Investigation on spatiotemporal distribution of aerosol optical properties over two oceanic regions surrounding Indian subcontinent during summer monsoon season.

Columnar spectral aerosol optical depths (AODs) and total suspended particulate matter (TSPM) concentrations were collected on board the Oceanographic Research Vessel (ORV) of Sagar Kanya (SK) during 7-21 June 2014 (SK-313) and 31 July-14 August 2015 (SK-323) over the Arabian Sea (AS) and Bay of Bengal (BoB), respectively, for the two successive years during summer monsoon season. AOD measured at 500 nm (AOD500) varied significantly from 0.08 to 0.66 (0.07 to 0.60), with a mean of 0.48 ± 0.13 (0.34 ± 0.13) over the BoB (AS) during SK-313 (SK-323). It simply implies that aerosol load was higher over BoB, not variability as the standard deviations of AOD over both oceans are identical (0.13). Daily AOD500 ranged between 0.15 and 0.60 accounted for 70-75% of the total occurrences over two oceanic regions. Mean Ångström exponent (α or alpha) and Ångström turbidity coefficient (ß or beta) were found to be 0.43 ± 0.17 (0.39 ± 0.19) and 0.37 ± 0.15 (0.27 ± 0.13), respectively, which are higher over the AS during SK-323 (SK-313) that indicate predominance of coarse-relative to fine-mode particles. On the other hand, the spectral curvature and second derivative of alpha (α') also showed significant contribution of coarse-mode particles over fine during the two campaigns. Further, column aerosol size distribution (CSD) derived from the King's inversion also exhibited bimodal distribution with a predominant peak observed in the coarse mode (~1.0 µm) compared to the fine mode at a geometric mean radius at ~0.1 µm over two oceans. The observed data showed that the two marine regions are significantly influenced by various types of aerosols with a predominance of mixed type (MT) of aerosols. From the morphological study, it is inferred that the particles are a flake, spherical, irregular, and in flower and aggregated shapes conducted for the TSPM samples collected during SK-323 over the AS. Finally, the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model is used to study the impact of long-distance transported aerosols and identify their sources.

Loss of crop yields in India due to surface ozone: an estimation based on a network of observations.

Surface ozone is mainly produced by photochemical reactions involving various anthropogenic pollutants, whose emissions are increasing rapidly in India due to fast-growing anthropogenic activities. This study estimates the losses of wheat and rice crop yields using surface ozone observations from a group of 17 sites, for the first time, covering different parts of India. We used the mean ozone for 7 h during the day (M7) and accumulated ozone over a threshold of 40 ppbv (AOT40) metrics for the calculation of crop losses for the northern, eastern, western and southern regions of India. Our estimates show the highest annual loss of wheat (about 9 million ton) in the northern India, one of the most polluted regions in India, and that of rice (about 2.6 million ton) in the eastern region. The total all India annual loss of 4.0-14.2 million ton (4.2-15.0%) for wheat and 0.3-6.7 million ton (0.3-6.3%) for rice are estimated. The results show lower crop loss for rice than that of wheat mainly due to lower surface ozone levels during the cropping season after the Indian summer monsoon. These estimates based on a network of observation sites show lower losses than earlier estimates based on limited observations and much lower losses compared to global model estimates. However, these losses are slightly higher compared to a regional model estimate. Further, the results show large differences in the loss rates of both the two crops using the M7 and AOT40 metrics. This study also confirms that AOT40 cannot be fit with a linear relation over the Indian region and suggests for the need of new metrics that are based on factors suitable for this region.