北京城市、郊区和区域背景点一次高臭氧事件中挥发性有机物和光化学活性对颗粒物的影响

Impact of volatile organiccompounds and photochemical activities on particulate matters during a high ozoneepisode at urban, suburb and regional background stations in Beijing

 PingShao ^a, Xiaobin Xu ^b, Xiaoling Zhang ^a,c,d,*,Jing Xu ^c, Ying Wang ^b, Zhiqiang Ma ^c,e

^a PlateauAtmosphere and Environment Key Laboratory of Sichuan Province, School ofAtmospheric Sciences, Chengdu University of Information Technology, Chengdu, 610225,PR China

^bChinese Academy of Meteorological Sciences, Beijing, 100081, PR China

^cInstitute of Urban Meteorology, Chinese Meteorological Administration, Beijing,100089, PR China

^dShanghai Key Laboratory of Meteorology and Health, Shanghai, 200030, PR China

^eEnvironmental Meteorology Forecast Center of Beijing-Tianjin-Hebei, Beijing, 100089,PR China

摘要：

挥发性有机物（VOCs）在颗粒物（PM）和氧化剂的形成中扮演着关键作用，因此增强了夏季的空气污染。通过对2011年6月多个外场观测（城市点：海淀，HD；郊区点：昌平，CP；区域背景点：上店子，SDZ）数据的分析，我们发现在观测期间平均O₃浓度排序为：SDZ> CP > HD。平均PM浓度排序为：HD> CP > SDZ。HD总VOCs的平均浓度与CP相近，但是远远高于SDZ。三个站点的含氧挥发性有机物（OVOCs）占据了VOCs的最大比例（~40%），之后是烷烃和烯烃。白天（07:00-18:00LT）在高温（HD和CP：>30℃；SDZ:> 28 ℃）和低湿（RH< 60%）条件下PM的浓度和O_x（=O₃+NO₂）有好的正相关关系。但是，在低温（HD和CP：<26 ℃；SDZ：<22 ℃）和高湿（RH> 80%）条件下PM的浓度和O_x有部分的负相关关系。在高温和低湿条件下PM的浓度要么与芳香烃正相关（HD和CP）要么负相关（SDZ）。三个站点气团的老化程度排序为：SDZ> CP > HD。这个可以定性解释不同的PM-芳香烃关系。我们的数据显示在湿润条件下除非PM浓度高于140μgm^-3，VOCs的其他种类可能会促进PM浓度的增加。这项研究证实了VOCs对于北京夏季PM和氧化剂形成的重要性。

Abstract：

Volatileorganic compounds (VOCs) play key roles in the formation of particulate matter(PM) and oxidants and hence enhance the summertime air pollution. With dataanalysis from various field observations (urban station: Haidian, HD; suburbstation: Changping, CP; regional background station: Shangdianzi, SDZ) in June2011, we found that the mean O3 concentrations throughout the observationperiod can be arranged in order: SDZ＞CP＞HD.The mean PM concentrations can be arranged in order: HD＞CP＞SDZ.The mean concentration of total VOCs at HD was close to that at CP, but muchhigher than that at SDZ. Oxygenated volatile organic compounds (OVOCs) made thelargest portion of VOCs (~40%) at the three stations, followed by alkanes andalkenes. Good positive correlations between the concentrations of PM and O_x(=O₃+NO₂)at high air temperature (>30 ℃ at HD and CP; > 28 ℃ at SDZ) and low RH (<60%) were found in the daytime (07:00–18:00 LT). However, the PM concentrationswere partly negatively correlated with Ox at lower temperatures (< 26 ℃ atHD and CP; < 22 ℃ at SDZ) and higher RH (>80%).The PM concentrations were found either positively (HD and CP) or negatively (SDZ)correlated with aromatics at high temperature and low RH. The aging degree ofair masses at the three stations can be arranged in order: SDZ＞CP＞HD.This can qualitatively explain the different PM-aromatics correlations. Ourdata suggested the other groups of VOCs may promote the increase of PMconcentrations unless the PM levels become higher than 140 μgm^-3under humid conditions. This study confirms the importance of VOCs in theformation of summertime PM and oxidants over Beijing.

关键词：颗粒物（PM）挥发性有机物（VOCs）臭氧污染事件北京

Keyword:Particulate matter (PM); Volatile organic compounds (VOCs); Ozone episode; Beijing

亮点：

1、  PM和O₃平行的光化学形成造成正的PM-O_x关系

2、  HD和CP观察到正的PM-芳香烃关系，但是在SDZ是负的

3、  在高臭氧污染事件中OVOCs占据了VOCs的最大比例（~40%）

4、  在湿润条件下VOCs可能会促进夏季PM浓度的增加

Highlights

• Parallelphotochemical formations of PM and O3 caused positive PM-Ox correlations.

• PositivePM-aromatics correlations were found at HD and CP, but negative at SDZ.

• OVOCsmade the largest portion of VOCs (~40%) in the high ozone episode.

• VOCsmay promote the increase of summertime PM concentrations under humidconditions.

Fig. 1. Map showing the study sitesand topography in Beijing and surrounding regions. Haidian (HD), Changping(CP), and Shangdianzi sites (SDZ) represent downtown Beijing, Beijing suburband regional background sites in the Beijing-Tianjin-Hebei region, respectively.

Fig. 2. Time series of airpollutants and meteorological factors during the observation period at Haidian(HD, top left panel), Changping (CP, top right panel), and Shangdianzi sites(SDZ, bottom panel). The gray areas indicate the period when VOCs were sampledsynchronously.

Fig. 3. Scatterplots of PM vs. Oxconcentrations under different temperature (T) and relative humidity (RH)conditions at Haidian (HD), Changping (CP) and Shangdianzi (SDZ).

Fig. 4. Scatterplots and normalizedkernel density of PM1/PM2.5 vs. Ox under different temperature (T) and relativehumidity (RH) conditions at Changping (CP) and Shangdianzi (SDZ).

Fig. 5. Scatterplots of PM vs.aromatics under different relative humidity (RH), temperature (T) and Oxconcentration at Haidian (HD), Changping (CP) and Shangdianzi (SDZ).

Fig. 6. Scatterplots of toluene tobenzene and m,p-xylene to ethylbenzene at Haidian (HD), Changping (CP) andShangdianzi (SDZ).

Fig. 7. Variations of alkanes,alkenes, halohydrocarbon and OVOCs as a function of PM concentrations (20 μgm-3 increment) at Haidian (HD), Changping (CP) and Shangdianzi (SDZ) (thesquares in the boxes are mean values; the lines in the boxes are median values;the upper and lower boundaries of the boxes indicate 75th and 25th percentiles;the whiskers above and below the boxes indicate maximums and minimums).