Black carbon aerosol and its radiative impact at a high‐altitude remote site on the southeastern Tibet Plateau

Abstract

Aerosol black carbon (BC) was measured with an Aethalometer™ at Lulang, a high‐altitude station in southeastern Tibetan Plateau (TP), from July 2008 to August 2009. Daily mean BC loadings varied from 57.7 to 5368.9 ng m−3 (grand average ± standard deviation = 496.5 ± 521.2 ng m−3), indicating a significant BC burden even at free tropospheric altitudes. BC loadings were highest during the premonsoon and lowest during the monsoon, and peaks in BC were coincident with high atmospheric boundary layers. Daily peaks in BC occurred from 08:00 to 10:00 local time with minor fluctuations at other times. The BC mass absorption efficiency (MAE) was calculated from elemental carbon concentrations obtained from a thermal/optical reflectance method and absorption coefficients from the Aethalometer™, and values ranged from 6.1 to 31.7 m2 g−1 (average = 16.6 ± 5.7 m2 g−1). Strong variations in the MAEs during the monsoon can be ascribed to large uncertainties due to low BC and babs and possibly coatings on the BC. High MAEs during premonsoon pollution events were likely due to internal mixing during transport. The mean direct surface radiative forcing (DRF) estimated from a radiation model was −19.9 (±7.4) W m−2 for the full aerosol population and −3.9 (±1.8) W m−2 for a BC only scenario. The BC DRF during a case study (−36.0 W m−2) was much stronger than the typical, and the BC contribution to the forcing was higher (~50%) than usual (~20%). These results show that BC can at times account for a relatively large fraction of the aerosol surface heating over the southeast TP, which may affect both climate and hydrological cycles.

Sources and physicochemical characteristics of black carbon aerosol from the southeastern Tibetan Plateau: internal mixing enhances light absorption

“…An intensive measurement campaign was conducted from Figure 1. Black carbon concentrations (µg m −3 ) measured at 15 sampling sites in the Himalayas and on the Tibetan Plateau based on the measurements from this study (blue solid circles) and other studies (black solid circles) from Ma et al (2003), Pant et al (2006), Marinoni et al (2010), Stone et al (2010), Babu et al (2011), Engling et al (2011, Li et al (2017), Wan et al (2015), Wang et al (2015a), M. Wang et al (2016), Zhu et al (2016), and Raatikainen et al (2017). More detailed information concerning these studies is summarized in Table S1.…”

“…However, several recent studies showed that the impact of internal Tibetan sources (e.g., yak dung combustion by local residents) on the atmosphere of the TP should not be overlooked (Chen et al, 2015;Li et al, 2016a;. In the past few decades, a number of field campaigns conducted on the TP have investigated the concentrations, sources, and spatial and temporal variations of BC aerosol (e.g., Engling et al, 2011;Cong et al, 2015;Zhu et al, 2016;Wang et al, 2017;. Recently, research has begun to focus on the light absorption characteristics of BC particles in the atmosphere and snow (Li et al, 2016b, c;.…”

“…Although some aerosol-related field studies have been conducted on the TP, the BC measurements were mainly made using online or offline filter-based techniques (e.g., aethalometer, thermal/optical reflectance method, and multiangle absorption photometer) (e.g., Engling et al, 2011;Marinoni et al, 2010;Wan et al, 2015;Zhu et al, 2016;Li et al, 2017). These techniques are based on the bulk particle deposition onto the filters, and they cannot provide high time resolution information on of BC size and mixing state.…”

High Contribution of Secondary Brown Carbon to Aerosol Light Absorption in the Southeastern Margin of Tibetan Plateau

“…There is growing concern that glaciers on the TP are in retreat, due in part to the influence of atmospheric black carbon (BC) and dust which are light‐absorbing materials (William et al, ). The optical properties and radiative effects of these two substances have been well documented over the past decades (e.g., Qu et al, ; Wang, Cao, Han, Tian, Zhang, et al, ; Wang, Cao, Han, Tian, Zhu, et al, ; Zhang et al, ; Zhao, Wang, et al, ). More recently, a group of colored organic compounds, collectively known as brown carbon (BrC), has been found to absorb sunlight, especially at short wavelengths (Andreae & Gelencsér, ).…”

Response to Referee #1

“…An intensive measurement campaign was conducted from Figure 1. Black carbon concentrations (µg m −3 ) measured at 15 sampling sites in the Himalayas and on the Tibetan Plateau based on the measurements from this study (blue solid circles) and other studies (black solid circles) from Ma et al (2003), Pant et al (2006), Marinoni et al (2010), Stone et al (2010), Babu et al (2011), Engling et al (2011), Zhao et al (2012), Li et al (2017), Wan et al (2015), Wang et al (2015a), M. Wang et al (2016), Zhu et al (2016), and Raatikainen et al (2017). More detailed information concerning these studies is summarized in Table S1.…”