Characteristics of submicron particulate matter at the urban roadside in downtown Hong Kong—Overview of 4 months of continuous high‐resolution aerosol mass spectrometer measurements

Abstract

Hong Kong, one of the world's most densely populated cities and an international financial center, has been suffering from traffic-related air pollution. This study presents the first real-time high-resolution aerosol mass spectrometry measurements of submicron nonrefractory particulate matter (NR-PM 1 ) at the urban roadside in Hong Kong from March to July 2013 with the aim to identify major sources, to assess local and nonlocal emissions, and to characterize trends at different time scales. Organics were dominant, with fresh primary organic aerosol representing two thirds of the total measured organics. Cooking contributions in organic aerosol were assessed directly for the first time in Hong Kong and exceeded those related to vehicles although traffic was still the major PM 1 source when elemental carbon was included. These findings were supported by additional measurements including traffic data, elemental/organic carbon, and VOC data. Springtime concentrations were about double of those in summer, due to a strong seasonal transition which affected meteorological conditions and street-level circulation. Local formation of secondary species was not clearly discernible in either season. The elemental composition of organic aerosol remained stable with similar elemental ratios across the covered seasons: OM/OC: 1.49 ± 0.13, O/C: 0.25 ± 0.10, H/C: 1.68 ± 0.08 for spring and OM/OC: 1.43 ± 0.14, O/C: 0.21 ± 0.11, H/C: 1.69 ± 0.08 for summer. Diurnal changes in H/C and O/C as a result of mixing of primary organic aerosol and secondary organic aerosol were evident in the van Krevelen plot.

Formation of secondary organic aerosols from gas-phase emissions of heated cooking oils

“…The POA mass spectra between different cooking oils exhibited strong correlations (R 2 > 0.97) and agreed well with the ambient COA factor obtained at roadside sites in the commercial and shopping area of Mongkok in Hong Kong (Lee et al, 2015). The SOA mass spectra between different cooking oils displayed good correlations (R 2 > 0.94), suggesting a high degree of similarity.…”

“…Cooking-related organic aerosol (COA), thought to be primary in origin, contributed 10-34.6 % of the total OA in urban areas (Allan et al, 2010;Sun et al, 2011Sun et al, , 2012Ge et al, 2012;Mohr et al, 2012;Crippa et al, 2013;Lee et al, 2015). Lee et al (2015) found that COA even dominated the contribution to POA at roadside sites in the commercial and shopping area of Mongkok in Hong Kong.…”

“…The correlation coefficients (R 2 ) between POA and SOA unit mass resolution (UMR) spectra of heated oil and COA resolved by positive matrix factorization (PMF) analysis (Lee et al, 2015) were calculated and summarized in Table 2 to evaluate their similarities. The POA mass spectra between different cooking oils exhibited strong correlations (R 2 > 0.97) and agreed well with the ambient COA factor obtained at roadside sites in the commercial and shopping area of Mongkok in Hong Kong (Lee et al, 2015).…”

“…Lee et al (2015) found that COA even dominated the contribution to POA at roadside sites in the commercial and shopping area of Mongkok in Hong Kong. Cooking may be a large source of SOA in urban areas, yet the formation of SOA from cooking remains poorly understood.…”

Dominant contribution of oxygenated organic aerosol to haze particles from real-time observation in Singapore during an Indonesian wildfire event in 2015

“…Additionally, locally emitted cooking OA (COA), which has been shown to have similar mass spectra to BBOA (Lee et al, 2015;Liu et al, 2017), could also contribute to BBOA during the P2 period. This observation of the average concentrations and contributions of OA factors indicate that (1) fossil fuel combustion was likely the main source of HOA at most of the observation period, and (2) Indonesian wildfires contributed to the elevated BBOA, PBOA and OOA concentrations during the P1 period.…”