Measurement report: Long-term changes in black carbon and aerosol optical properties from 2012 to 2020 in Beijing, China

Atmospheric aerosols play an important role in the radiation balance of the earth–atmosphere system. However, our knowledge of the long-term changes in equivalent black carbon (eBC) and aerosol optical properties in China is very limited. Here we analyze the 9-year measurements of eBC and aerosol optical properties from 2012 to 2020 in Beijing, China. Our results showed large reductions in eBC by 71 % from 6.25 ± 5.73 µg m−3 in 2012 to 1.80 ± 1.54 µg m−3 in 2020 and 47 % decreases in the light extinction coefficient (bext, λ = 630 nm) of fine particles due to the Clean Air Action Plan that was implemented in 2013. The seasonal and diurnal variations of eBC illustrated the most significant reductions in the fall and at nighttime, respectively. ΔeBC / ΔCO also showed an annual decrease from ∼ 7 to 4 ng m−3 ppbv−1 and presented strong seasonal variations with high values in spring and fall, indicating that primary emissions in Beijing have changed significantly. As a response to the Clean Air Action Plan, single-scattering albedo (SSA) showed a considerable increase from 0.79 ± 0.11 to 0.88 ± 0.06, and mass extinction efficiency (MEE) increased from 3.2 to 3.8 m2 g−1. These results highlight the increasing importance of scattering aerosols in radiative forcing and a future challenge in visibility improvement due to enhanced MEE. Brown carbon (BrC) showed similar changes and seasonal variations to eBC during 2018–2020. However, we found a large increase of secondary BrC in the total BrC in most seasons, particularly in summer with the contribution up to 50 %, demonstrating an enhanced role of secondary formation in BrC in recent years. The long-term changes in eBC and BrC have also affected the radiative forcing effect. The direct radiative forcing (ΔFR) of BC decreased by 67 % from +3.36 W m−2 in 2012 to +1.09 W m−2 in 2020, and that of BrC decreased from +0.30 to +0.17 W m−2 during 2018–2020. Such changes might have important implications for affecting aerosol–boundary layer interactions and the improvement of future air quality.

Pseudomonas Tumuqiensis Sp. Nov., Isolated From Greenhouse Soil

A Gram-stain-negative, aerobic, rod-shaped and motile bacterium, named LAMW06T, was isolated from greenhouse soil in Beijing, China. In the 16S rRNA gene sequence comparison, strain LAMW06T had the highest similarity with Pseudomonas cuatrocienegasensis 1NT was 97.4%. Phylogenetic analysis base on the 16S rRNA and three housekeeping gene sequences (gyrB, rpoB and rpoD) indicated that LAMW06T represented a member of the genus Pseudomonas. The genome sequence size of the isolate was 5.5 Mb, with the DNA G+C content of 63.5 mol%. The average nucleotide identity and DNA–DNA hybridization values between strain LAMW06T and closely related members of Pseudomonas borbori R-20821T, Pseudomonas taeanensis MS-3T and Pseudomonas cuatrocienegasensis 1NT were 90.9%, 82.4%, 81.5 % and 43.0%, 25.9%, 24.6 % respectively. The major fatty acids contained summed feature 3 (C16:1 ω6c and/or C16:1 ω7c), C18:1 ω7c and C16:0. The primary respiratory quinone was ubiquinone-9. The main polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, six aminophospholipids, six phospholipids, one aminolipid and one glycolipid. According to the genotypic, phylogenetic and chemotaxonomic data, strain LAMW06T represents a novel species within the genus Pseudomonas, for which the name Pseudomonas tumuqiensis sp. nov. is proposed. The type strain is LAMW06T (=GDMCC 1.2003T =KCTC 72829T).