Abstract
Wheat harvest and subsequent straw burning for maize planting can cause severe PM2.5 and PAH pollutions and deteriorate the air quality of nearby cities in consequence. PM2.5 samples were collected in Baoding urban area (BUA) from June 18 to July 7 of 2019, during and after wheat harvest (DWH and AWH, respectively). The “Migration Effect” (i.e., PM2.5 and PAHs transferred from rural to urban during DWH and AWH, respectively) was proved by both the later time for appearance of peak values of PM2.5 and PAHs and the air mass origins in BUA. The daily average PM2.5 (reported in µg m–3) 137 of DWH was 2.58 times 53.1 of AWH for BUA, regardless of its lower levels than the corresponding 156 and 75.6 for an adjacent rural site (ARS). The reverse trend was found for PAH mass contents (in µg g–1), AWH possessed much higher value of 139 than 27.8 of DWH, while no significant fluctuations occurred for PAH concentrations due to the varied PM2.5 levels. Four PAH sources including biomass burning (BB), coal combustion (CC), vehicle exhaust (VE) and industrial emissions (IN) were identified using positive matrix factorization (PMF). BB was the biggest contributor during whole sampling period (WSP), followed by CC, VE, and IN. BB increased from 17.3% to 37.1% along with the transition from DWH to AWH, indicated the impact of straw burning for maize planting. High share of CC suggested that coal was still an important civil fuel. The strict emission reduction measures made the industry smallest contributor in BUA. Lower VE share in BUA than ARS demonstrated that influence of high-intensity operation of wheat harvesters and rotary cultivators.
Highlights
Environmental contamination has occurred along with the process of industrialization and urbanization in the past few decades in China
BTH is an important wheat producing base in China and its air quality can be deteriorated by PM2.5 and polycyclic aromatic hydrocarbons (PAHs) associating with the activities of wheat harvest and subsequent straw burning for maize planting
Our previous study investigated the impact of wheat harvest associated behaviors on PM2.5 and PAHs for adjacent rural site (ARS) within Baoding city, which indicated the wheat harvest associated fugitive dust dramatically elevated the PM2.5 levels in DWH and PAHs levels were markedly promoted by straw burning in AWH
Summary
As a class of persistent organic pollutants (POPs), polycyclic aromatic hydrocarbons (PAHs) are widely found in the environmental mediums and always origin from incomplete incineration of coal, crop straws, garbage and the other organic substances (Xing et al, 2016; Han et al, 2019; Li et al, 2020b). Previous studies reported that biomass burning, domestic coal combustion, and coke production contributed 59%, 23%, and 15% to the total PAHs, respectively in China (Zhang et al, 2019a). The evaluation of impact of wheat harvest and subsequent straw burning for maize planting on PAHs of urban area is important to the improvement of urban air quality. The main purposes of this study were to: 1) analyze the changes of PM2.5 and PAHs in BUA associated with wheat harvest and subsequent straw burning activities; 2) to analyze the origins of air masses using backward trajectory clustering; and 3) identify the sources of PAHs using Positive Matrix Factor (PMF) model
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