• API (Air Pollution Index) Data for PM10 Mass Concentrations Analysis

Adapted from Choi et al. 2008

The weekend effect in climate variables and air pollutants have been found, but it is still equivocal whether the occurrence of the weekend effect is attributed to boundary-layer anthropogenic aerosol processes or semi-weekly synoptic weather system. This study investigates the weekend effect in PM10 mass concentrations, and its relationship with synoptic-scale weather variability (850hPa geopotential height) in Beijing and Tianjin. The two cities are geographically close, very likely being influenced by the same weather system. Both cities have large industrial complexes that emit large amount of air pollutants. We used the anomaly values from the weekly means and took FFT to extract 7-day frequency and amplitude of the anomalies and its random orders. As results, both cities have a peak of spectrum nearby 0.14 day -1 in summers. Correlations between the normalized variances of surface PM10 concentration and geopotential height are low, implying that anthropogenic causes more likely influence the weekend effects in Beijing and Tianjin.

Detailed Characteristics of Weekend Effects in Chi-nese Cities Yong-Sang Choi1, and Bo-Ram Kim1

1Department of Environmental Science and Engineering, Ewha Womans University, Seoul 120-750 Korea

EGU2011-678

• The weekly change in PM10 (aerosol particulate matter with a diameter < 10 m) concentrations for the high-PM10 stations clearly reveals high and low values for weekdays and weekends, re-spectively (Fig. 1).

Introduction

Data

① The API is defined as the highest in-dex among the sub-indices of three leading pollutants: PM10, SO2, andNO2.

② The sub-indices-IPM10, ISO2, and INO2

-are

the values converted from the ob-served mass concentrations (C) in µg m-3 of the leading pollutants (Table 1).

•http://www.sepa.gov.cn/quality/air.php3•http://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.html• Google Earth• Choi, Y.-S., C.-H. Ho, D. Chen, Y.-H. Noh, and C.-K. Song (2008), Spectral analysis of weekly variation in PM10 mass concentration and environment conditions over China, Atmospheric Environment, 42, 655–666.• Ho, C.-H., Y.-S. Choi, and S.-K. Hur (2009), Long-term changes in summer weekend ef-fect over northeastern China and the connection with regional warming, Geophysical Research Letters, 36, L15706, doi:10.1029/2009GL039509.• Gong, D.-Y., D. Guo, and C.-H. Ho (2006), Weekend effect in diurnal temperature range in China: Opposite signals between winter and summer, J. Geophys. Res., 111, D18113, doi:10.1029/2006JD007068.

Reference

③ PM10-polluted days and clean days are used.④ A continuous dataset of daily aerosol concentrations for spectral analysis is

available for the period from Jun, 5, 2000 to Aug, 30, 2009.⑤ Winter season (DJF) was excluded from the analysis due to the large amount of

missing data.• Two Big Cities in China, Beijing and Tianjin, for Analysis

Adapted from Choi et al. 2008

① Beijing and Tianjin are big cities in China with 135 km distance.② Tianjin (Beijing) is categorized as a city with a high (moderate) normalized

weekly variance.(Table 2)③ Beijing is situated on a valley, Tianjin is situated near a coast.④ Both cities are characterized with monsoon-influenced climate according to

Köppen climate classification.• NCEP/NCAR Reanalysis I for Pressure Level Analysis

① Geopotential height dataset for 17 pressure level and 28 sigma levels.② Spatial resolutions of 2.5° ＊ 2.5°.③ Beijing and Tianjin is located in a same grid of the data.

Methods and Experimental Design• Fast Fourier Transform (FFT)

① The discrete Fourier transform, X, of the time series by using the fast Fourier transform (FFT) algorithm.

② The periodogram for a finite time series was then calculated as the squared magnitude of X:

• Weekend effect has seasonality (Gong et al., 2006) and long-term change in its phase (Ho et al., 2009) → Operating FFT separately for each

season and year.

③ The periodogram indicates the strength of the signal with respect to frequency.

④ Artificial cyclic data with noise may change the peak frequency of the periodogram (Fig. 2)

Strength of Frequency of PM10 Concentra-tions

• PM10 concentrations have sea-sonal cycle and long-term trend. → The row values converted to the mass concentration anomalies from the 7-day mean (Fig. 3).

• Beijing

• Tianjin

• More focus on JJA, 2002

Strength of Frequency of GPH850

Weekend Effect of PM10 and the Relation with GPH850

R2 MAM JJA SON

Beijing 0.0375 0.0794 0.0784

Tianjin 0.049 0.494 0.0514

• R2 : Coefficient of determination between normalized variances of 850 hPa geopoten-tial height and PM10 concentrations

• Normalized variance( ) is de-

fined as the ratio of the 6-8

day variance to the 2-13 day

variance.

• R2 is generally low (Table 3)

→ Weak coupling strength be-

tween weekly PM10 and

GPH850

• Generation of the weekend

effect is largely grounded on

boundary-layer aerosol pro-

cesses.

• FFT analysis using the geopotential height at 850hPa does not explic-itly show a weekly periodicity (Fig. 7).

• Introduction to previous study by Choi et al. (2008)

① They used Fast Fourier Transform to extract periodicity of data, which is also adopted in this study.

② They confirmed the previous findings on the interaction between aerosols and the meteorological conditions in the boundary layers and suggested a possible relationship between cloud formation and aerosols at weekly timescale.

Adapted from Choi et al. 2008

Fig. 1.

ㅡ : normal, ㅡ ; normal + noise

Fig. 2

Fig. 3

Fig 4

Fig 5

• Summer season generally has a strong weekly periodicity, espe-cially in 2002 (Figs. 4-5).

Fig 6

Fig 7

Both cities have strong weekly periodicity in JJA, 2002 (a peak of spectrum nearby 0.14 (7-1day)).

Table 3

• Scientific questions to Choi et al. (2008): Can the semi-weekly weather system also contribute to the weekly variation of aerosols?

• Human activities more likely influence the weekend effects in Beijing and Tianjin.

Strong Weekly Periodic-ity !