Comment on acp-2021-1030

doi:10.5194/acp-2021-1030-rc2

Abstract

Abstract. Coarse particulate matter (i.e. PM with an aerodynamic diameter between 2.5 and 10âÂµm â PM2.5 and PM10 â or PMcoarse) has been increasingly recognized for its importance in PM10 regulation because of its growing proportion in PM10 and the accumulative evidence for its adverse health impact. In this work, we present comprehensive PMcoarse speciation results obtained through a 1-year-long (January 2020âFebruary 2021) joint PM10 and PM2.5 chemical speciation study in Hong Kong, a coastal and highly urbanized city in southern China. The annual average concentration of PMcoarse is 14.9âÂ±â8.6âÂµgâmâ3 (Â±âstandard deviation), accounting for 45â% of PM10 (32.9âÂ±â18.5âÂµgâmâ3). The measured chemical components explain â¼75â% of the PMcoarse mass. The unexplained part is contributed by unmeasured geological components and residue liquid water content, supported through analyses by positive matrix factorization (PMF) and the thermodynamic equilibrium model ISORROPIA II. The PMcoarse mass is apportioned to four sources resolved by PMF, namely soil dust/industrial and coal combustion, construction dust/copper-rich emissions, fresh sea salt, and an aged sea salt factor containing secondary inorganic aerosols (mostly nitrate). The PMcoarse concentration and source composition exhibit a distinct seasonal variation, a result mainly driven by the source areas the air masses have travelled through as revealed by back-trajectory analysis. In summer when the site is dominated by marine air mass, PMcoarse is the lowest (averageâ=â8.1âÂµgâmâ3) and sea salt the largest contributor (47â%), followed by the two dust factors (36â% in total). In winter when the site receives air mass mainly from the northern continental region, PMcoarse concentration triples (24.8âÂµgâmâ3), with the two dust factors contributing three quarters of the aerosol mass. The potential dust source areas are mapped using the concentration-weighted trajectory technique, showing either the Greater Bay Area or the greater part of southern China as the origin of fugitive dust emissions leading to elevated ambient PMcoarse loadings in Hong Kong. This study, the first of this kind in our region, provides highly relevant guidance for other locations with similar monitoring needs. Additionally, the study findings point to the need for further research on the sources, transport, aerosol processes, and health effects of PMcoarse.

Highlights

Coarse particulate matter (PMcoarse), defined as PM with aerodynamic diameter of 2.5–10 μm in the World Health Organization’s air quality guidelines, play important roles in air quality, public health, and global climate
The difference is consistent with combustion and secondary aerosol formation processes being the major sources of fine particles, whereas coarse particles are primarily generated by mechanical processes
The results show 435 that ~70 % of the unidentified mass is associated with the two dust factors, while the rest is residue liquid water content as implied from thermodynamic modeling using ISORROPIA II

Summary

Introduction

Coarse particulate matter (PMcoarse), defined as PM with aerodynamic diameter of 2.5–10 μm in the World Health Organization’s air quality guidelines, play important roles in air quality, public health, and global climate. Previous PMcoarse studies in Hong Kong were focused on suburban coastal area (Cohen et al, 2004), roadside environment (Cheng et al, 2015), and public transport micro-environments (Jiang et al, 2017). These studies provide limited representation of the general PMcoarse pollution characteristics given the predisposition to the influence by nearby sources; for example, sea 65 spray in coastal environment or traffic-related emissions in roadside environment. With the robust source apportionment analysis, we found that fugitive dust associated with regional influence is the dominant contributor of high PMcoarse loading in Hong Kong. The methodology and results from this study can serve to provide guidance to other locations with similar monitoring needs

Methods

Results

Conclusion