Spatial–temporal variations, sources, and transport of airborne inhalable metals (PM<sub>10</sub>) in urban and rural areas of northern China

Abstract

<p><strong>Abstract.</strong> Atmospheric particle pollution is a serious environmental issue in China, especially the northern regions. Ambient air loadings (ng m<sup>−3</sup>), pollution sources and apportionment, and transport pathways of trace (Cd, Co, Cu, Ni, Pb, V, and Zn) and major (Al, Ca, Fe, and Mg) metals associated with inhalable particulate matters (PM<sub>10</sub> aerosols) were characterized in urban, rural village, and rural field areas of seven cities (from inland in the west to the coast in the east: Wuwei, Yinchuan, Taiyuan, Beijing, Dezhou, Yantai, and Dalian) across northern China by taking one 72 h sample each site within a month for a whole year (April 2010 to March 2011). Ambient PM<sub>10</sub> pollution in northern China is especially significant in the cold season (October–March) due to the combustion of coal for heating and dust storms in the winter and spring. Owing to variations in emission intensity and meteorological conditions, there is a trend of decrease in PM<sub>10</sub> levels in cities from west to east. Both air PM<sub>10</sub> and the associated metal loadings for urban and rural areas were comparable, showing that the current pattern of regional pollution in China differs from the decreasing urban–rural-background transect that is usual in other parts of the world. The average metal levels are Zn (276 ng m<sup>−3</sup>) ≫ Pb (93.7) ≫ Cu (54.9) ≫ Ni (9.37) > V (8.34) ≫ Cd (2.84) > Co (1.76). Judging from concentrations (mg kg<sup>−1</sup>), enrichment factors (EFs), a multivariate statistical analysis (principal component analysis, PCA), and a receptor model (absolute principal component scores-multiple linear regression analysis, APCS-MLR), the airborne trace metals (Zn, Pb, Cu, and Cd) in northern China were mainly anthropogenic, and mostly attributable to coal combustion and vehicle emissions with additional industrial sources. However, the Co was mostly of crustal origin, and the V and Ni were mainly from soil/dust in the western region and mostly from the petrochemical industry/oil combustion in the east. The accumulation of typical "urban metals" (Pb, Zn, Cd, and Cu) showed a trend of increase from west to east, indicating their higher anthropogenic contribution in eastern cities. The winter northwestern monsoon and westerly jet stream were the dominant forces in the long-range transport of airborne PM metals in northern China, with potentially global implications.</p>

Source identification and apportionment of heavy metals in urban soil profiles

“…In fact, coal for electricity generation and for domestic cooking and heating accounts for approximately 70% of the China national energy budget, thereby large amounts of HMs are emitted due to the ''concentrating effect'' while burning. Supported by such type of findings (Luo et al, 2014), it could be concluded that, after the phase-out of leaded gasoline from 1997, the principal anthropogenic source for both airborne and soil Pb in mainland China is coal combustion rather than vehicle exhaust.…”

“…For further source apportionment of HMs in different soil layers, the receptor model APCS-MLR (Luo et al, 2014) was then used to estimate the contributions (%) of various anthropogenic sources for each metal. The APCS method enabled categories of the major pollution sources to be identified along with the quantitative contributions of each source to pollutant species (Thurston et al, 2011).…”

“…The HM contaminants in urban soils often originate from multiple sources (Wong et al, 2006), including natural (pedogenic processes) and various anthropogenic sources (atmospheric deposition of industrial and vehicle emissions, and direct input by human activities). Therefore, serving directed pollution control, it is crucial to discriminate pollution sources, that has become a significant environmental issue (Hu and Cheng, 2013;Szolnoki et al, 2013;Luo et al, 2014). Furthermore, besides spatial http://dx.doi.org/10.1016/j.chemosphere.2015.01.048 0045-6535/Ó 2015 Elsevier Ltd. All rights reserved.…”

“…Compared with atmospheric research (Belis et al, 2013;Luo et al, 2014), it was extremely limited by the effective methods available. Currently, the source studies about soil pollution are mainly source identification, including the enrichment factors (EFs) classifying natural and anthropogenic origins (Ye et al, 2011), multivariate analyses (principal component analysis, PCA; cluster analysis, CA) for grouping natural and key anthropogenic input types (Zhang, 2006;Davis et al, 2009) and associate with geostatistics for large scale investigations (Nanos and Rodríguez Martín, 2012;Sun et al, 2013), and using stable isotopic signatures such as 206 Pb/ 207 Pb and 208 Pb/ 207 Pb to distinguish specific Pb contributors (Cloquet et al, 2006;Luo et al, 2011).…”

“…But for the aerosol study (Li et al, 2013;Nguyen et al, 2013), many approaches have been applied to both identify and apportion pollution sources, including receptor models such as Chemical Mass Balance (CMB) model, PCA related methods (Absolute Principal Component Scores, APCS; Multiple Linear Regression, PCA-MLR; UNMIX model), and Positive Matrix Factorization (PMF). Recently, APCS-MLR was also developed to estimate the source contribution of airborne particulate HMs (Luo et al, 2014). Nonetheless, such methods for assessing soil HM pollution are still absent.…”