On bad days in India's congested capital, the air is so murky it slows traffic to a crawl. Conversations are punctuated with rasping coughs. Weak bands of sunlight filter through a grainy sky.
Air monitoring sensors around the landlocked Indian capital have routinely registered levels of small airborne particles at ''hazardous'' levels in recent months - three to four times New Delhi's own sanctioned limit, rivaling Beijing.
While it's uncertain which city has worse smog - there are various toxins to measure and methods differ, among other things - one thing is clear: China's capital is taking steps to improve air quality but New Delhi hasn't done much in recent years to tackle the problem, largely because there's been little public outcry.
Doctors overwhelmingly agree that more people in New Delhi are getting sick from the air pollution, although there is scant data to show it. Air pollution is proven to exacerbate chronic lung ailments, and there is mounting evidence it also leads to stress, coronary diseases and inflammation.
''It seems incredible that the politicians and judges living in Delhi would not be worried about how their families and children are suffering from the bad air,'' said Dr. K. Srinath Reddy, head of the Public Health Foundation of India. ''People have to recognize the extent of the damage happening. That's where the outrage will come in. That's when the action will happen.''
This week, Reddy co-chaired the first meeting of a new Health Ministry committee, formed two months ago with academics, officials and health workers, tasked with recommending ways to protect the public from dirty air.
Their report is due in a year.
Comparing pollution levels between the two megacities, home to a combined 29 million people, seems natural given their iconic status representing Asia's opportunity and growth. They both have gone through breakneck economic development that has transformed their landscapes within a generation, raising living standards but also spewing out loads of pollution.
Decades of policies that favored economic decisions over environmental concerns have taken their toll. Cars now represent the middle-class dream for thousands digging out of poverty, and decades of booming construction has kicked up countless clouds of dust.
There are various ways to measure pollution, but comparisons have generally focused on the microscopic particulate matter, sometimes called black carbon or soot, which can lodge in a person's lungs and fester over time.
In New Delhi, levels of PM 10 - particulate matter that is 10 micrometers in size - have routinely bounced around 400 micrograms per cubic meter the past several months. That's four times the city's legal limit of 100, and well above the World Health Organization's recommended limit of 20. In 2011, the average level rose to about 280.
In Beijing, average annual PM 10 levels have declined to just above 100 last year, according to the Center for Science and Environment, a Delhi-based research and advocacy group that crunched the official numbers.
The Chinese capital is way ahead of its Indian counterpart in terms of in informing citizens about the dangers of pollution. Beijing has launched a health alert system that advises caution on smoggy days, and the term PM 2.5 - particles even smaller than PM 10 and considered more dangerous to health - has become a common part of the vocabulary among citizens, with many checking smartphone apps for the hourly readings.
During high alert times, schools may be closed, industries shut down and government vehicles taken off the roads.
New Delhi has no such alert system or emergency protocols. While the city recently began offering smog data online, power cuts can cause gaps in real-time reporting. And experts say many among the migrant-heavy population are unlikely to see or understand the information.
''It is the state's responsibility to inform people about pollution dangers,'' said Anumita Roychowdhury, research director at the Center for Science and Environment. ''People need to know what they're breathing, even if only so they can demand better.''
Beijing has also launched aggressive control measures, from limiting the number of cars that ply its roads to sanctioning punishments against factories that fail environmental standards.
New Delhi, however, has seen little action since enacting a set of reforms over a decade ago, which included moving industry beyond city limits, building a subway and switching public transportation to cleaner-burning fuel.
Indian authorities are touchy about comparisons between the two cities, and point to seasonal factors, such as when winds die down in the winter and let pollution pool over the capital. But Beijing experiences a rise in pollution once people start burning coal for heat while Delhi's homeless turn to burning wood and piles of trash.
''It is scientifically wrong to compare Delhi and Beijing. The way of measuring (pollution) is different. The cities' weather dynamics are different,'' said M.P. George, who heads air monitoring with six citywide sensors for the Delhi Pollution Control Committee in addition to five managed by federal authorities.
Regardless of which city is worse, experts warn that pollution is a serious health hazard. Globally, pollution-related diseases kill 3.2 million people each year, with two-third in developing Asia, according to the 2012 multi-institutional report titled the Global Burden of Disease.
In New Delhi and other major Indian cities, ''we are seeing more patients than we saw before, especially children'' with recurring nose, throat and chest infections, said Dr. Sundeep Salvi of the Chest Research Foundation in the southern city of Pune. Such infections can inhibit lung growth - another problem area for India.
A study published in the Lancet medical journal in October showed the lung capacity of nonsmoking Indian adults is just two-thirds that of North America and Europe. The study did not analyze various factors, from pollution to nutrition, that might account for the difference, but doctors unaffiliated with the study said they believed air pollution was likely a major cause.
''If pollution continues to get worse, today's children may have even less lung capacity,'' Salvi said.