A pilot study but, nevertheless, rare data on the link between CH and smoking.
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J Headache Pain. 2013 Jun 6;14(1):48. [Epub ahead of print]
Impact of continuing or quitting smoking on episodic cluster headache: a pilot survey.
Ferrari A, Zappaterra M, Righi F, Ciccarese M, Tiraferri I, Pini LA, Guerzoni S, Cainazzo MM.
Abstract
BACKGROUND: The majority of patients suffering from cluster headache (CH) are smokers and it has been suggested that smoking may trigger the development of CH. The aim of this pilot survey was to describe: 1. the differences between current, former, and never smokers CH patients; 2. if smoking changed during an active cluster period; 3. if CH changed after quitting.

METHODS: All outpatients with episodic CH according to the criteria of ICHD-II who were consecutively seen for the first time from October 2010 to April 2012 at a headache centre were interviewed by phone using a specifically prepared questionnaire. Statistical differences between continuous variables were analysed by the Student's t-test or the one-way analysis of variance (ANOVA), followed by Newman-Keuls post-hoc testing. Comparisons between percentages were made using the Chi-square test or Fisher's exact test. All data were expressed as the mean +/- standard deviation (SD).

RESULTS: Among a total of 200 patients surveyed (172 males, 28 females; mean age +/- SD: 48.41 +/- 12 years) there were 60%, 21%, and 19% of current, former, and never smokers, respectively. Current smokers reported longer active periods (12.38 +/- 10 weeks) and a higher maximum number of attacks per day (3.38 +/- 1) compared to never smoker CH patients (5.68 +/- 4 weeks, P <0.05 and 2.47 +/- 1, P <0.05, respectively). During the active period most of the patients stated to decrease (45.7%) or not to change (45.7%) the number of cigarettes smoked. Among those who decreased smoking, most (83.8%) reported that they had less desire to smoke. After quitting, the majority of former smokers stated that their headache had not changed.

CONCLUSIONS: PATIENTS WITH EPISODIC CH WHO ARE ALSO SMOKERS APPEAR TO HAVE A MORE SEVERE FORM OF THE DISORDER. HOWEVER, IT IS UNLIKELY THAT BETWEEN CH AND SMOKING THERE IS A CAUSAL RELATIONSHIP, AS CH PATIENTS RARELY IMPROVE QUITTING SMOKING.

PMID:23742010[PubMed]

I think money could be better spent, than going back on
reasearch thats been done and dusted many times.

Yes, most research concludes that in most CH sufferers
smoking has not been found to be a trigger, but will intensify
the pain when having a CH attack

O2 being effective for aborting attacks does not necessarily mean that O2 deficiency is the cause. It makes sense that O2 breaks the NO as some researches suggests.

I think it's also more probable that smoking intensifies attacks because of it's irritating effect over the nose or throat. 

Oddly enough, for me smoking is a definite trigger while I have shadows. But in a later stage of the attack itself, when the pain is slowly decreasing, smoking actually helps.