Smog analysis and its effect on reported ocular surface diseases: A case study of 2016 smog event of Lahore

A comparative cross sectional study was conducted in order to analyze the pollutants (CO, NOx, SO2, O-3, VOC and PM) present in the event of Lahore smog that was observed on 2-5 Nov 2016 in relation to the baseline condition of the ambient air measured during the same period in the previous year i.e. 2015. The effect of smog was determined based on ocular surface diseases reported by patients, using data' taken from tertiary care hospitals during the 2-3 November 2016 Lahore smog. The data was compared with that from the previous year (2-3 November 2015) being considered as baseline. For analysis of the smog and its comparison with baseline conditions, three sites were selected within Lahore city i.e. Mall Road, Gulberg and Township. The AQI for these sites were determined with the analysis of ambient air that was done through USEPA approved reference methods. The data on the number of patients having ocular surface diseases due to smog were collected from tertiary care hospitals i.e. Shiekh Zaid and Mayo Hospitals which were randomly selected. The clinical method used has been implicitly elaborated and it has been explained very clearly how all the clinical diagnoses were executed. The highest concentration of pollutant analyzed during smog was that of NOx which was almost 17 times higher than the baseline value. The other pollutants SO2 and O-3 were four times, CO, VOC and PM2.5 two times and PM10 was six times higher than the baseline value. Although the values of SO2 and PM2.5 were greater than the baseline values they did not exceed the Pakistan Environmental Quality Standards (PEQS) limits. The Air Quality Index- AQI was found to be six times higher than the baseline which represents a very poor air quality during smog days. The metrological conditions during the smog event were cool temperatures, calm winds and high humidity that ultimately triggered the photochemical reaction which caused the smog. The data taken from hospitals revealed that out of 700 patients 200 were reported in 2015 and 500 were reported in 2016 with diseases including dry eyes (12%) and (13%), irritation (20%) and (21%), lid erosion (4%) and (5%), corneal diseases (7%) and (8%),uveitis (3%) and (4%) and lacrimation (11%) and (7%) respectively. The study ultimately revealed that there was a 60% increase in the number of patients reported with ocular surface diseases (dry eyes, irritation, lid erosion, comeal diseases, conjunctival diseases, uveitis, and lacrimation) during periods of smog as compared to baseline conditions.