Heterogeneous ice nucleating particle (INP) concentrations are reported for a site on the eastern margin of Beijing, China, during the period 4 May to 4 June 2018. INP concentrations were measured continuously at −20, −25, and −30 °C in a repeating cycle by a newly developed, automated continuous flow diffusion chamber, and reached concentrations as high as 2800 sL−1 during dust‐impacted periods. Study average concentrations were 70 ± 70, 230 ± 290, and 430 ± 500 sL−1 at −20, −25, and −30 °C. There was no clear relationship between pollution periods, identified based on fine‐mode particle concentration increases, and INP concentrations or characteristics. Other anthropogenic emissions, such as non‐combustion industrial or agricultural activities play an unresolved role.
Abstract. Open biomass burning (OBB) has significant impacts on air pollution, climate change and potential human health. OBB has gathered wide attention but with little focus on the annual variation of pollutant emission. Central and eastern China (CEC) is one of the most polluted regions in China. This study aims to provide a state-of-theart estimation of the pollutant emissions from OBB in CEC from 2003 to 2015, by adopting the satellite observation dataset -the burned area product (MCD64Al) and the active fire product (MCD14 ML) -along with local biomass data (updated biomass loading data and high-resolution vegetation data) and local emission factors. The successful adoption of the double satellite dataset for long-term estimation of pollutants from OBB with a high spatial resolution can support the assessing of OBB on regional air quality, especially for harvest periods or dry seasons. It is also useful to evaluate the effects of annual OBB management policies in different regions. Here, monthly emissions of pollutants were estimated and allocated into a 1 × 1 km spatial grid for four types of OBB including grassland, shrubland, forest and cropland.
Abstract. Most previous modeling studies about black carbon (BC) transport and its
impact over the Tibetan Plateau (TP) conducted simulations with horizontal
resolutions coarser than 20 km that may not be able to resolve the
complex topography of the Himalayas well. In this study, the two experiments
covering all of the Himalayas with the Weather Research and Forecasting model
coupled with Chemistry (WRF-Chem) at the horizontal resolution of 4 km but
with two different topography datasets (4 km complex topography and 20 km
smooth topography) are conducted for pre-monsoon season (April 2016) to
investigate the impacts of topography on modeling the transport and
distribution of BC over the TP. Both experiments show the evident accumulation
of aerosols near the southern Himalayas during the pre-monsoon season,
consistent with the satellite retrievals. The observed episode of high
surface BC concentration at the station near Mt. Everest due to heavy
biomass burning near the southern Himalayas is well captured by the
simulations. The simulations indicate that the prevailing upflow across the
Himalayas driven by the large-scale westerly and small-scale southerly
circulations during the daytime is the dominant transport mechanism of southern
Asian BC into the TP, and it is much stronger than that during the nighttime.
The simulation with the 4 km topography resolves more valleys and mountain
ridges and shows that the BC transport across the Himalayas can overcome the
majority of mountain ridges, but the valley transport is more efficient. The
complex topography results in stronger overall cross-Himalayan transport
during the simulation period primarily due to the strengthened efficiency of
near-surface meridional transport towards the TP, enhanced wind speed at
some valleys and deeper valley channels associated with larger transported
BC mass volume. This results in 50 % higher transport flux of BC across
the Himalayas and 30 %–50 % stronger BC radiative heating in the atmosphere
up to 10 km over the TP from the simulation with the 4 km complex topography
than that with the 20 km smoother topography. The different topography also
leads to different distributions of snow cover and BC forcing in snow. This
study implies that the relatively smooth topography used by the models with
resolutions coarser than 20 km may introduce significant negative biases in
estimating light-absorbing aerosol radiative forcing over the TP during the
pre-monsoon season.
Highlights.
The black carbon (BC) transport across the Himalayas can overcome the
majority of mountain ridges, but the valley transport is much more efficient
during the pre-monsoon season. The complex topography results in stronger overall cross-Himalayan
transport during the study period primarily due to the strengthened
efficiency of near-surface meridional transport towards the TP, enhanced
wind speed at some valleys and deeper valley channels associated with
larger transported BC mass volume. The complex topography generates 50 % higher transport flux of BC
across the Himalayas and 30 %–50 % stronger BC radiative heating in the
atmosphere up to 10 km over the Tibetan Plateau (TP) than the
smoother topography, which implies that the smooth topography used by the
models with relatively coarse resolution may introduce significant negative
biases in estimating BC radiative forcing over the TP during the pre-monsoon
season. The different topography also leads to different distributions of snow
cover and BC forcing in snow over the TP.
The size-resolved properties of atmospheric
black carbon (BC) importantly
determine its absorption capacity and cloud condensation nuclei (CCN)
ability. This study reports comprehensive vertical profiles of BC
size-related properties over the Beijing area (BJ) and Continental
Europe (CE). BC mass loadings over CE were in the range of clean background
over BJ. For both planetary boundary layer (PBL) and lower free troposphere,
the BC mass median core diameter over BJ during the cold season was
0.21 ± 0.02 μm, larger than the warm season over BJ and
CE (0.18 ± 0.01 μm), which may reflect seasonal differences
in emissions. The BC coatings were positively correlated with the
pollution level, with background BC having a smaller coated count
median diameter (0.19 ± 0.01 μm). The modeled absorption
enhancement (E
abs) due to coatings was
1.23 ± 0.14 for the background but in the PBL following a linear
expression (E
abs = 0.13 × MassBC,surface + 1.26). The CCN ability of BC was significantly
enhanced in the polluted PBL, due to both enlarged size and increased
hygroscopicity. In polluted BJ at predicted supersaturations, ∼0.08%
half of the BC number could be activated, whereas the cleaner environment
needs ∼0.14%. The results here suggest that the highly coated
and absorbing BC can be efficiently incorporated into clouds and can
exert important indirect radiative impacts over the polluted East
Asia region.
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