Aircraft measurements of black carbon in the boundary layer over the North China Plain

Abstract

Black carbon aerosol (BC) is the principle absorber to modify the shortwave radiative balance between the lower atmosphere and the surface in polluted environment, which was in-situ characterized by aircraft measurements using a single particle soot photometer (DMT inc., SP2) throughout the boundary layer up to 3km over the North China Plain around Beijing megacity. The flights were conducted in both hot season (late 5 spring, Apr. -Jun. 2012, surface temperature >20°C, 10 flights) and cold season (winter, Dec. 2016, surface temperature <5°C, 6 flights). The BC mass in the daytime well-developed planetary boundary layer (BCPBL) was found to be largely influenced by meteorology which modulated the local emission and regional transport. The BCPBL in hot season showed no apparent vertical gradient or correlation with the PBL height (PBLH); whereas in winter the BCPBL decreased at higher altitude and accumulated towards the surface due 10 to reduced horizontal wind speed at low level, and was anti-correlated with the PBLH. The more homogenous vertical mixing of BCPBL in hot season may result from the stronger convective mixing due to higher surface temperature, in addition the predominant southerly wind may have advected the largely polluted air mass, offsetting its dilution effect; whereas in winter the predominant cleaner air mass from the north had important dilution effect on local emissions. The overall averages showed lower BC mass loading 15 in the surface layer during hot season but similar loadings (3.5-4 µg m -3 ) in the PBL for both seasons. The highly turbulent air conditions, as frequently observed in the early afternoon during hot season, largely diluted the BC mass down to the background level (~0.5 µg m -3 ); whereas in winter the BCPBL was significantly elevated under dynamic air condition due to efficient transport of polluted air mass from the south. 20The BCPBL in winter showed systematically larger core size (mass median diameter, MMD=217±4nm) than in late spring (209±7nm), which may be due to a higher contribution from the residential emission sector in cold season. The high BC mass loadings were mostly associated with a high fraction of thick coatings (Fcoating), and the higher air moisture enhanced the coating content of BCPBL. These suggest the primary sources with a range of co-emitted species significantly contributed to the coatings of BC, and the secondary 25 formation which could be enhanced by elevated RH also played important role. The BC after significant removal showed much lower Fcoating (~0.06) and smaller core size (MMD ~193nm), implying that the coated and larger BC particle was preferentially removed. The scavenging efficiency of BC in the entrainment zone (EZ) showed positive correlation with the change of coatings between PBL and EZ for both seasons (Fcoating,PBL > Fcoating,EZ), however showed seasonally different behaviors in terms of core size 30 (MMDPBL>MMDEZ in late spring, but the opposite in winter). These results provide the basis to evaluate the BC direct radi...

Simulated impacts of vertical distributions of black carbon aerosol on meteorology and PM&lt;sub&gt;2.5&lt;/sub&gt; concentrations in Beijing during severe haze events

“…The IPR analysis has been widely applied to illustrate the impacts of each physical/chemical process on the variations in O3 concentrations (Zhang and Rao, 1999;Jiang et al, 2012;Gao et al, 2017;Gao et al, 2018). The improved IPR analysis method developed by Chen et al (2019) in WRF-Chem model is used in this work to https://doi.org/10.5194/acp-2021-611 Preprint.…”

“…quantitatively analyze the contributions of physical/chemical processes to PM2.5 concentrations, including the contributions from the sub-grid convection (CONV), vertical mixing (VMIX), chemistry (CHEM), regional transport (TRA), wet scavenging (WET), emission source (EMI) and other processes (OTHER). CONV refers to the transport within the sub-grid wet convective updrafts (Chen et al, 2019) and VMIX is affected by atmospheric turbulence and vertical distribution of PM2.5 concentrations (Zhang and Rao, 1999;Gao et al, 2018). CHEM represents PM2.5 production and loss including gas-phase, cloud and aerosol chemistry.…”

“…BC can influence concentrations of PM2.5 during haze events because of its impact on PBL and other meteorological fields (Gao et al, 2016b;Wilcox et al, 2016;Qiu et al, 2017;Gao et al, 2018;Wang et al, 2019;Chen et al, 2021). Gao et al (2016b) used the WRF-Chem model to simulate the haze event that occurred in the NCP in January 2010 and found a maximum increase in PM2.5 of 14.4 μg m -3 (5.1%) due to the DRE of BC.…”

“…CC BY 4.0 License. (SP2) (Zhao et al, 2018;Tian et al, 2019;Zhao et al, 2019;. During the period of severe pollution from to 19 December 2016, Zhao et al (2019) collected BC vertical profiles over Beijing by Air350 aircraft and found that the vertical profiles can be classified into two types.…”

The Observation Path Problems and the Formation Conditions of the Elevated Layer of Black Carbon Aerosol

“…The observation platforms mainly include iron towers, tethered balloons, unmanned aircrafts, and manned aircrafts. In recent years, researchers have conducted detection studies in multiple locations around the world using tethered balloons [10][11][12][13][14]1], unmanned aircraft [15], and manned aircraft [16][17][18][19][20][21][22][23]5]. Some of the detections have had global or continental coverage, for example, in the Arctic, Europe, North America, the tropical North Atlantic [5], the Pacific Ocean from 80N to 67S [18,24], the Arctic [16], and western and northern Europe [19]; some of the detections have focused on regional areas of a country, such as two cities in southern India [20], four cities in New Zealand [10], the largest city in the Yarlung Zangbo Valley [21], valleys in Italy [11], Beijing in…”