Correlation and Time Series Analysis of Tropospheric Hydroxyl Radicals and Solar Ultraviolet Radiation Zhijun Zhao EAS4803 Class Project April, 2008

Background Hydroxyl radical (OH): Atmospheric detergent Extremely reactive Lifetime <1s Concentration < 1 x 10 7 molecule cm -3 (0.4pptv) Major Source: O 3 + hν → O( 1 D) + O 2 ( λ < 330 nm) O( 1 D) + H 2 O → 2 OH Major Sinks: OH + CO + O 2 → CO 2 + HO 2 OH + hydrocarbons, etc → HO 2 + … OH + NO 2 + M → HNO 3 + M

Objective Use measured long term OH and J(O1D) data to verify the dependence of [OH] and solar ultraviolet radiation Use measured long term OH and J(O1D) data to verify the dependence of [OH] and solar ultraviolet radiation Employ time series analysis to illustrate the periodicity of [OH] and solar ultraviolet radiation Employ time series analysis to illustrate the periodicity of [OH] and solar ultraviolet radiation Use cross spectral analysis to show their correlation in the frequency domain. Use cross spectral analysis to show their correlation in the frequency domain.

Data source Meteorological Observatory Hohenpeissenberg (MOHp) in Germany Data converted to 1 hour average. In this project, data have been sorted into monthly averages in some of the experiment to show the long term behavior Acknowledge to Prof. Harald Berresheim in National University of Ireland Galway and Prof. Franz Rohrer in Forschungszentrum Juelich (FZJ), Institut ICG-2: Troposphare Rohrer and Berresheim, Nature, 442, 13, , 2006

Data 1 hour data monthly data

Regression and Correlation Analysis 1 hour data monthly data

Time Series Analysis For the whole 1h data, use Least-square Spectral Analysis (LSSA) by Lomb-Scargle method because data are not evenly distributed J(O 1 D) PSD[OH] PSD Major frequencies: ~1 (1 day) ~ (360 day) Select a small portion of data, interpolate to get evenly distributed data, use periodogram, obtain major long frequency

Time Series Analysis For monthly average data Major period: 12 month

Cross Spectral Analysis Cross-spectral analysis via Welch method Coherence

Conclusion Regression and time series analysis were used to study the [OH] and J(O 1 D). Regression and time series analysis were used to study the [OH] and J(O 1 D). Strong correlation between [OH] and J(O 1 D) was found with little annual variation. Strong correlation between [OH] and J(O 1 D) was found with little annual variation. The daily and annual variation of both [OH] and J(O 1 D) was demonstrated by periodogram, which are highly correlated shown by cross spectral analysis The daily and annual variation of both [OH] and J(O 1 D) was demonstrated by periodogram, which are highly correlated shown by cross spectral analysis