Comparative analysis of long-term (2005-2016) spatiotemporal variations in high-level tropospheric formaldehyde (HCHO) in Guangdong and Jiangsu Provinces in China

Abstract

High-level tropospheric formaldehyde (HCHO) columns were observed in Guangdong and Jiangsu Provinces in China by using the long-term records (2005-2016) of Aura OMI measurements. Given the socioeconomic status of Guangdong and Jiangsu Provinces, research concerning the widespread air pollution issues throughout these regions was imperative. Hence, the spatiotemporal variations in HCHO and the potential contributors were analyzed accordingly. We evaluated the spatiotemporal characteristics of HCHO columns in province- and prefecture-level cites to investigate the region of interest in various spatial resolutions. Hence, administrative shapefiles were used to clip the HCHO distributions to represent various sample regions. The spatial resolution of the OMI monthly gridded HCHO columns was 0.25° × 0.25°, but some ancillary data have finer resolutions than that of the level-3 gridded HCHO columns. Accordingly, the inverse distance-weighted interpolation algorithm and KD-Tree method were adopted for re-sampling fine spatial resolutions into 0.25° × 0.25°. The linear least square regression adopted in this study was the approach used to infer the potential trends exhibited in the HCHO images. The trends were fitted pixel by pixel, and the regional trends were calculated via zonal averaging of the administrative regions selected in the previously mentioned shapefiles. The Spearman correlation coefficients were employed to evaluate the similarity of the HCHO distribution and multitude sources (e.g., isoprene and anthropogenic VOCs). In Guangdong Province, HCHO columns concentrated in the Pearl River Delta (PRD), but an increasingly widespread distribution was observed in Jiangsu Province. An upward trend was found in both provinces from 2005 to 2010 that may be closely related to the rapid economy development in that period. Meanwhile, from 2011 to 2016, an overall downward trend was observed in these two regions, given the enacted multitude controls. With regard to seasonality, the highest HCHO columns were observed in spring and autumn, whereas the HCHO during summertime had the lowest concentration in Guangdong. The HCHO seasonal patterns corresponded to the seasonal patterns of sunlight intensity. Among all source sectors, industrial and transportation may contribute the most in the PRD, but all sectors may also contribute in the same order of magnitude in Jiangsu. In addition, biogenic sources may have a comparatively large contribution in the Northeastern Guangdong, and the biomass burning in summertime possibly played a substantial role in the summertime HCHO concentration in Jiangsu Province. Although isoprene plays significant role in HCHO concentration in global scale, the anthropogenic impact cannot be neglected as well. According to previous studies, anthropogenic sources have more than 40% influence. In addition, in comparison with isoprene, the Spearman correlation coefficients were high for anthropogenic VOCs with HCHO columns. Given the relatively large amount of emissions, industrial sources may be influential for more than 40%. Biomass burning sources cannot be ignored in woodlands, such as in Northeastern Guangdong. Transportation sources exhibited the most similar Spearman correlation coefficients in Guangdong, especially in PRD. Therefore, even a downward trend of transportation emissions was observed in PRD. They may account for a large amount of HCHO concentration. After a comparison, power-based emissions only took a small fraction of approximately 1% for Guangdong and Jiangsu.