Comparison of Aerosol Hygroscopcity, Volatility, and Chemical Composition between a Suburban Site in the Pearl River Delta Region and a Marine Site in Okinawa

Mingfu Cai,Shiro Hatakeyama,Fei Li,Hikari Yai,Chak K Chan,Atsushi Matsuki,Michihiro Mochida,Hanbing Xu,Yutaka Kondo,Haobo Tan,Yiming Qin,Kojiro Shimada,Jun Zhao,Liu Li,Misha I Schurman,Yange Deng

doi:10.4209/aaqr.2017.01.0020

Abstract

ABSTRACTA suite of advanced instruments were employed to measure aerosol hygroscopicity, volatility and chemical composition at a suburban site in the Pearl River Delta (PRD) Region and at a marine site in Okinawa, respectively. The results showed that the particle number concentration in PRD is approximately ten times higher than that in Okinawa. Organics contributes about one half of the total NR-PM1 concentration in PRD, while sulfate is the dominant component (about 60%) in Okinawa. Diurnal variation of the chemical species demonstrated that the site in PRD was affected by traffic-related sources and industrial emissions, while the one in Okinawa is mainly affected by regional emissions. The V-TDMA measurements showed that a large fraction (20–45%) of particles in Okinawa volatilized at about 200°C and nearly all particles volatilized at about 300°C, indicating that the particles were almost volatile in Okinawa. In contrast, a fraction (15–21%) of particles in PRD did not evaporate even when heated to about 300°C, implying that these particles might contain black carbon or low-volatile organics. For 40–200 nm particles in Okinawa, the hygroscopicity parameter κ is around 0.5, significantly higher than that of PRD particles (κ ≈ 0.26). Particles tend to have bimodal distribution in PRD and unimodal in Okinawa, indicating that the former is externally mixed while the latter is internally mixed.

Highlights

Atmospheric particles can affect the climate system directly by scattering and absorbing solar radiation, or indirectly by changing the cloud lifetime and albedo (Randall et al, 2007)
The fit based on the five modes in Guangzhou agree excellently with the measured particle number size distribution (PNSD), while the fit with the three modes in Cape Hedo is not as good as that in Aerosol Property Hygroscopicity (κ)
The Guangzhou site and the Cape Hedo site were used to study the aerosol properties in urban environment and marine environment, respectively

Summary

INTRODUCTION

Atmospheric particles can affect the climate system directly by scattering and absorbing solar radiation, or indirectly by changing the cloud lifetime and albedo (Randall et al, 2007). The physical and chemical properties of atmospheric particles can vary substantially at regional scales due to different emission sources and meteorological conditions. They are affected by transport that brings different air masses into the receptor area, potentially modifying aerosol properties in the region. The H/V-TDMA (Hygroscopicity and Volatility Tandem Differential Mobility Analyzer) and Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-ToFAMS) were employed to measure hygroscopicity, volatility, and chemical composition respectively. During the H-mode measurements, the selected particles of a specific diameter (D0) (from DMA1) were introduced into a Nafion humidifier (Model PD-70T-24ss, Perma Pure Inc., USA) to achieve 90% RH (Guangzhou) or 85%RH (Cape Hedo) equilibria. The hygroscopicity parameter κ was calculated according to κ-Köhler theory (Petters and Kreidenweis, 2007), based on the hygroscopicity growth factor (HGF), relative humidity (RH), and the properties of the aerosols: κ

RH exp

RESULTS AND DISCUSSION

CONCLUSION