Development of an Automated System (PPWD/PILS) for Studying PM2.5 Water-Soluble Ions and Precursor Gases: Field Measurements in Two Cities, Taiwan

Abstract

An automated system consisting of a particle-into-liquid sampler (PILS) and a parallel plate wet denuder (PPWD) coupled with an ion chromatography was used for simultaneous measurement of ambient water-soluble ions in PM 2.5 and precursor gases. The performance of the PPWD/PILS was validated by comparing it with the PDS (porous metal denuder sampler) for precursor gases (NH 3 , HONO, HNO 3 and SO 2 ) and PM 2.5 ionic species (NH 4 + , NO 3 -, SO 4 2-, Na + , Cl -and K + ) measured in Taipei and Hsinchu Cities of Taiwan. Good correlations were demonstrated with linear regression slopes ranging from 0.92 to 1.04 and 0.84 to 0.97 as well as R 2 ranging from 0.76 to 0.83 and 0.89 to 0.94, for precursor gases and PM 2.5 ions, respectively. The accuracy of the current system for precursor gases outperforms the other commercial systems. Field continuous data showed that NH 3 was the most abundant precursor gas with the diurnal pattern peaking at low nocturnal boundary heights and during rush hours with local traffic emissions in Taipei, and with the pattern peaking only at mid-day associated with regional sources in Hsinchu. A reverse diurnal pattern for HONO in Taipei reflected the daytime photolysis and its nocturnal heterogeneous reaction, while its concentration was relatively constant at very low level in Hsinchu. SO 4 2-, NH 4 + and NO 3 -exhibited very similar diurnal patterns with the mean concentrations of 4.56 ± 3.14, 1.55 ± 1.16 and 0.52 ± 0.5 µg m -3 in Taipei, and 7.95 ± 5.52, 2.41 ± 1.95 and 0.96 ± 1.10 µg m -3 in Hsinchu, respectively. Correspondingly high concentrations of major ions to precursor gases were associated with the photochemical secondary aerosol formations and heavy traffic in Taipei. Based on an ammonia-rich atmosphere and high SOR values, (NH 4 ) 2 SO 4 and NH 4 NO 3 were inferred to be the dominant inorganic salts in PM 2.5 at both sites, which were also verified by the ion balance analysis.

Characterization of Atmospheric PM2.5 Inorganic Aerosols Using the Semi-Continuous PPWD-PILS-IC System and the ISORROPIA-II

“…The field comparison results of the PPWD-PILS-IC with the PDS for some major WSI species (Na + , K + , NH 4 + , Cl − , NO 3 − , and SO 4 2− ) are shown in Figure 4. It is found that the linear regression slopes and coefficient (R 2 ) of the determination range from 0.99 to 1.17 and from 0.88 to 0.98, respectively, which are better than those (slope 0.75-0.97 and R 2 0.77-0.94) in Li et al [31]. For K + , Na + , and NH 4 + , the improvement is even more obvious with higher R 2 of 0.89, 0.92, and 0.93, respectively (R 2 = 0.77, 0.77, and 0.89, respectively in the previous study) implying good stability of the monitoring system and the manual sampler.…”

“…In comparison, the PPWD/PILS consisting of PPWD [36,37] and PILS [38,39] and coupled with the IC (i.e., PPWD-PILS-IC) developed by our group [31] showed good agreement with the PDS for precursor gases (slope 0.92-.04) and PM 2.5 ion species as well (slope 0.75-0.97 and R 2 : 0.77-0.94). In addition, the PPWD-PILS-IC system has low MDLs (method detection limit) which are less than 0.01 µg/m 3 for Na + , Ca 2+ , NO 2 − , and SO 4 2− and 0.02 µg/m 3 for NH 4 + , NO 3 − , and Cl − , respectively.…”

“…The hourly data of the monitoring system was converted to the 24-h average data for comparison with the PDS data. The PPWD-PILS-IC monitoring system was presented in detail in Li et al [31] and is described briefly below. A 16.7 L/min EPA PM 10 inlet [54] and a PM 2.5 VSCC inlet (very sharp cut cyclone) were used to remove particles larger than 2.5 µm in aerodynamic diameter.…”

“…Nevertheless, this method can be time-consuming and labor-intensive and is not fast enough to characterize the rapid evolution of atmospheric particles. Currently, there are some hourly monitoring systems for water-soluble ions in PM 2.5 including the wet-annular denuder and steam-jet aerosol collector (WAD/SJAC) [27], the monitor for aerosols and gases in ambient air (MARGA) [28], the gas particle ion chromatography system (GPIC) [29], the ambient ion monitor ion chromatograph (AIM-IC) [30], and the parallel plate wet denuder and particle into liquid sampler) (PPWD/PILS) [31]. Some previous studies have shown that the WAD/SJAC measured NH 4…”

Overview of the Special Issue "PM2.5 in Asia" for 2015 Asian Aerosol Conference

“…The average concentration of chemical components showed that local air pollution also influenced air quality in Kumamoto. For simultaneous measurement of ambient water-soluble ions in PM 2.5 and precursor gases, Li et al (2017) developed an automated system consisting of a particle-into-liquid sampler (PILS) and a parallel plate wet denuder (PPWD) coupled with an ion chromatography. The performance of the PPWD/PILS was validated by comparing it with the PDS (porous metal denuder sampler) and the accuracy of the system for precursor gases was found to outperform the other commercial systems.…”