Ultraviolet Intensity In Zhengzhou And Its Medical Implication

Background and objectivesUV (ultraviolet, UV) radiating to the earth’s surface from sunlight can be divided into UVA (ultraviolet A, UVA) and UVB (ultraviolet B, UVB) according to their wavelengths. UV may inhibit or even kill the bacterias on skin surface, and is essential in synthesis of vitamin D. Addtionally, U V may also lead to and exacerbate various photosensitive diseases.UVA radiation may induce photoaging,pigmentation, cancerization, and immune suppression; whereas UVB radiation may be associated with sunburn, protein expression disordering, and cancerization. The purpose of this study is to measure and analyse UVA and UVB intensity statistically throughout one year in Zhengzhou, in order to provide a more detailed scientific basis for the inhabitants of that city in utilizing sunlight and sun protection.MethodsUVA and UVB intensities were measured at8:00、10:00、12:00、14:00and16:00on every Tuesday, Thursday and Saturday from December1,2011to November29,2012. The rainy, snowy, and windy (grade6and greater) days were excluded. Repeated measures analysis of variance was utilized to compare the respective statistical differences of UVA intensities and UVB intensities in the four seasons, and at the five time points. Multiple pairwise comparisons (Bonferroni test) was applied to pairwisely compare the respective statistical differences of UVA intensities and UVB intensities in the four seasons, and at the five time points.Results1. The mean intensities of ultraviolet A in spring, summer, autumn, and winter were1542.06±94.27μw/cm2,1828±92.95μw/cm2,1017.98±97.09μw/cm2, and534.94±94.27μw/cm2, respectively; and the intensities of ultraviolet B were109.04±7.12μw/cm2,136.32±7.02μw/cm2,76.91±7.33μw/cm2,and34.56±7.12μw/cm2, respectively. Although there was no statistical difference in ultraviolet A intensity in spring versus in summer (Pspring vs summer=0.195), the differences in any rest two seasons were all significant (P spring vs autumn=0.001,Pautumn vs winter=0.003, and all the rest Ps<0.001). There were no statistical differences in ultraviolet B intensity both in spring versus in summer (Pspring vs summer=0.043), and in spring versus in autumn vs autumn=0.012); whereas differences presented in any rest two seasons (All Ps<0.001)2. The yearly mean intensities of ultraviolet A at8:00,10:00,12:00,14:00and16:00were590.29±38.28μw/cm2,1332.02±53.91μw/cm2,1894.82±75.88μw/cm2,1584.04±67.73μw/cm2, and752.80±36.85μw/cm2, respectively; and those of ultraviolet B were41.18±2.95μw/cm2,100.10±3.96μw/cm2,142.76±5.67μw/cm2,111.64±5.04μw/cm2, and50.36±2.67μw/cm2, respectively. Among the five measured time points, the ultraviolet A intensities at any two time points were statistically different (all Ps<0.001). And the differences of the ultraviolet B intensities at any rest two measured time points were also significant (P10.00vs14:00=0.014, and all the rest P.s<0.001), except the ultraviolet B intensities at8:00versus at16:00(P8.00vs16:00=0.030).ConclusionsThe Ultraviolet intensities in Zhengzhou in the four seasons of a year and at different measured time points of daytime may be different. However, in any seasons, sun protection measures should be taken according to ultraviolet intensity at the time, ultraviolet category one is sensitive and his/her minimal erythema dose to that category of ultraviolet.