Semi-quantitative monthly mean surface ozone observations from station Guarda

The dataset consists of a set of semi-quantitative surface ozone observations (hereinafter O3), together with relative humidity observations at the same temporal scales. The dataset consists of monthly mean observations from 23 observatories, listed on Table 1. The datasets are from the period 1872 to 1888 at 22 of the observatories. They're extensions in times range between 17 and 3 years for monthly mean observations. The other dataset from the Observatory Infante D. Luiz, the longest semi-quantitative surface ozone observations data series known to date, spans 58 years for monthly data (1855 to 1913). For more details see Tables 2a and 2b in Añel et al., 2024. The O3 observations were recovered and manually digitalized from the Annaes do Observatory Infante D. Luiz published between 1863 and 1915 (Fradesso da Silveira, 1863; De Almeida, 1915). The O3 observations were part of the regular meteorological observations conducted at Portugal and former colonies network of meteorological observatories and outstations controlled by the Infante D. Luis Meteorological Observatory (Lisbon), created in 1857 (Raposo, 2017). Geographically the dataset consists of O3 observations at the 23 observatories listed on Table 1, between 42°N and 9°S in latitude and 27°W and 15°E. Eighteen observatories are located at the Iberian Peninsula and five in Africa. Three of those observatories are insular, two at the Azores islands and one at Madeira Island. The O3 observations were conducted using Schönbein test-paper method, also called "ozonoscope". It was based on the color-change of an indicator strip of blotting paper coated with starched potassium iodide. The paper strip was exposed to air between 8 and 24 hours protected from solar radiation and rain. The method applied in the Portuguese observatories was the one from Berigny (1958) who defined the operating procedure, introducing a more precise chromatic scale graduated from 0 to 21 and selected he best quality of impregnated paper. That on was the Berzelius paper manufactured by James a chemist at Sédan (Marenco et al, 1994) that is often referred in logbooks containing measurements as the cale of "James de Sédan". (Añel et al., 2024).

该数据集包含一组半定量地表臭氧观测数据（以下简称O3），以及相同时间尺度下的相对湿度观测数据。数据集包含来自23个观测站的月均观测值，这些观测站列于表1中。其中22个观测站的数据集覆盖1872年至1888年；对于月均观测值，其时间范围的延长跨度为3至17年不等。另一组来自Infante D. Luiz观测站的数据集，是目前已知最长的半定量地表臭氧观测序列，其月数据跨度达58年（1855年至1913年）。更多细节请参见Añel等人2024年发表的表2a和表2b。

O3观测数据是从1863年至1915年出版的《Infante D. Luiz观测站年鉴》（Annaes do Observatory Infante D. Luiz）中复原并手动数字化得到的（Fradesso da Silveira，1863；De Almeida，1915）。这些O3观测数据是葡萄牙及前殖民地气象观测站与分站网络常规气象观测的一部分，该网络由1857年成立的里斯本Infante D. Luiz气象观测站管理（Raposo，2017）。

从地理分布看，数据集包含表1所列23个观测站的O3观测数据，这些站点位于北纬42°至南纬9°、西经27°至东经15°之间。其中18个观测站位于伊比利亚半岛，5个位于非洲；3个为岛屿观测站，2个在亚速尔群岛，1个在马德拉岛。

O3观测采用舍恩拜因试纸法（Schönbein test-paper method），又称臭氧测定仪法（ozonoscope）。该方法基于涂有淀粉碘化钾的吸水指示试纸的颜色变化：试纸条在避光避雨条件下暴露于空气中8至24小时。葡萄牙观测站采用的是Berigny（1958）提出的方法，该方法明确了操作流程，引入了精度更高的0至21级色阶，并选用了最优质量的浸渍试纸。所用试纸为Sedan的化学家James生产的Berzelius试纸（Marenco等人，1994），在包含测量数据的日志中常被称为“James de Sedan色阶”（Añel等人，2024）。