Temporal and spatial shifts in the chemical composition of urban coastal rainwaters of Kuwait: The role of air mass trajectory and meteorological variables

The rainwater chemistry encompasses the signatures of geogenic and anthropogenic processes along the regional air mass movement apart from the local sources. The predominance of dust events and anthropogenic emissions in arid regions facilitate new particle formation. Further, rain events of different seasons depict moisture sources from diverse regions reflecting variation in the regional geochemistry with respect to seasons. Hence, to characterize the geochemical composition of rainwater, the study has focused on an integrated approach by considering regional transport, meteorological components and possible local sources. A total of 74 rainwater samples were collected from 27 rain events in 2018, 2019, and 2022, representing urban coastal areas of Kuwait predominantly of Ca-SO4-HCO3 type. The average pH and electrical conductivity of the rainwater were 7.18 and 140 μS/cm, respectively. The sea salt fractions calculated relative to Kuwait seawater ranged from 25.6 to >100 %, with higher values attributed to anthropogenic sources. Sea salt fraction, ion ratios, principal component analysis and factor scores revealed the terrestrial and anthropogenic sources apart from marine contributions. In addition, new particle formation and aerosols contributed to the rainwater chemistry involving SOx, NOx, and photochemical reactions during higher relative humidity and lesser wind speed. The HYSPLIT reflected that the moisture sources were largely from western regions of the study area, and those of December and January events had long-distance travel across the Azores high originating from northeast America. The trajectories of the November events are observed to originate from the Caspian/Black Sea region in the northeastern part of Kuwait with a relatively shorter distance of travel. The rainfall samples had higher ionic concentrations, and saturated with aragonite and calcite minerals in a few locations specifically after the dust events, while the subsequent rain events were less polluted.

Impact of crop residue burning in Haryana on the air quality of Delhi, India

Crop residue burning (CRB) over northern India is a major air quality and human health issue. The present study assesses the impact of PM10, PM2.5, NO2 and SO2, emitted during CRB activities in Haryana on the air quality of Delhi. The transition from pre-burning to burning period, in both rabi and kharif seasons, shows considerable increase in pollutant concentrations. PM10 and PM2.5 concentrations exceeded NAAQS limits by 2-3 times, while NO2 and SO2 stayed within the limits. MODIS fire observations used to estimate CRB fire counts (confidence ≥80%) shows that rabi (burning period) fires in Haryana are ~3 times higher and more intense than in kharif. Furthermore, backward trajectories shows air mass movement from Haryana, Punjab and Pakistan. Thus, pollutants emitted reach Delhi via air masses, deteriorating its air quality. Meteorological conditions influence pollutant concentrations during both seasons. Frequent dust storms in rabi, and Dusshera and Diwali firework celebrations in kharif season exacerbate air pollution. In rabi, PM10 and PM2.5 have a significant negative association with (relative humidity) RH and positive association with (air temperature) AT. High AT during pre-monsoon, accompanied by low RH, loosens up soil particles and they can easily disperse. Stronger winds in rabi season promote NO2 and SO2 dispersion. In kharif, lower AT, higher RH and slower winds exist. Both PM10 and PM2.5 have a negative association with AT and (wind speed) WS. With lower temperature and slower winds during winter, pollutants are trapped within the boundary layer and are unable to disperse. As expected, NO2 has a significant negative association with AT in Haryana. However, in case of Delhi, the association is significant but positive, and could be due to the odd-even scheme imposed by the Delhi government. More research is needed to determine the health effects of Haryana's rabi CRB activities on Delhi.