Emission characteristics, sources, and airborne fate of speciated organics in particulate matters in a Hong Kong residence.

A growing number of studies warn of the adverse health effects of indoor particulate matters (PM). However, little is known about the molecular compositions and emission characteristics of PM-bound organics (OM) indoors, a critical group of species with highest concentration and complexity in indoor PM. In a Hong Kong residence where prescribed activities were performed with normal frequency and intensity, we found that the activities significantly elevated not only the total concentration but also the fraction of OM in indoor PM. However, the concentration of the total PM-bound OM outdoors (10.3 ± 0.7 µg/m3 ) surpassed that for the indoor counterpart during the undisturbed period (8.2 ± 0.1 µg/m3 ), that is, period when there was no activity with high emission of PM but the residual effects of previous activities might remain. Emissions of indoor activities involving combustion or high-temperature processes significantly elevated the indoor-to-outdoor (I/O) ratios for a majority of organic species. In addition, gas-to-particle partitioning, secondary formation, carrying-over (residues of pollutants in the air), and re-emission also modulated the I/O ratios of some compounds. Chemically comprehensive emission profiles of speciated organics were obtained for 5 indoor activities in the residence. While the indoor contribution to PM-bound OM was estimated to be not higher than 13.1% during the undisturbed period, carrying-over and/or re-emission seemed to exist for certain compounds emitted from cigarette smoking and incense burning. This study enhances knowledge on emissions and airborne fate of speciated organics in indoor PM.

Real-time molecular characterization of air pollutants in a Hong Kong residence: Implication of indoor source emissions and heterogeneous chemistry.

Due to the high health risks associated with indoor air pollutants and long-term exposure, indoor air quality has received increasing attention. In this study, we put emphasis on the molecular composition, source emissions, and chemical aging of air pollutants in a residence with designed activities mimicking ordinary Hong Kong homes. More than 150 air pollutants were detected at molecular level, 87 of which were quantified at a time resolution of not less than 1 hour. The indoor-to-outdoor ratios were higher than 1 for most of the primary air pollutants, due to emissions of indoor activities and indoor backgrounds (especially for aldehydes). In contrast, many secondary air pollutants exhibited higher concentrations in outdoor air. Painting ranked first in aldehyde emissions, which also caused great enhancement of aromatics. Incense burning had the highest emissions of particle-phase organics, with vanillic acid and syringic acid as markers. The other noteworthy fingerprints enabled by online measurements included linoleic acid, cholesterol, and oleic acid for cooking, 2,5-dimethylfuran, stigmasterol, iso-/anteiso-alkanes, and fructose isomers for smoking, C28 -C34 even n-alkanes for candle burning, and monoterpenes for the use of air freshener, cleaning agents, and camphor oil. We showed clear evidence of chemical aging of cooking emissions, giving a hint of indoor heterogeneous chemistry. This study highlights the value of organic molecules measured at high time resolutions in enhancing our knowledge on indoor air quality.

Continuous effectiveness of replacing catalytic converters on liquified petroleum gas-fueled vehicles in Hong Kong.

To mitigate the concentrations of air pollutants in the atmosphere, an intervention program of replacing the converters of liquefied petroleum gas (LPG) fueled vehicles was implemented by the Hong Kong government between October 2013 and April 2014. Data of ambient volatile organic compounds (VOCs) and other trace gases continuously monitored from September 2012 to April 2017 at a roadside site were used to evaluate the continuous effectiveness of the replaced catalytic converters on the reduction of air pollutants. The measurement data showed that LPG-related VOCs (propane and n/i-butanes) and several trace gases (CO, NO and NO2) decreased significantly from before to after the program (p < 0.01). To further assess the efficiency of the program, five periods covering before the program, during the program, 1st year after the program, 2nd year after the program and 3rd year after the program were categorized. The values of propane and n/i-butanes decreased from Period-1 (before the program) to Period-2 (during the program), and from Period-2 to Periods 3-5 (after the program) (p < 0.01). In addition, the reduction rates of propane and n/i-butanes remained high and constant in Periods 3-5, suggesting that either had the vehicle owners themselves routinely replaced the converters at suitable interval afterwards, or were their vehicles caught by a remote sensing program checking excessive emissions. Source apportionment analysis indicated that LPG-fueled vehicular emissions were the top contributor to ambient VOCs in the roadside environment while the VOCs emitted from LPG-fueled vehicles indeed decreased at a rate of 4.21 ±â€¯2.38 ppbv/year (average ±â€¯95% confidence interval) from Period-1 to Period-5 (p < 0.01). Furthermore, the photochemical box model simulations revealed that the net negative contribution of VOCs and NOx emitted from LPG-fueled vehicles to O3 production strengthened at a rate of 1.9 × 10-2 pptv/day from Period-1 to Period-5 (p < 0.01). The findings proved the continuous effectiveness of the intervention program, and are of help to future control strategies in Hong Kong.