Abstract
In order to survey the seasonal variation of the chemical composition of particulate matter of 2.5 μm or less (PM 2.5 ), PM 2.5 was sampled from 8 February 2013 to 31 March 2014 in an industrial area of Chiba Prefecture, Japan. Chemical measurements of the sample included: ionic components (Na+, NH 4+ , Ca 2+ , Mg 2+ , K + , Cl - , NO 3- and SO₄ 2- ), carbonaceous components - organic carbon (OC) and elemental carbon (EC), and water-soluble organic carbon (WSOC). Also, secondary organic carbon (SOC) was measured based using the EC tracer method, and char-EC and soot-EC were calculated from the analytical results. The data obtained were interpreted in terms of temporal variation. Of the overall mean value of PM 2.5 mass concentration obtained during the study period, ionic components, OC and EC accounted for 45.3%, 19.7%, and 8.0%, respectively. NO 3- showed a unique seasonal distribution pattern due to a dependence on temperature and absolute humidity. It was estimated that an approximate temperature of 14℃ and absolute humidity of 7 g/m³ were critical for the reversible reaction of NH₄NO₃ (p) ≒ NH₃ (g)+HNO₃(g). The amount of OC and EC contributing to the monthly PM 2.5 mass concentration was higher in autumn and winter compared to spring and summer. This result could be attributed to the impact of burning biomass, since WSOC and the ratio of char-EC/soot-EC showed a similar pattern during the corresponding period. From the comparison of monthly WSOC/OC values, a maximum ratio of 83% was obtained in August (summer). The WSOC and estimated SOC levels derived from the EC tracer method correlated (R=0.77) in summer. The high occurrence of WSOC during summer was mainly due to the formation of SOC by photochemical reactions. Through long-term observation of PM 2.5 chemical components, we established that the degree to which the abovementioned factors influence PM 2.5 composition, fluctuates with seasonal changes.
Highlights
Over the last decade, significant evidence has proven that particulate matter, smaller than 2.5 μm, is hazardous to public health due to its ability to penetrate the thoracic cavity (Takebayashi et al, 2011; EPA, 2009; WHO, 2005)
This included validating the ionic balance of ionic components and comparing the sum of the measured chemicals with the measured PM2.5 mass concentrations to check for internal consistency
We defined the range of “total anions equivalent/total cation equivalent” as 0.8-1.2, in accordance with the provisional PM2.5 analytical procedure manual officially announced by Ministry of the Environment Japan (MOEJ) (MOEJ, 2007)
Summary
Significant evidence has proven that particulate matter, smaller than 2.5 μm, is hazardous to public health due to its ability to penetrate the thoracic cavity (Takebayashi et al, 2011; EPA, 2009; WHO, 2005). In Japan, environmental quality standards were enforced in September 2009. This standard states that the annual PM2.5 mass concentration is required to be less than, or equal to 15 μg /m3 and that the daily PM2.5 mass concentration should be less than or equal to 35 μg/m3. PM2.5 contains a multitude of source content. This contributes to the physical and chemical complexity that is still poorly characterised. As a result, drawing a link between PM2.5 emission sources, ambient mass concentrations and health effects becomes a complicated process. For a detailed understanding of the health risks associated with PM2.5 exposure, characterisation of their physical and chemical properties is required
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