Tougher action is needed to tackle the public health "emergency" of air pollution in Scotland, MSPs have heard.

Holyrood's Environment Committee was told that air quality was not improving fast enough and needed urgent attention.

The Scottish Government's 2015 Cleaner Air for Scotland strategy was also criticised as being "very weak" on measures to combat transport pollution.

Environmental lawyer Anna Heslop, from Client Earth, told the committee: "Whilst the situation is improving, the problem is that it's a public health emergency and the situation is not improving fast enough."

She said that the strategy had fed into the UK Government's air quality plans, due to be published within the next week after UK ministers decided not to appeal against the High Court's rejection of a bid to delay them until after the election.

The UK Government was initially given until April 24 to set out draft measures on reducing illegal levels of nitrogen dioxide pollution after a court ruling last year that existing plans to meet EU-mandated air quality limits were inadequate and must be improved.

"My understanding is that the Cleaner Air for Scotland strategy is not currently under review," Ms Heslop said.

She added: "It would be very disappointing if Scotland's ambition is not increased."

Emilia Hanna, air pollution campaigner at Friends of the Earth Scotland, said Scotland was "a long way behind where we need to be" in addressing air pollution, with four areas of the country in breach of limits for nitrogen dioxide under European law.

"This is a significant health crisis and one that we need to tackle much more quickly," she said.

"We need much tougher action specifically on transport and I think we can point the finger quite firmly at transport, traffic and use of the private car."

She added: "Progress has been quite slow through Cleaner Air for Scotland. Another weakness again is that it doesn't quantify what the impact of the 83 policy measures that it proposes to introduce would be, so there's no way of knowing: does this add up to delivery of the legal limits by 2020?"

Tom Rye, professor of transport and director of the transport research institute at Napier University, told MSPs the strategy was "very weak" on tackling transport pollution particularly in relation to HGVs and trunk roads, where he said it "isn't planning to do enough fast enough".

However, Vincent McInally, environmental health officer at Glasgow City Council, said that while air quality "is presenting a very real risk to public health", Glasgow was "the cleanest it has been since the industrial revolution" with more than 97% of the city meeting all air quality targets.

Will Garrett, spatial policy manager at Edinburgh Council, agreed that while it was "by no means complacent" the picture was improving.