Measurements of non-volatile aerosols with a VTDMA and their correlations with carbonaceous aerosols in Guangzhou, China

Heidi H Y Cheung,Hanbing Xu,Jian Z Yu,Chak K Chan,Haobo Tan,Fei Li,Cheng Wu

doi:10.5194/acp-16-8431-2016

Abstract

Abstract. Simultaneous measurements of aerosol volatility and carbonaceous matters were conducted at a suburban site in Guangzhou, China, in February and March 2014 using a volatility tandem differential mobility analyzer (VTDMA) and an organic carbon/elemental carbon (OC ∕ EC) analyzer. Low volatility (LV) particles, with a volatility shrink factor (VSF) at 300 °C exceeding 0.9, contributed 5 % of number concentrations of the 40 nm particles and 11–15 % of the 80–300 nm particles. They were composed of non-volatile material externally mixed with volatile material, and therefore did not evaporate significantly at 300 °C. Non-volatile material mixed internally with the volatile material was referred to as medium volatility (MV, 0.4 < VSF < 0.9) and high volatility (HV, VSF < 0.4) particles. The MV and HV particles contributed 57–71 % of number concentration for the particles between 40 and 300 nm in size. The average EC and OC concentrations measured by the OC ∕ EC analyzer were 3.4 ± 3.0 and 9.0 ± 6.0 µg m−3, respectively. Non-volatile OC evaporating at 475 °C or above, together with EC, contributed 67 % of the total carbon mass. In spite of the daily maximum and minimum, the diurnal variations in the volume fractions of the volatile material, HV, MV and LV residuals were less than 15 % for the 80–300 nm particles. Back trajectory analysis also suggests that over 90 % of the air masses influencing the sampling site were well aged as they were transported at low altitudes (below 1500 m) for over 40 h before arrival. Further comparison with the diurnal variations in the mass fractions of EC and the non-volatile OC in PM2.5 suggests that the non-volatile residuals may be related to both EC and non-volatile OC in the afternoon, during which the concentration of aged organics increased. A closure analysis of the total mass of LV and MV residuals and the mass of EC or the sum of EC and non-volatile OC was conducted. It suggests that non-volatile OC, in addition to EC, was one of the components of the non-volatile residuals measured by the VTDMA in this study.

Highlights

Carbonaceous aerosols comprising organic carbon (OC) and elemental carbon (EC) or black carbon (BC) are one of the major light absorption constituents and are abundant in particulate matter (PM) (Rosen et al, 1978; Hansen et al, 1984; Japar et al, 1986; Chow et al, 1993; Horvath, 1993; Liousse et al, 1993; Fuller et al, 1999; Putaud et al, 2010; Tao et al, 2014; Zhang et al, 2015)
As we only focus on Low volatility (LV) and medium volatility (MV), densities of 1.0 g cm−3 (Hitzenberger et al, 1999) and 1.5 g cm−3 are applied to VLV and VMV to obtain mass (m) concentrations of LV and MV residuals, respectively
Since volatility tandem differential mobility analyzer (VTDMA) data were not available during the new particle formation (NPF) event on 13 March 2014, we only focus on the NPF event on 20 February 2014 that happened after a cold front under a low PM2.5 concentration

Summary

Introduction

Carbonaceous aerosols comprising organic carbon (OC) and elemental carbon (EC) or black carbon (BC) are one of the major light absorption constituents and are abundant in particulate matter (PM) (Rosen et al, 1978; Hansen et al, 1984; Japar et al, 1986; Chow et al, 1993; Horvath, 1993; Liousse et al, 1993; Fuller et al, 1999; Putaud et al, 2010; Tao et al, 2014; Zhang et al, 2015). In China, the worsening of visibility degradation associated with PM has been of increasing concern in recent years. Numerous studies on air pollution were carried out in different cities in China including the Pearl River Delta (PRD) region, which is a fastdeveloping economic zone (Cheng et al, 2006; Wu et al, 2007; Andreae et al, 2008; Chan and Yao, 2008; Gnauk et al, 2008; Tan et al, 2013a). Cheung et al.: Measurements of non-volatile aerosols with a VTDMA tions of EC and OC measured at an urban Guangzhou (GZ) site were reported to vary from 6.8 to 9.4 and from 13.4 to 22.5 μg m−3, respectively (Yu et al, 2010)

Methods

Results

Conclusion