Analysis on scavenging effect of precipitation processes on PM2.5 in different cities of Sichuan Basin

doi:10.11755/j.issn.1006-7639(2023)-04-0620

Abstract

Abstract:

Studying the impact of precipitation on PM_2.5 mass concentration in different regions can provide an important scientific support for the air quality assessment and forecast as well as pollution prevention in this region. Based on the hourly precipitation observation data and PM_2.5 mass concentration monitoring data in five typical cities (Chengdu, Leshan, Yibin, Mianyang and Dazhou) of Sichuan Basin from 2016 to 2021, the scavenging effect of precipitation processes on PM_2.5 was analyzed in different cities from some aspects including the occurrence time, duration, intensity of precipitation and the initial mass concentration of PM_2.5. The results show that the proportion of positive scavenging processes of precipitation on PM_2.5 increases with the increase of precipitation intensity or initial mass concentration of PM_2.5 in Sichuan Basin, and the scavenging rate rises. Under the condition of air pollution, the scavenging effect of precipitation with intensity exceeding 1 mm·h^-1 on PM_2.5 improves obviously in Sichuan Basin, and the scavenging rate reaches 35.0%. The scavenging effect is positively correlated with the duration of precipitation processes, and the scavenging rate of precipitation processes with the duration more than 3 hours is 9.0%-18.0% higher than that of precipitation processes with the duration less than or equal to 3 hours. The probability of positive scavenging processes is higher in the early morning and afternoon in Sichuan Basin, and the precipitation processes in the early morning have better scavenging effect on PM_2.5. In comparison, the proportion of positive scavenging processes is higher in Leshan and Yibin after the precipitation, and under different initial mass concentrations of PM_2.5, the scavenging rate is significantly higher than that in other cities with the increase of precipitation duration.

Key words: PM_2.5, precipitation process, scavenging rate, air quality

摘要：

探究降水对不同区域PM_2.5质量浓度的影响，可为当地空气质量评估和预报以及大气污染防治等提供重要科学支撑。利用2016—2021年四川盆地成都、乐山、宜宾、绵阳和达州5个典型城市逐小时降水观测资料和PM_2.5质量浓度监测数据，从降水过程发生时段、持续时间、强度以及降水前PM_2.5初始浓度等方面，探析降水过程对不同区域城市PM_2.5的清除作用。结果表明：随着降水强度或PM_2.5初始质量浓度增加，四川盆地PM_2.5正清除过程占比增加，清除率升高。空气污染状态下，1 mm·h^-1及以上降水强度对四川盆地PM_2.5清除作用明显提升，清除率达35.0%。PM_2.5清除作用与降水过程持续时间呈正相关，降水持续时间超过3 h的清除率较持续时间小于等于3 h的高出9.0%~18.0%。四川盆地凌晨和下午的降水过程出现正清除的概率较高，且凌晨的降水过程对PM_2.5清除效果更好。对比来看，降水发生后，乐山和宜宾出现正清除过程占比较高，且在不同PM_2.5初始质量浓度下，随着降水持续时间增加，清除率明显高于其他地区。

关键词: PM_2.5, 降水过程, 清除率, 空气质量

CLC Number:

LIN Dan, GUO Xiaomei, WANG Weijia. Analysis on scavenging effect of precipitation processes on PM_2.5 in different cities of Sichuan Basin[J]. Journal of Arid Meteorology, 2023, 41(4): 620-628.

林丹, 郭晓梅, 王维佳. 四川盆地不同区域城市降水过程对PM_2.5清除作用分析[J]. 干旱气象, 2023, 41(4): 620-628.

Figures/Tables 9

Fig.1 The monthly variations of mean mass concentration of PM2.5 and precipitation in Sichuan Basin during 2016-2021

Fig.2 The diurnal variation of mean mass concentration of PM2.5 （a） and mean precipitation （b） in representative cities of different regions of Sichuan Basin during 2016-2021

Fig.3 The proportion of positive scavenging processes under different air qualities in representative cities of different regions of Sichuan Basin during 2016-2021

Fig.4 The relation of scavenging rate of rainfall processes with different precipitation intensities under different initial mass concentrations of PM2.5 in representative cities of different regions of Sichuan Basin during 2016-2021 （a） initial mass concentration of PM2.5 between 35 and 75 μg·m-3，（b） initial mass concentration of PM2.5 higher than 75 μg·m-3

Tab.1

降水强度/（mm·h^-1）	成都	达州	乐山	绵阳	宜宾
<1	49.5	55.8	57.6	52.7	54.7
1~4	58.9	69.6	70.8	56.5	71.4
>4	58.1	72.6	81.5	63.5	88.6

Tab.2

降水强度/（mm·h^-1）	正清除个例	正清除率				负清除个例	负清除率
降水强度/（mm·h^-1）	正清除个例	0~<10	10~<30	30~<50	≥50	负清除个例	>-10~0	>-30~-10	>-50~-30	≤-50
<1	3 386	33.9	42.5	16.6	6.9	2 882	40.2	39.5	11.2	9.1
1~4	702	16.5	39.6	25.2	18.7	365	31.9	40.2	14.8	13.1
>4	226	12.4	30.2	23.1	34.2	78	39.2	43.1	13.7	3.9

Tab.3

城市	负清除过程						正清除过程
	优		良		污染		优		良		污染
	≤3 h	>3 h	≤3 h	>3 h	≤3 h	>3 h	≤3 h	>3 h	≤3 h	>3 h	≤3 h	>3 h
成都	-21.4	-30.5	-13.4	-16.0	-7.2	-9.0	21.5	25.3	16.3	24.7	11.5	26.1
达州	-23.5	-23.5	-16.3	-14.3	-9.8	-18.6	18.1	25.4	16.7	31.6	12.6	29.6
乐山	-25.1	-31.3	-13.4	-12.5	-4.8	—	19.9	33.2	19.2	33.6	17.5	39.7
绵阳	-22.8	-32.5	-12.1	-13.0	-6.2	-7.8	17.6	25.9	13.4	25.0	12.6	24.3
宜宾	-24.8	-24.5	-12.6	-11.6	-9.2	-6.5	20.1	31.6	18.0	35.8	14.6	36.5
盆地	-23.5	-28.5	-13.6	-13.5	-7.4	-10.5	19.4	28.3	16.7	30.1	13.7	31.2

Fig.5 The proportion of precipitation processes in each interval in representative cities of different regions of Sichuan Basin during 2016-2021

Fig.6 The proportion of the positive and negative scavenging processes in each interval in representative cities of different regions of Sichuan Basin during 2016-2021

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