial for understanding the interactions between air pollution and meteorology. A key question is how the diurnal evolution of the PBL interacts with aerosols, especially in vertical directions, and affects air quality. We review the major advances in aerosol measurements, PBL processes and their interactions with each other through complex feedback mechanisms, and highlight the priorities for future studies.

/pdf/aerosol-and-boundary-layer-interactions-and-impact-on-air-4u0ggedy1h.pdf

Huiwen Xue

Papers

Aerosol and boundary-layer interactions and impact on air quality