Abstract
Abstract. Black carbon (BC) is a dominant absorber in the visible spectrum and a potent factor in climatic effects. Vertical profiles of BC were measured using a micro-aethalometer attached to a tethered balloon during the Vertical Observations of trace Gases and Aerosols (VOGA) field campaign, in summer 2014 at a semirural site in the North China Plain (NCP). The diurnal cycle of BC vertical distributions following the evolution of the mixing layer (ML) was investigated for the first time in the NCP region. Statistical parameters including identified mixing height (Hm) and average BC mass concentrations within the ML (Cm) and in the free troposphere (Cf) were obtained for a selected dataset of 67 vertical profiles. Hm was usually lower than 0.2 km in the early morning and rapidly rose thereafter due to strengthened turbulence. The maximum height of the ML was reached in the late afternoon. The top of a full developed ML exceeded 1 km on sunny days in summer, while it stayed much lower on cloudy days. The sunset triggered the collapse of the ML, and a stable nocturnal boundary layer (NBL) gradually formed. Accordingly, the highest level Cm was found in the early morning and the lowest was found in the afternoon. In the daytime, BC was almost uniformly distributed within the ML and significantly decreased above the ML. During the field campaign, Cm averaged about 5.16 ± 2.49 µg m−3, with a range of 1.12 to 14.49 µg m−3, comparable with observational results in many polluted urban areas such as Milan in Italy and Shanghai in China. As evening approached, BC gradually built up near the surface and exponentially declined with height. In contrast to the large variability found both in Hm and Cm, Cf stayed relatively unaffected through the day. Cf was less than 10 % of the ground level under clean conditions, while it amounted to half of the ground level in some polluted cases. In situ measurements of BC vertical profiles would hopefully have an important implication for accurately estimating direct radiative forcing by BC and improving the retrieval of aerosol optical properties by remote sensing in this region.
Highlights
Black carbon (BC), produced from incomplete combustion processes, is a strongly absorbing constituent of atmospheric aerosols (Moosmüller et al, 2009; Bond et al, 2013)
We present results from in situ measurements of BC vertical profiles using a lightweight and small-sized (117 mm × 66 mm × 38 mm) microaethalometer
A further examination on BC emissions (0.25◦ × 0.25◦) from four sectors in 2012 in the North China Plain (NCP) region was performed on the basis of emission data generated from the multi-resolution emission inventory for China (MEIC, http://www.meicmodel.org) model (Li et al, 2015), which is developed by a technologybased approach (Lei et al, 2011)
Summary
Black carbon (BC), produced from incomplete combustion processes, is a strongly absorbing constituent of atmospheric aerosols (Moosmüller et al, 2009; Bond et al, 2013). As a major absorber in the visible spectrum, BC heats the atmosphere and largely counterbalances cooling effects of scattering aerosols on climate (Jacobson, 2001; Ramanathan et al, 2005; Stier et al, 2007). Another reason for BC to be of public concern is that inhaled BC poses a huge threat to human health (Janssen et al, 2012; Nichols, 2013). Two BC polluted layers found at about 4.5 and 8 km altitudes were reported by Babu et al (2011b) Indirect methods such as recently proposed lidar remote sensing might be able to conduct continuous measurements (Miffre et al, 2015). The diurnal cycle of BC vertical distributions was explored for the first time in the NCP region
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